Triband opinions
RICK DYKSTRA
My tower came down recently in high winds along with my TH6 tribander.
I'm trying to decide what to put back up. Does anyone know how the
various antennas from Hygain, KLM, Cushcraft ect. compare? I'd like
to stay around the same size... 24' boom.
Thanks,
Rick KD8CP
Lew McCoy
Rick: I have reviewed most of the trap beams during my career and I
have found that the Sommer beam is the best by quite a bit, Hy Gain is
extremely honest in their gain claims as compared to other
manufacturers. I can tell you this and you can take it to the
bank--none of the trap beams, regardless on the numbr of element, will
exceed 6.2 to 6.5 dbd--that was proven years ago in range measurements
and the science has not changed.
Lew McCoy, W1ICP
Lew McCoy
and Rick pointed out that I gave the impression the Sommer beam was a
trap affair. I am sorry I gave that impression--the Sommer beam uses
log periodic typre of feed to all elelements--there are no traps
involved. I am rather high on the antenna as I have had one up for over
ten years--taking it down on occasion to test another beam etc but
always puttiong back up the Sommer--you can make you own con clusion
from that.
73 Lew Mccoy< W1ICP
Lew McCoy
Lew McCoy wrote:
>
> RICK DYKSTRA wrote:
> >
> > My tower came down recently in high winds along with my TH6 tribander.
> > I'm trying to decide what to put back up. Does anyone know how the
> > various antennas from Hygain, KLM, Cushcraft ect. compare? I'd like
> > to stay around the same size... 24' boom.
> >
> > Thanks,
> > Rick KD8C
> Rick: I have reviewed most of the trap beams during my career and I
> have found that the Sommer beam is the best by quite a bit, Hy Gain is
> extremely honest in their gain claims as compared to other
> manufacturers. I can tell you this and you can take it to the
> bank--none of the trap beams, regardless on the numbr of element, will
> exceed 6.2 to 6.5 dbd--that was proven years ago in range measurements
> and the science has not changed.
>
trap antenna--I am sorry if I misled anyone. The Sommer beam concept
was actually derived (invented) by a German who lived in Australia and
he wrote an article about the beam which appeared in Ham Radio, many
years back. Alf Sommer came along and improved on the beam I
eventually got one and tested it. I have had mine up for at least ten
years--I keep testing various beams but I find that none of them compare
to the Sommer so that is what I keep up. The antenna uses nearly all
elements driven--I believe that anyone interested can get a description
circular from Sommer beams. It has no traps or lossy elements. It
continues to be the best multiband performer I have seen ( maybe I
should get payed by Sommer--hi!) but the darn thing is a very good
antenna. I have to tell anyone reading my posts--I have been around
loner than most hams--I am 81--still writing--but the beauty of getting
that old is I don't have to stand still for the crap that advertisers
like to put out to us. Or for that matter some writers, So, if you
don't like to hear that your particular antenna is a dog--forgive me.
What I like--the G5RV--it is a good sound technical design--cheap to
build and will work like a charm.
Any centerfed dipole using tuned feeders a la ladder line or open wire
line. Coax may be OK for single band operation.
Verticals--what can I say--I have been credited with the old saying
vertical readiate equally poorly in all directions. Under rare
circumstances a vertical can do a good job but generally speaking, a
vertical will be popular b ecause hams see that low angle that is
suppose to come off the antenna--it does't take up much real estate--but
on a scale of 1 to 10--Im would give it a three--better than a rain
gutter--probably better than a random wire but that gets it up to a
three. A G5RV is cheaper--much much better performer, etc.
Beams--avoid trap beams.....Those are periods.
Let's look at gain--a trap beam no matter whose--has a maximum gain for
6.2 dbd gain--this has been proven many time on qualified range
measurements. adding more elements does not add more gain--not like a
straight Yagi.
Compare trap Yagis to quads--a quad has just about 6 dbd gain--no trap
losses and very little weather problems except for icing. The Yagis
cost from $500 on up to well over $1000. Thatb is a fact. A quad, five
band, will cost just about $300 and all the manufacturers that make them
are reputable.
These are all considerations one must make when deciding on antenna--one
can argue small point of difference with these statements and I know
they will but be assured--if they are going to be honest, they will
agree.
All of you hang in there--I am off to Dayton in a few days--maybe see
you there.
Lew Mccoy, W1ICP
iation
Jari Jokiniemi
In article <337230...@zianet.com> Lew McCoy <mc...@zianet.com> writes:
Let's look at gain--a trap beam no matter whose--has a maximum gain for
6.2 dbd gain--this has been proven many time on qualified range
measurements. adding more elements does not add more gain--not like a
straight Yagi.
Just out of curiosity, how many elements did that best trap yagi
giving 6.2 dBd have and what was the band the measurements were made
on?
--
Jari Jokiniemi, jari.jo...@tekla.fi, OH2MPO, OH3BU
Tekla Oy, Koronakatu 1, 02210 Espoo, +358-9-8879 474
Lew McCoy
William E. Sabin wrote:
>
> Tom Rauch wrote:
> >
> > When I run 1500 watts to a trap antenna, why don't the traps melt if
> > the loss is so high?
>
> This is a common misconception, Tom. Actually, traps are melting all
> the time, but they do it late at night, and self-heal by sunup.
>
> Bill W0IYH
Bill: I don't think Tom has been around long enough to really have
traps self destruct from heat--even though they do quite
frequently--except he wants case and poimnt and I haven't kept those
kind of records/
.
Lew, W1ICP
Lew McCoy
and the KT34 series. Several three element trap yagis were tested
including Moseley, Cushcraft, Hy Gain. The three element beams c ame in
at just about 6.1 dbd--Hy Gain beams of four, five an dthe TH6 came in
at 6.2 dbd. The KT34 checked out like wise. The KT34XA was lightly
better but not that much. (It made me believe at the time--and I still
do--that the effective aperture of such an antenna suffers with lineat
loading--in other words--it is really a smaller antenna. This is why I
have never been too high on shortened 40 or 80 meter beams. Don't
misundertand, they work but not as well as the manufacturer likes to
cliam. A Cushcraft four element trap was also the same. I still don't
want to divulge the range were these were done but I stll have all the
charts, graphs, front to back.
Etc. I was employed by ARRL in their technical department at the time.
As you can well assume, this was and still is a very touchy subject as
regards antenna manufacturers.
Lew McC oy, W1ICP
Lew McCoy
Jari Jokiniemi wrote:
>
> In article <33730b2...@news.frazmtn.com> w6...@frazmtn.com (Jesse Touhey) writes:
> Hi Jari, in my opinion, 6.2dbd is very optimistic to achieve on every
> band of a 3 element, tri-band trap Yagi..... 5dbd is more realistic.
>
> I agree. That's why I asked how many elements the antenna had and on
> what band was the measurements made on. I am not quite sure if he was
> talking about 3 elements only. Quite the contrary, I got the
> impression that on those measurements 6.2 dBd was the best gain
> measured on any trap beam. Even if it had 11 elements. But on what
> band? I would suspect that a 6 element 3 band trap yagi should perform
> quite well on 28 MHz. It is practically a monobander. The same beam
> might at the same time be quite bad on 14 MHz.> Tekla Oy, Koronakatu 1, 02210 Espoo, +358-9-8879 474Jari and Jesse: You guys are right on. The antennas tested were
tweaked for maximum gain. The 6. 1 to 6.2--I just examined all the
charts I have--were for 20 meters. Some of the tests were made on the
antennas as they came out of the box and some only hit 5 dbd. None of
were surprised. On antenna, I really should not name but if I get
pushed enough I might--was checks at minus 2 dbd on 20 meters. Like I
say--I still have all the charts and graphs and would be happy to answer
any questions--if I can.
It is no secret but I remember quite clearly about 30 years ago I went
out to St. Louis to visit Moseley. I asked if I coud see their antenna
range. They took me up on the roof and across a sea of power lines,
etc. they said the receiving location "was out there." Nuff said???
Lew McCoy, W1ICP
Lew McCoy, W1ICP
Lew McCoy
Tom Rauch wrote:
>
> On Thu, 08 May 1997 08:44:05 -0600, Lew McCoy <mc...@zianet.com>
> wrote:
> .222222
> >Rick: I have reviewed most of the trap beams during my career and I
> >have found that the Sommer beam is the best by quite a bit, Hy Gain is
> >extremely honest in their gain claims as compared to other
> >manufacturers. I can tell you this and you can take it to the
> >bank--none of the trap beams, regardless on the numbr of element, will
> >exceed 6.2 to 6.5 dbd--that was proven years ago in range measurements
> >and the science has not changed.
>
> Interesting number, but I wonder how that could possibly be true.
>
> If an additional properly tuned element is added and the gain remains
> the same because the loss in the element is so high, why does the
> FIRST additional parasitic element add gain?
>
> When I run 1500 watts to a trap antenna, why don't the traps melt if
> the loss is so high?
>
Tom: Adding an element to a trap beam does not just add losses, if you
understand the sacrifices in spacing, balancing front to back, etc, in
trap beams you would realize that it is not just losses. We could argue
until hades freezes over but all opf the range measurements that were
made showed that these antennas just did not exceed 6.2 to 6.3 dB gain.
It is a simple technical fact that any three band or five band trap
antenna sacrifices gain in order to obtain a multiband match, in order
to obtain front-to-back and all the other things that go into making a
Yagi (single band) work. This has been pointed out in the literature
and tests for years and anyone who has studied the problem knows. I
just don';t want to get into an argument with you--it becomes entirely
pointless. I give you credit for b eing very smart--in some places--but
you like to be critical of something you haven't tried as wit the
UniHat--I know the results and tests and I know what that antenna does
nut you like to shoot it down based on your knowledge of short verticals
but quite simply--there is a whole world out there that you have never
entered.
Good Luck
And by the way--I know that you don't like range measurements because
they do not usually include different angles--that may be but
nevertheless they prove comparative gains when all antennas are tested
at the same angle.
Lew McCoy.
Jesse Touhey
On 09 May 1997 05:06:54 GMT, j...@tekla.fi (Jari Jokiniemi) wrote:
>
>In article <337230...@zianet.com> Lew McCoy <mc...@zianet.com> writes:
> Let's look at gain--a trap beam no matter whose--has a maximum gain for
> 6.2 dbd gain--this has been proven many time on qualified range
> measurements. adding more elements does not add more gain--not like a
> straight Yagi.
>
>Just out of curiosity, how many elements did that best trap yagi
>giving 6.2 dBd have and what was the band the measurements were made
>on?
>--
>Jari Jokiniemi, jari.jo...@tekla.fi, OH2MPO, OH3BU
>Tekla Oy, Koronakatu 1, 02210 Espoo, +358-9-8879 474
Hi Jari, in my opinion, 6.2dbd is very optimistic to achieve on every
band of a 3 element, tri-band trap Yagi..... 5dbd is more realistic.
I doubt if there is a 3 el, full size, mono bander with spacing and
elements tuned for max gain that will give much over 7dbd. One must
also consider matching loss. Perhaps Lou, will give a name to the
6.2dbd, 3el trapped Yagi, and if he personally conducted the dipole
comparisons on a range with calibrated equipment. Or, is the 6.2dbd
figures from Hygain?
Tom Rauch
William E. Sabin
Tom Rauch wrote:
>
> When I run 1500 watts to a trap antenna, why don't the traps melt if
> the loss is so high?
Jari Jokiniemi
In article <33730b2...@news.frazmtn.com> w6...@frazmtn.com (Jesse Touhey) writes:
Hi Jari, in my opinion, 6.2dbd is very optimistic to achieve on every
band of a 3 element, tri-band trap Yagi..... 5dbd is more realistic.
I agree. That's why I asked how many elements the antenna had and on
what band was the measurements made on. I am not quite sure if he was
talking about 3 elements only. Quite the contrary, I got the
impression that on those measurements 6.2 dBd was the best gain
measured on any trap beam. Even if it had 11 elements. But on what
band? I would suspect that a 6 element 3 band trap yagi should perform
quite well on 28 MHz. It is practically a monobander. The same beam
might at the same time be quite bad on 14 MHz.
--
Jesse Touhey
On Fri, 09 May 1997 12:29:03 GMT, W8J...@worldnet.att.net (Tom Rauch)
wrote:
>On Thu, 08 May 1997 08:44:05 -0600, Lew McCoy <mc...@zianet.com>
>wrote:
>.222222
>>Rick: I have reviewed most of the trap beams during my career and I
>>have found that the Sommer beam is the best by quite a bit, Hy Gain is
>>extremely honest in their gain claims as compared to other
>>manufacturers. I can tell you this and you can take it to the
>>bank--none of the trap beams, regardless on the numbr of element, will
>>exceed 6.2 to 6.5 dbd--that was proven years ago in range measurements
>>and the science has not changed.
>
>Hi Lew,
>Interesting number, but I wonder how that could possibly be true.
>
>If an additional properly tuned element is added and the gain remains
>the same because the loss in the element is so high, why does the
>FIRST additional parasitic element add gain?
>
>When I run 1500 watts to a trap antenna, why don't the traps melt if
>the loss is so high?
>
>73 Tom
Hi Tom, what do you think is ment by "The Sommer beam is the best by
quite a bit"? If you know why I would appreciate a technical
discussion.
73, Jesse, W6KKT
Tom Rauch
On Fri, 09 May 1997 23:49:57 GMT, w6...@frazmtn.com (Jesse Touhey)
wrote:
>Hi Tom, what do you think is ment by "The Sommer beam is the best by
>quite a bit"? If you know why I would appreciate a technical
>discussion.
>73, Jesse, W6KKT
My puzzlement is how accurate this statement is:
>Rick: I have reviewed most of the trap beams during my career and I
>have found that the Sommer beam is the best by quite a bit, Hy Gain is
>extremely honest in their gain claims as compared to other
>manufacturers. I can tell you this and you can take it to the
>bank--none of the trap beams, regardless on the numbr of element, will
>exceed 6.2 to 6.5 dbd--that was proven years ago in range measurements
>and the science has not changed.
The statement sounds quite authoritative, but it certainly requires
some pretty accurate field strength data for support. I wonder how the
data was taken, and which reviews presented the measured FS data.
73 Tom
Tom Rauch
On Fri, 09 May 1997 22:21:43 -0600, Lew McCoy <mc...@zianet.com>
wrote:
>Tom: Adding an element to a trap beam does not just add losses, if you
>understand the sacrifices in spacing, balancing front to back, etc, in
>trap beams you would realize that it is not just losses.
That's common knowlege Lew, but over and over again you blame the
traps. You tout the Sommer antenna because you say it has no "lossy
traps". Now you throw in tuning and spacing. Was the Sommer antenna
tested on the test range?
Which is it? Is the lack of full performance caused by the traps or
the fact the antenna is mis-tuned and mis-spaced?
Once again, your statement:
> manufacturers. I can tell you this and you can take it to the
> bank--none of the trap beams, regardless on the numbr of element, will
> exceed 6.2 to 6.5 dbd--that was proven years ago in range measurements
> and the science has not changed.
You seem to claim....NO matter what, the gain of any trap antenna, no
matter how many elements, can NEVER exceed 6.5 dBd.
As I understand it, the old TH6, the antenna you cite as a multi-
(more than three) element trap antenna example, only has THREE active
elements on 20 meters. On fifteen meters, the TH6 is also a three
element antenna, and on ten meters it is four active elements.
The TH6 employs differing numbers of active traps on different bands.
Some elements are trapped, and some are not trapped.
What does comparing a three element antenna to a three element antenna
prove about additional elements not helping gain????? In order to
prove the gain was limited by the traps, I would think you would have
to have data from a four or more element antenna with TRAPS in the
elements!
From that data alone, your claims make no sense. Your finger is
pointed accusingly at the trap, yet you use an antenna that has three
untrapped parasitic elements as an example to support statements that
"trap antennas are poor performers".
You cite the poor gain of the TH6 as "proof" increasing the number of
elements adds no gain, yet the TH6 is just a three element antenna
(just like the others) on the band you gave data for!
When Iook at the data you just posted, I conclude fewer traps and
better spacing (the TH6) actually might make no great difference at
all!
>pointless. I give you credit for b eing very smart--in some places--but
>*you like to be critical of something you haven't tried as wit the
>UniHat--I know the results and tests and I know what that antenna does
>nut you like to shoot it down based on your knowledge of short verticals
>but quite simply--there is a whole world out there that you have never
>entered.
You mentioned the Unihat.
Let's look at your claims with the Unihat published in December 1994
CQ. In that text, claims were made the Unihat design offered improved
performance because the "folded wires" increased the radiation
resistance and improved efficiency.
Any knowledgeable antenna person knows folding the element in a given
spatial area provides no magical improvement in efficiency or loop
radiation resistance. Fancy folds that increase the impedance seen by
the coax feedline most certainly do not reduce dependence on a good
ground system.
A folded dipole is no more efficient than a single wire dipole with
the same net copper area. In other words, if we cut the folded dipole
in the center and fed it like a conventional dipole, antenna
efficiency, pattern, current distribution, and loss would remain
exactly the same.
When this same feed system is applied to a vertical, readers are
expected to understand and accept claims some form of magic takes
place.
In a Marconi antenna, common mode current (the ONLY current that
causes radiation) flowing in the radiator HAS to be equaled by the
same NET current flowing in the ground connection. Nothing is gained
or changed by changing the feedpoint, except the impedance seen by the
feedline changes.
There is no question the two page long radiation resistance spiel in
the review is totally incorrect.
The only thing that remains is the "comparison". Your article
specifically states your reference antenna was a dipole 180 feet long
and 60 feet high.
Such a reference antenna is laughable on 160 meters. On 160, the
reference antenna is a SHORT dipole. It is also a high angle radiator
placed less than 1/8 wl above lossy ground.
On 80 meters, the reference is longer than full size half wave antenna
but is still less than 1/4 wl above earth. Not what I consider to be a
good low angle radiator.
Only on 40 does the reference dipole antenna start to become what I
consider a "good" antenna. On the other bands it is a high angle
antenna likely having considerable loss.
I can give a specific example of how "good" a low dipole is on 160
Lew. I had a 40 meter extended double zepp here a few years ago. It
was 170 feet long, fed with open wire line, and 130 feet or so high.
On 160 meters, my 130 foot high 170 foot long antenna NEVER beat my
1/4 wl vertical at ANY distance. During nightly ragchews on 1855, the
dipole was consistantly 10 to 15 dB weaker than my vertical in
Mississippi and Alabama....a distance of a few hundred miles. On the
west coast the dipole was SEVERAL S units weaker, night after night.
When Frank, W5NTJ, (in Mississippi) switches from his FULL size dipole
at 100 feet to a 1/4 tower with almost no ground, the tower is
generally about 3 dB or so better here.
You seem to play up experience, so let me say say this. I've worked
160 since 1963. I have nearly 200 countries on 160, and was the first
station east of the Rockies to work JA through the Loran. I've worked
VK,SM, G, DL, and dozens of South Americans from my mobile on 160. I
was the first W8 to work JT1, ZD8, and dozens of other countries on
160. I held morning skeds with VS6DO, and could work Paul on SSB and
CW nearly every day of the week. On nearly any winter morning, I can
work dozens of JA's on 160 from Atlanta.
In all my years of heavy 160 activity, I've NEVER been impressed with
the performance of a full size 60 foot high dipole on 160, let alone a
180 ft long antenna. I can't think of a single big signal on 160
using a low dipole, even a 30 ft high inverted L is better.
I would never use a crummy reference antenna like a 60 ft high 180 ft
long dipole to form conclusions some other antenna is an "outstanding
performer". If I was limited to a double zepp antenna at 60 feet, and
compared it to a lousy vertical antenna, I'd likely be enamored with
even the poorest vertical.
At the very best, it's hard to determine "good" when the reference is
poor and the test so emperical. Certainly the theory was totally
wrong.
>And by the way--I know that you don't like range measurements because
>they do not usually include different angles--that may be but
>nevertheless they prove comparative gains when all antennas are tested
>at the same angle.
The above statement is totally incorrect. Antennas MUST be measured at
the main lobe maxima in any gain comparison. Measuring in a minor
lobe, or at any other single point outside the maximum point of the
main lobe of each antenna, tells us absolutely nothing at all.
As a matter of fact, if we measure just off the peak of the main lobe
(say at the half power point), the LOWER FS producing antenna (overall
antenna style being equal) will have the MOST field strength!!!!!
If you look Lew, you'll see HIGHER directivity antennas have NARROWER
main lobes. Measuring at only one point tells us nothing about the
true gain of an antenna, or how it compares to another antenna, UNLESS
we measure at the main lobe peak of each antenna.
73, Tom
Gary Coffman
On Fri, 09 May 1997 12:29:03 GMT, W8J...@worldnet.att.net (Tom Rauch) wrote:
>On Thu, 08 May 1997 08:44:05 -0600, Lew McCoy <mc...@zianet.com>
>wrote:
>.222222
>>Rick: I have reviewed most of the trap beams during my career and I
>>have found that the Sommer beam is the best by quite a bit, Hy Gain is
>>extremely honest in their gain claims as compared to other
>>manufacturers. I can tell you this and you can take it to the
>>bank--none of the trap beams, regardless on the numbr of element, will
>>exceed 6.2 to 6.5 dbd--that was proven years ago in range measurements
>>and the science has not changed.
>
>Hi Lew,
>Interesting number, but I wonder how that could possibly be true.
>
>If an additional properly tuned element is added and the gain remains
>the same because the loss in the element is so high, why does the
>FIRST additional parasitic element add gain?
>
>When I run 1500 watts to a trap antenna, why don't the traps melt if
>the loss is so high?
Lew doesn't appear to be claiming that trap losses are high, just that
the pattern gain isn't improved as much for trapped elements as it
would be for full size monoband elements. That actually sounds like
an intuitively obvious statement. In other words, the power is still
radiated, it just doesn't go where we want it to go. Thus the traps
may not get hot, but forward gain may not be so hot either.
I can't offer a rigorous explanation why that might be so, but I can
visualize it, and it has a certain intuitive appeal.
Gary
Gary Coffman KE4ZV | You Make It | Email:
Destructive Testing Systems | We Break It | ke...@bellsouth.net
534 Shannon Way | Guaranteed | or
Lawrenceville, GA 30244 | | ke...@radio.org
Fractenna
Lew's point is a good one: Yagis have a practical gain limit--for
reasonable bandwidth. Of course, you can supergain--with poor bandwidth;
rigid construction constraints and so on, and exceed the 6.5 db limit.
Everyone knows that traps are lossy--some more than others. But most hams
don't care about a dB or 2 of forward gain difference , but rather a
decent front to back. A TH6 and a 3 el monobander at the same height will
have very little difference in DXing impact (on 20M for example).
As for a 'critique' of Lew's CQ article, I don't understand why the more
appropriate place and time wasn't in the magazine it was published, in a
reasonable time after it was published. Flaming here only reinforces the
'mean spirited' character for which this newsgroup has been noted.
Is a low height dipole a reasonable comparison for a UNIHAT? Answer:
People do the best they can with the tools they have. I don't seem to
recall anything in that article on how a UNIHAT beats a crafted, super
efficient, home built, top loaded monopole. And isn't that the point?? The
VALUE comes in UNIHAT designing and building such a facsimile of the
beast. All I have to do is buy it and put it up--if that's my bag.
Finally, folded dipoles. Folded dipoles are just fine--if they are
fractally folded. I showed (at the Electronics Industry Forum) last week a
PCS (1940 MHz) fractal folded dipole, 1/5 wave largest dimension, with 60
ohm real impedance, with a field strength of 1.6 dBi. NEC4 simulations,
and S11 return loss on Duroid 4003.
That's within 0.5 dB of a dipole in free space, and VERY efficient. And
VERY cheap compared to slogging on SMT coils, which can't possibly have QF
500 or better at a realistic price. You can't beat that field strength
with real, itsy inductors. Or other end loading methods.
Best to All
Chip N1IR
William E. Sabin
Gary Coffman wrote:
>
>
> Lew doesn't appear to be claiming that trap losses are high, just that
> the pattern gain isn't improved as much for trapped elements as it
> would be for full size monoband elements.
Don't most trap beams also have short (less than optimum) boom length
and also less than optimum element spacing & length arrangement, in
other words poorer directivity on *any* band? They also have narrower
SWR bandwidth, which implies low feedpoint impedance, which implies
lower efficiency (lower ratio of feed Z to loss R). Trap loss is only
part of the picture, maybe not even the most important part.
Bill W0IYH
Tom Rauch
>
>Don't most trap beams also have short (less than optimum) boom length
>and also less than optimum element spacing & length arrangement, in
>other words poorer directivity on *any* band? They also have narrower
>SWR bandwidth, which implies low feedpoint impedance, which implies
>lower efficiency (lower ratio of feed Z to loss R). Trap loss is only
>part of the picture, maybe not even the most important part.
>
>Bill W0IYH
Thank's Bill. That was my puzzlement.
The traps seem to be "getting blamed" for the boom length and tuning.
I wonder if anyone has ever measured trap impedance.
73 Tom
Tom Rauch
Hi Chip,
On 10 May 1997 10:45:14 GMT, frac...@aol.com (Fractenna) wrote:
>Lew's point is a good one: Yagis have a practical gain limit--for
>reasonable bandwidth. Of course, you can supergain--with poor bandwidth;
>rigid construction constraints and so on, and exceed the 6.5 db limit.
Are you, like Lew, saying the upper limit of gain is really 6.5 dBd?
Where can I find that written?
I have seen many end fire antennas that exceed 6.5 dB gain, without
superdirective phasing.
>Everyone knows that traps are lossy--some more than others.
Can you reference some data Chip? Everyone might "know that", but
where is the data? Lew's measurements indicated the pathetic maligned
three element trap yagi had 6.2 to 6.5 dB gain. A full size yagi
would be lucky to make 7 dBd.
Where's the big loss we all hear about? That looks like a half dB or
so loss at best to me.
>But most hams
>don't care about a dB or 2 of forward gain difference , but rather a
>decent front to back. A TH6 and a 3 el monobander at the same height will
>have very little difference in DXing impact (on 20M for example).
Absolutely. You'd never know the difference. Especially if it is half
a dB or so, as the data indicated.
>As for a 'critique' of Lew's CQ article, I don't understand why the more
>appropriate place and time wasn't in the magazine it was published, in a
>reasonable time after it was published. Flaming here only reinforces the
>'mean spirited' character for which this newsgroup has been noted.
Two points Chip.
First, I sent a letter right after the review was published and went
through the trouble of providing references about radiation resistance
and folded monopoles.
Second, this is a technical forum. The beauty and usefulness of this
forum is when a technical statement is made, everyone is free to ask
questions and make comments.
Simple technical disagreements don't make the forum "mean spirited". I
didn't call anyone stupid or dishonest. I am simply questioning a few
statements that were made. While I think the antenna Lew mentioned is
one of the best constructed verticals ever manufactured, the claims
about radiation resistance and efficiency are either incorrect or
greatly exaggerated.
Lew is free (as we all are) to answer technical questions, or supply
data or explainations supporting his claims.
>Is a low height dipole a reasonable comparison for a UNIHAT? Answer:
>People do the best they can with the tools they have. I don't seem to
>recall anything in that article on how a UNIHAT beats a crafted, super
>efficient, home built, top loaded monopole. And isn't that the point??
No.
On page 27 second line. "This gives us a very good radiation
resistance, providing well over 90 percent efficiency on 160- with
better efficiencies on other bands."
The article claims a 31 ft tall ground mounted vertical antenna with
six radials about 30 feet long mounted over natural soil (from page
one of the review) has 90% efficiency on 160.
Do you believe that to be a reasonable claim? How many eff>90%
verticals 1/16 wl high have you seen? Especially when they employ six
.055 wl long radials?
By the way, I didn't bring this up. I was merely replying to Lew. When
I asked a question about the trap yagi, he brought up the review. I
certainly like and respoect Lew, but that doesn't mean I can't ask
questions or disagree with incorrect technical statements.
73 Tom
William E. Sabin
Tom Rauch wrote:
>
> On 10 May 1997 10:45:14 GMT, frac...@aol.com (Fractenna) wrote:
>
> >Lew's point is a good one: Yagis have a practical gain limit--for
> >reasonable bandwidth. Of course, you can supergain--with poor bandwidth;
> >rigid construction constraints and so on, and exceed the 6.5 db limit.
>
> Are you, like Lew, saying the upper limit of gain is really 6.5 dBd?
> Where can I find that written?
>
> I have seen many end fire antennas that exceed 6.5 dB gain, without
> superdirective phasing.
>
> >don't care about a dB or 2 of forward gain difference , but rather a
> >decent front to back. A TH6 and a 3 el monobander at the same height will
> >have very little difference in DXing impact (on 20M for example).
This is not always quite true. A properly designed (computer designed)
monobander will have a better front-to-rear, as compared to
front-to-back. That is, rear side-lobes are better suppressed by
significant dBs. I have not seen any tri-bander specs that good.
Bill W0IYH
Fractenna
Once again Tom, we agree--most of the time.
Did I misunderstand Lew's comment? What would you say is the forward gain
limit of a three element Yagi-Uda? (For one with practical bandwidth for
hams?)
As for trap losses, I have to defer to Joe W1JR. 1/2 dB losses PER TRAP
are typical from his analyses.
As for the 90% efficiency for 1/16 wave.. HAHAHA! You are right; that IS
pretty funny. Sounds like a LORAN or OMEGA antenna! I wasn't responding to
that comment (did you make it?) Is Lew still sticking to his guns on this
one? (I doubt it).
You know how I feel about electrically small antennas...:-)
73
Chip N1IR
Jesse Touhey
On Fri, 09 May 1997 22:45:56 -0600, Lew McCoy <mc...@zianet.com>
wrote:
>> Tekla Oy, Koronakatu 1, 02210 Espoo, +358-9-8879 474Jari and Jesse: You guys are right on. The antennas tested were
>tweaked for maximum gain. The 6. 1 to 6.2--I just examined all the
>charts I have--were for 20 meters. Some of the tests were made on the
>antennas as they came out of the box and some only hit 5 dbd. None of
>were surprised. On antenna, I really should not name but if I get
>pushed enough I might--was checks at minus 2 dbd on 20 meters. Like I
>say--I still have all the charts and graphs and would be happy to answer
>any questions--if I can.
>
>It is no secret but I remember quite clearly about 30 years ago I went
>out to St. Louis to visit Moseley. I asked if I coud see their antenna
>range. They took me up on the roof and across a sea of power lines,
>etc. they said the receiving location "was out there." Nuff said???
>
>Lew McCoy, W1ICP
>
>Lew McCoy, W1ICP
Lew, Why do you want to protect participants on this forum from the
identity of the manufacturers who make false claims? I would
still like to know what company achieved 6.1 - 6.2dbd on 20m with a
tri-band, trap, 3el Yagi. Did you actually participate in those
tests? If so, was the testing done by an independent agency?
You made the statement the Sommers's beam was best by far. Where and
when was these tests done? Who was in charge of the tests? What, was
the comparison antenna, or was this done on a calibrated range? Who
sponsored this test? How many elements are active? How much better
what is the frequency/gain (in dbi)? In your opinion, why is the
Sommers beam "best by far". Lew, when you make an authoritative
statement on this forum you should be prepared to back it up with
technical facts, not hearsay.
You mention your Uni-hat review and Tom Rauch. In your glowing review
of that antenna you attempt to explain the pro and con of antenna
radiation resistance. You make the statement your 180' dipole at a
height of 60' when operated on 160m should have out performed the
vertical! On 160 and 80m that horiz antenna of yours has maximum gain
at 90 degrees....straight up. You go on to say the reason why the
Uni-Hat performs so much better than your 160m dipole (1/8 wl above
ground) and other verticals is the Uni-Hats RADIATION RESISTANCE has
been raised on 160m to 50 ohms. Do you still say the 1/16 WL (160m)
Uni-Hat's radiation resistance is 50 ohms? Do you really believe
inserting a inductance in the negative return of a vertical system
will raise the radiation resistance? How and with what did you measure
the radiation resistance for your review? Or, did you just repeat
what the manufacturer told you to say? You then say the "take-off
angle is 10 degrees". Are you saying maximum gain is at a 10 degree
take-off using six 25' radials? Do you have a salt water lake under
that antenna?
I believe you still retain the Sommers and the Uni-Hat at your qth..
Did you purchase them at list price ($1000 & $499) for the review, or
were they given to you to keep by the Manufacturer? What is CQs and
your policy concerning free reviewed hardware?
Just because it is in writing doesn't make it so.
73, Jesse, W6KKT
JerryL
Fractenna wrote:
<snip>
I showed (at the Electronics Industry Forum) last week a
> PCS (1940 MHz) fractal folded dipole, 1/5 wave largest dimension, with 60
> ohm real impedance, with a field strength of 1.6 dBi. NEC4 simulations,
> and S11 return loss on Duroid 4003.
>
> That's within 0.5 dB of a dipole in free space, and VERY efficient. And
> VERY cheap compared to slogging on SMT coils, which can't possibly have QF
> 500 or better at a realistic price. You can't beat that field strength
> with real, itsy inductors. Or other end loading methods.
>
> Best to All
>
> Chip N1IR
Gee Chip, is that 1.940 mhz or 1940 mhz. If it is 1.940 mhz or could be
sized for a frequency that low I for one would sure like to see the
plans
for that, especially if it will handle a couple of KW !!
regards, Jerry (holding breath..!)
gloc...@lightspeed.net
Phone/Fax (24-hrs) 805-589-4120
David B. Holtkamp (K5KH)
Hi Lew!
Hope you and your family are all doing well...
Thank you for sticking around this newsgroup and offering your opinion.
Many of us value and appreciate your views.
I'm curious -- You are a fan of the Sommer antennas for the reasons
you've mentioned. Do these same reasons carry over to favor Force 12 and
other such antennas? I get the feeling that the Force 12 is similar in
design concept to the Sommer antennas. Is this correct in your view?
Also, have you had a chance to look at the Raibeam antennas?
(http://www.raibeam.com/ for a look)
The Raibeam seem very interesting to me...
Best wishes and hope all is well for you!
David (K5KH)
Fractenna
Jerry--
I don't build anything at millihertz frequencies. Also, the fractal folded
dipole is vertically oriented to give az omni coverage. This may or may
not be what you want.
I'm sure it could be scaled; my time for LF/MF antennas is very limited. I
write an article when I find time (very rare these days) for DX Magazine,
with HF wire antennas in it.
Let's turn the question around: what would your (that is you and other's)
factors be in choosing a folded dipole design for 160M? This will give a
figure of merit, and it would be fun to start from there. In fact, wud
make a great thread: 'Optimized 160M Antennas'. Wanna start?
73
Chip N1IR
Jesse Touhey
Chip, Lew also claims 10 degree take-off using 6 radials!
73, Jesse,W6KKT
Fractenna
Bill--
It might be helpful to others if you define a 'rear' from a 'back'.
Thanks!
Chip N1IR
Tom Rauch
Hi Chip,
On 10 May 1997 19:53:30 GMT, frac...@aol.com (Fractenna) wrote:
>Did I misunderstand Lew's comment?
Let me re-post the comment that confused me again.
Lew said:
>Let's look at gain--a trap beam no matter whose--has a maximum gain for
>6.2 dbd gain--this has been proven many time on qualified range
>measurements. adding more elements does not add more gain--not like a
>straight Yagi.
Unless I need a remedial reading class, that statement indicates a ten
element trap yagi on a 2 wavelength long boom will STILL only have 6.2
dBd gain.
>What would you say is the forward gain
>limit of a three element Yagi-Uda? (For one with practical bandwidth for
>hams?)
Most of the data I've seen places gain at about 6 dBd or so in a
practical monoband three element yagi.
(I have to say I'm in agreement with Bill, the F/B ratio is MUCH more
meaningful than a dB or two of gain. F/B ratio is a good reason to use
properly tuned monobanders.)
>As for trap losses, I have to defer to Joe W1JR. 1/2 dB losses PER TRAP
>are typical from his analyses.
I keep seeing "numbers" but I never find anyone who has supporting
data. If someone sends me a typical trap from any element of a common
trap antenna, I'll be glad to measure it on a Network Analyzer.
From that data, we could use EZnec to estimate the loss when the trap
is used in a real antenna. As I recall Tom Bruhn's measured a coaxial
cable trap, and it had a very good Q factor. Surely a lumped L/C
system could be even better.
How could a carte blanche loss number be correct with so many
variables? Type of trap, trap location on the element, frequency,
which particular element, etc.etc. Current and impedance vary greatly,
so does trap construction. How could it possibly be quantified as "X"
dB loss per trap?
It's like me handing you a resistor, and saying "all resistors have
2.25 dB loss when added to antennas".
>As for the 90% efficiency for 1/16 wave.. HAHAHA! You are right; that IS
>pretty funny. Sounds like a LORAN or OMEGA antenna! I wasn't responding to
>that comment (did you make it?)
Not me. I'm with you on this one. If anyone ever markets a .055 wl
vertical that makes 90% efficiency with 6 .055 wl radials, I'd buy a
few dozen of em, phase them, and throw all my tower away.
9% would easily be possible, but certainly not 90%.
73 Tom
William E. Sabin
I believe I did define it. Front to rear includes all side lobes off the
rear of the beam (90 to 180 to 270 degrees). Front to back refers to
only 180 degrees. This is thoroughly discussed in the recent ARRL
Antenna Books and also in advertising by some beam mfrs such as
Cushcraft. The computer-designed beams emphasize this difference. A lot
of antennas, especially multibanders, that have 30 dB front to back may
only have 25 dB front to rear.
Bill W0IYH
Fractenna
Jesse--
Over sea water :-)?
Chip N1IR
Lew McCoy
William E. Sabin wrote:
>
> Gary Coffman wrote:
> >
> >
> > Lew doesn't appear to be claiming that trap losses are high, just that
> > the pattern gain isn't improved as much for trapped elements as it
> > would be for full size monoband elements.
>
> and also less than optimum element spacing & length arrangement, in
> other words poorer directivity on *any* band? They also have narrower
> SWR bandwidth, which implies low feedpoint impedance, which implies
> lower efficiency (lower ratio of feed Z to loss R). Trap loss is only
> part of the picture, maybe not even the most important part.
>
should. You are right about the OVERALL look at trap antennas. The
engineer must look at the whole picture. Here we have the trap antenna
invented by Buchanan immediately picked up on by the manufacturers and
they quickly produced a three band, three element, trap Yagi beam. I
won't go into details on what they all claimed except to say--and this
is a matter of record in QST--they gave out claims as high as 11 to 12
dbD in their ads until we shut them off.
Here are the problems--the customer--Joe Ham--wants an antenna that will
be of 50 ohm impedance--that is No. 1 on his list--he usually doesn't
give a damn about gain or anything else just so that he has a good match
an very low SWR. The manufacturer is faced with this problem first so
here they have a trap beam with a rather low overall
impedance--relatively tight element spacing but here is the thing that
none of the antenna beam companies wanted to tell us but it is a fact of
antenna life. They had to juggle spacing of elements--length of
elements--etc, to try to get a reasonable bandwidth when they never knew
exactly where the customer--excuse me, not where--but how high that
customer was going to put his beam. Think about that for a minute--how
in heck are they going to satisfy everyone--you and I know that the only
way is to build a dummy load and then you can put it anywhere and it
will be a "match." For Tom's benefit I am NOT saying that all trap
beams are a dummy load--although some of them mught well be. In any
case, that was and is one of the goals. Now keep in mind that in order
to get his broadband, match on several bands--you must juggle element
lengths, spacing, etc.--And Oh Yes, don't overlook the fact that short
boom lengths sell better than long boom lengths.
So what do we end up with? The customer says hey you guys I want my
traps shielded and protected or I won't buy your antenna! So the
manufacturer does just that--he shields the stupid things making them
lossy devices.
Now we get to what I wrote about on the antenna measurements. I still
have some confidences to respect because jobs may be at stake but I did
go though a long series of trap beams and other beams tests some years
back--the science has not changed since those tests. The arguments
came about because the beam manfacturers want to change or have QST
permit gain measurements and that was one reason for the tests.
Needless to say it didn't change the technical department at ARRL's
thinking one bit--I cannot say what there policy is today but I am
always getting slammed for being critical of that organization in todays
market.
In any case, getting back to the tests, many beams were tested for gain,
front to back, front to side, etc. I have said so before so I don't
mind repeating it--one popular trap beam actually showed -2dBd. None
of the trap beams even approached a single well tuned 3 element
monibander.
I know that Tom was critical of my remarks but then again Tom seems to
be critical of anything I say. All I can say to him is he might want to
look up the formula for effective area of an antenna (not CAPTURE AREA)
there is no such thing. You'll find the formulas on page 25-41 of
"Reference Data For Radio Engineers". Incidentally--when I hear or see
antenna men talking about "Capture Area" I immediately put them in a
nondescribed class of engineers because they simply are spouting. And,
and this is important--they may claim to be experts but what they are
saying shows they ain't.
I won't be around after Monday--I am off to Fayton.
You guys all have fun.
Lew McCoy, W1ICP
So let me wind this up--whenever you reduce the size of antenna--you
reduce the effective area and the antenna has less gain. This happens
with all trap antennas--I really think the antenna manufacturers know
all this but again --the customer wishes are the bottom line.
]
William E. Sabin
Lew McCoy wrote:
>
> William E. Sabin wrote:
> >
>they gave out claims as high as 11 to 12
> dbD in their ads until we shut them off.
>
I believe some vendors like to include the gain at some optimum
elevation angle due to ground reflection enhancement, which is dirty
pool and misleading. A dipole also has a similar enhancement, as I
understand it.
Bill W0IYH
Jesse Touhey
Hi Chip, think about it. In real world, I know of no other way a
single element ground mounted vertical operated on the lower bands,
using six 25' radials, can achieve maximum gain at a 10 degree
take-off. Do you? He also claims the 160m, 1/8 WL, ground mounted
vertical (6- 25' radials) has a "50 ohm radiation resistance"
(Uni-Hat, Dec 94 CQ).
Respectfully, Jesse, W6KKT
Richard Clark
Hi Lew,
In spite of you're having said this all once before, in parts or
together, the hobgoblins of consistantcy are vexing you. None too
surprising here in the group where if we can't find techical fault we
mine the punctuation for a couple of dB loss.
When push comes to shove, Lew, let's give them each a room to proclaim
their versions of the truth at Dayton and see which room fills up
faster. I'm sure that attendance at your presentation will prove both
the range of your experiance and the acknowledgement of your years of
service. I hope to be among them if timing works out.
73's until then,
Richard Clark, KB7QHC
Fractenna
But Bill, it won't be '11 dBd' as the 'd(ipole)' will also be enhanced to,
say, 8dBi. That means the antenna would be *******19dBi********* Yikes!
Love them l-a-r-g-e apertures. Hi!
Or are you saying that when people say X dBd they mean compared to the 2.1
dBi of a free space dipole (with no loss)?
Better to avoid the dBd entirely...
Just wondering.
Chip N1IR
Roy Lewallen
In article <337604...@zianet.com>, Lew McCoy <mc...@zianet.com> wrote:
>. . .
>So let me wind this up--whenever you reduce the size of antenna--you
>reduce the effective area and the antenna has less gain. This happens
>with all trap antennas--I really think the antenna manufacturers know
>all this but again --the customer wishes are the bottom line.
Reducing the size of an antenna doesn't automatically reduce its gain. In
fact, you can change the gain of antenna significantly by doing nothing to
its size. For example, in Chapter 8 of the _ARRL Antenna Book_, there are a
couple of pages of patterns of two-element phased arrays. With 1/2
wavelength spacing, you can change the gain from 2.3 to 3.8 dB (relative to
a single element) just by changing the phasing. Assuming negligible loss (a
good assumption for, say, 1/2 wavelength dipole elements), the effective
area changes in proportion.
Now, I can change the spacing to 1/4 wavelength, making the antenna
smaller, and get up to 4.5 dB gain (relative to a single element), with
attendent greater effective area. (It'll be a little harder to keep the
loss negligible, but I bet I could make an antenna with greater gain (and
effective area) at 1/4 wave spacing than at 1/2, using 1/2 wavelength
dipole elements.)
I know this won't convince Lew, because I've tried before. But maybe some
of the other readers will be prompted to look into it a little more
thoroughly.
Roy Lewallen, W7EL
Roy Lewallen
In article <3375c6ec...@netnews.worldnet.att.net>,
W8J...@worldnet.att.net (Tom Rauch) wrote:
>. . .
>I keep seeing "numbers" but I never find anyone who has supporting
>data. If someone sends me a typical trap from any element of a common
>trap antenna, I'll be glad to measure it on a Network Analyzer.
>From that data, we could use EZnec to estimate the loss when the trap
>is used in a real antenna. As I recall Tom Bruhn's measured a coaxial
>cable trap, and it had a very good Q factor. Surely a lumped L/C
>system could be even better.
>
>How could a carte blanche loss number be correct with so many
>variables? Type of trap, trap location on the element, frequency,
>which particular element, etc.etc. Current and impedance vary greatly,
>so does trap construction. How could it possibly be quantified as "X"
>dB loss per trap?
I've done a little modeling of trapped antennas, but not with traps
representing state-of-the-art for loss. They're traps I've made with RG-58.
As I recall, effective inductor Q was around 200 (I can check). The
interesting thing is that significant loss occurs only with certain
combinations of bands. Typically, the traps will show low loss on all bands
but one, and this is when certain combinations are used. For a three-band
Field Day dipole, I use a two-band trap antenna with a dipole for a third
band hung under it (but connected to the same feedpoint) as an inverted
vee. I did this because the 3-band combination with traps I can easily make
had too much loss on the third band. On the band where significant loss
occurs, 2 dB is a typical value for the traps I construct.
Tom's absolutely right that you can't assign a single loss value to traps.
It depends not only on the trap construction, but the lengths of wire it's
connected to (which determine the voltage across and current through it),
and the frequency of operation.
If you measure traps, Tom, make sure you simulate the potential
shorted-turn effect of attached tubing.
Roy Lewallen, W7EL
Fractenna
Jesse--
'Smiley' sez its not worth thinking about...you missed it.
Chip N1IR
William E. Sabin
Roy Lewallen wrote:
>
>
>
> Reducing the size of an antenna doesn't automatically reduce its gain. In
> fact, you can change the gain of antenna significantly by doing nothing to
> its size.
This discussion so far has related to the triband Yagi, only. Apples and
oranges belong in two different bushel baskets.
Bill W0IYH
Tom Rauch
Hi Chip,
dBd is a good method. It's dBi that results in the inflated gain
figures, like 12 dB or more. It would be best if comparison
measurements were properly made using dBd.
On Mon, 12 May 97 08:25:43 GMT, w7...@teleport.com (Roy Lewallen)
wrote:
>Reducing the size of an antenna doesn't automatically reduce its gain. In
>fact, you can change the gain of antenna significantly by doing nothing to
>its size.
As Roy points out, this is a common misconcepion. Even Lew stated
making an antenna smaller reduced "effective aperture". The truth is,
physical size does not directly tie into the effective aperture. It
would be nice if the capture area myth disappeared.
A physically large antenna can easily have a much smaller effective
aperture than a small antenna, or vice versa.
>For example, in Chapter 8 of the _ARRL Antenna Book_, there are a
>couple of pages of patterns of two-element phased arrays. With 1/2
>wavelength spacing, you can change the gain from 2.3 to 3.8 dB (relative to
>a single element) just by changing the phasing.
The measurements Lew "quoted" were taken at one wave angle. If the
wave angle selected was NOT in the center of the main lobe ALL of the
comparisons in the readings are meaningless. A more directive array
could easily show less "gain". All we know for sure is at whatever
wave angle (I believe it was zero degrees) the antennas tested beat a
reference dipole at the same height by about 6 dB.
Actually 6dBd gain is very GOOD for a three element antenna, although
it could have been skewed in favor of the yagi by the improper
measurement method.
More than anything. the posted results convinced me a TH6 is great
antenna.
>Now, I can change the spacing to 1/4 wavelength, making the antenna
>smaller, and get up to 4.5 dB gain (relative to a single element), with
>attendent greater effective area. (It'll be a little harder to keep the
>loss negligible, but I bet I could make an antenna with greater gain (and
>effective area) at 1/4 wave spacing than at 1/2, using 1/2 wavelength
>dipole elements.)
That's a good point many of us miss. SMALLER spacing in end-fire (i.e.
the yagi) increases effective aperture (sometimes called capture area
in amateur circles) as long as losses don't become excessive.
>I know this won't convince Lew, because I've tried before. But maybe some
>of the other readers will be prompted to look into it a little more
>thoroughly.
Trap antennas have been given a bad reputation, mostly from
manufacturer's advertisements and propaganda traps are "lossy".
One large antenna manufacturer asked me to design a multi-band yagi.
When I suggested trying lumped traps in a comparison antenna to reduce
wind load and improve performance they rejected the idea completely.
The reason given was even IF adding a few traps made the antenna
perform better or weigh less and have less wind load for the same
area, marketing an antenna with a trap would be difficult because the
reputation of traps has been thoroughly ruined by marketing hype.
It's a shame amateurs are steered out of considering some good
antennas because of marketing hype and rumors.
73, Tom
Lew McCoy
> >
> >limit of a three element Yagi-Uda? (For one with practical bandwidth for
> >hams?)
> >
> >are typical from his analyses.
> >
> >pretty funny. Sounds like a LORAN or OMEGA antenna! I wasn't responding to
> >one? (I doubt it).
> >
> >You know how I feel about electrically small antennas...:-)
> >
> >
> >73
> >Chip N1IR
>
> Chip, Lew also claims 10 degree take-off using 6 radials!
> 73, Jesse,W6KKT
Jesse: I am beginning to think I won't be around long enough to discuss
or argue with you guys--just spent the night in emergency with severe
pains--fortunately--it was not my ticker. Let me say a few things about
that short vertical--the UniHat. Ed Goodman, one of the the
designers--has been building these things for a long time know and many
of them are in use at A-M broadcast stations. In addition, they have
been extensively tested agfainst full size, quarter wave verticals. As
I recall--and this is an approximate statement--if there is such a
thing--they came with in 80 to 90 percent of the halfwave on field
strength. But that is not the bottom line by any means. Un til you
have tried this antenna--you should not make judgements. AS couple of
friend on mine have put them up and they have had absolutely outstanding
results. We can argue over impedance, ground conditions, etc. until
hell freezes over but until you use one--you really have no right to
judge. It is easy to say that theory says this or that but to me--and
this is after scores and scores of antenna testing--until you use the
darn things you have to be careful what you say. One other thing about
the UniHat--It is very good antenna on 80 and 40--it does a fantastic
job against on low angle stuff on 40.
And while I am at it--some character--and I cleaned up the word
character--made a remark of do we "buy" the antennas we test? To me
that is an utterly dumb statement with its implications. Since antenna
testing began and product reviews have been written--anyone--and I mean
ANYONE who puts up any antenna--does all the construction and
erection--can keep the antenna if he or she so desires--that was League
policy and is also CQ policy. The manufacturer is told that before he
ewven ships the antenna for review. Of course, the question can
arise--how honest is the review because supposedly he is getting the
antenna for zilch dollars? Well--I cannot speak for other reviewers but
I can guarantee you that I have refused to review many beams and other
"antennas" simply because I kn ew they were dogs before even going
farther. You do not know this but in my case--I have nearly been fired
by both QST and CQ for simply refusing to do articles about stuff that
is junk. So here is the bottom line--what I have just said is about
antennas--not anything else. Writers will sometimes get a much better
deal if they want to buy the gear after testing but that is an
individual thing. I could write a whole series on here of what a ham
should be aware of--would you like to see such a series--I know damn
well that QST and CQ wouldn't like it--hi!
Lew McCoy, W1ICP
Roy Lewallen
In article <33762D...@crpl.cedar-rapids.lib.ia.us>,
Yes, a dipole has essentially the same enhancement at a given height as a
Yagi. This seems to hold at least for Yagis with a moderate number of
elements -- I haven't looked at Yagis over 5 elements. The manufacturers
take advantage of the widespread misconception that dBd means "dB relative
to a dipole at some height", while it's universally used to mean "dB
relative to a dipole in free space" (hence the common relationship that
dBd = 2.15 + dBi). It's not difficult to get 4-5 dBd gain from a dipole
mounted over ground.
Roy Lewallen, W7EL
Cecil Moore
Lew McCoy wrote:
> Trouble is about that "elevation angle" the manufacturers never did
> really understand that aspect or the problem or their lies would have
> been even greater. 73 Lew, W1ICP
So Lew, EZNEC sez my G5RV has a 10 dBi gain on 12m. What is it's gain
in dBd? :-)
73, Cecil, W6RCA, OOTC
Fractenna
Hi Tom--
Yet once again we (almost) agree.
I would have to say that as I deal with more pro antenna guys, they
continually pose the dBd as a point of ridicule, as in 'those in the know
say 'no' to dBd'.
You may buck the trend if you like; certainly I find times when it's more
meaningful to use dBd myself.
Wud be interesting to take a poll on use of dBd.
73
Chip N1IR
Fractenna
Probably about 2 dbd Cecil.;-)
Chip
Fractenna
Lew--
I'm sure the UNIHAT is a great antenna for what it's designed for. However
at 1/16 of a wave, it's radiation resistance will be a few ohms at best.
I'm sure the ohmic losses are greater than an ohm, ergo efficiency won't
be 90%.
However, top loading is an acceptable way of getting good efficiency and
this was apparent to me from the ads that that's what was sought. I would
bet the antenna is about -1 to -3 dBi over real ground, which is pretty
good on 160M, especially with a reasonably low launch angle.
Ten degrees launch angle sounds a little low; bet its closer to 20 degrees
with a typical ground in the US. Put it over sea water with raised radials
and I bet that launch angle will be nice and low though.
Hey--I think its a nice antenna. Sorry the discussion got a little
pedantic and spiteful.
Sounds like the fractal threads! :-)
As for Jesse's comment on keeping stuff. HAHAH!! As if columnists get
rich!
73
Chip N1IR
Roy Lewallen
In article <5l7lvv$no0$3...@nadine.teleport.com>,
w7...@teleport.com (Roy Lewallen) wrote:
>In article <33766bee...@news.seanet.com>,
> rwc...@rwclark.seanet.com (Richard Clark) wrote:
>Sounds like a good way to determine which facts are correct. I'd lay
>money that Princess Di would draw even a bigger crowd and therefore have
an
>even better handle on the gain of triband beams. If they could book her,
>guess you'd have to listen to her explanation instead of Lew's.
>Roy Lewallen, W7EL
I'm afraid I tried to be a bit too subtle and failed to communicate. Some
email correspondence indicates this was taken as a criticism of Lew or his
statements about triband beams. It was not. It was intended as criticism of
Richard's proposal for a way to determine facts. I'm sure Di would pack a
room a lot fuller than I would, too, so by his criterion she also knows
more about triband beams than I do. (Which in this case might well be
true!)
I have opinions, but I don't have any facts or experience that disagree
with or support what Lew or anyone else has said here about triband beams.
So I'm not commenting on his or other people's statements on the topic. I'm
listening and learning like a lot of other folks.
Roy Lewallen, W7EL
Roy Lewallen
Tom Rauch
On Mon, 12 May 1997 11:17:00 -0600, Lew McCoy <mc...@zianet.com>
wrote:
>designers--has been building these things for a long time know and many
>of them are in use at A-M broadcast stations. In addition, they have
>been extensively tested agfainst full size, quarter wave verticals. As
>I recall--and this is an approximate statement--if there is such a
>thing--they came with in 80 to 90 percent of the halfwave on field
>strength.
That's a very well built antenna, but unfortunately relying on a
manufacturer's claim in a review isn't always the best idea. I think
that's what got you in the soup on this one Lew.
The radiation resistance claims are fiction. The hat increases the
loop radiation resistance, but the folded wires only change the
impedance seen by the feedline. You certainly should realize that
after the long thread here on the antenna newsgroup on radiation
resistance.
The net current flowing into the earth is about the same as any other
antenna of the same height with the same size hat, and because current
is the same ground losses are not reduced by the folded wires. It is
an absolute fact ground losses occuring from induction fields, from
direct connections, or from radiation fields are NOT changed by
changing the feedpoint method.
As to the measurements, when I called Los Alamos and talked to them
(and I repeated this exercise again last week), they said they had "no
real antenna test range". Neither the physics departments or
communications departments were aware of any real test range at their
facility.
A few years ago, when I called Los Alamos, I spoke with RB Wheeler,
who (he is a technician at Los Alamos) was aware of the antenna. He
said the field strength measurements were made at a Ham's house with
the antenna located on on top of a mesa. The measurements were
purported to be relative measurements only. As a matter of fact, last
week the telecommunications area at Los Alamos told me they could only
do relative FS measurements, since they lack the equipment and range.
It's also worth noting Mr. Wheeler agreed the radiation resistance
claims were non-sense.
So you see, wild claims are common Lew. It's just not the 12 dB trap
yagis that engage in this.
The contra-wound toroid antenna is marketed as an "efficient antenna",
and the very small Cross-field antenna claims it is "more efficient
than full sized antennas". After all the smoke clears, these antennas
all turn out to be no magic at all. They are just as (in)efficient as
any other antenna the same size.
While I have little doubt the antenna you tested might have
outperformed a low dipole 180 feet long, that is not much of a test.
Nearly any half-way decent vertical will beat a 60 ft high 180 ft long
dipole on 160. It's pretty hard to tell if you have 5 or ten dB of
loss, unless you have a good reference antenna.
Without an extensive ground system, ANY 31 foot tall vertical would be
a poor antenna for 160. It certainly might be better than another poor
antenna, but it would be no better than a $15 dollar inverted L the
same height with the same ground system on that band.
On the subject of reviews, I've found QST to be very independent of
anything a manufacturer says. That certainly is NOT the case with
other publications. By far the most impartial reviews come from QST,
although everyone makes a mistake or gets in a dispute once in a
while. Most other reviews are just repeats of data supplied by the
manufacturer, so they are more like glorified ads than true reviews.
73, Tom
Jesse Touhey
>> 73, Jesse,W6KKT
>
>Jesse: I am beginning to think I won't be around long enough to discuss
>or argue with you guys--just spent the night in emergency with severe
>pains--fortunately--it was not my ticker. Let me say a few things about
>that short vertical--the UniHat. Ed Goodman, one of the the
>designers--has been building these things for a long time know and many
>of them are in use at A-M broadcast stations. In addition, they have
>been extensively tested agfainst full size, quarter wave verticals. As
>I recall--and this is an approximate statement--if there is such a
>thing--they came with in 80 to 90 percent of the halfwave on field
>strength. But that is not the bottom line by any means. Un til you
>have tried this antenna--you should not make judgements. AS couple of
>friend on mine have put them up and they have had absolutely outstanding
>results. We can argue over impedance, ground conditions, etc. until
>hell freezes over but until you use one--you really have no right to
>judge. It is easy to say that theory says this or that but to me--and
>this is after scores and scores of antenna testing--until you use the
>darn things you have to be careful what you say. One other thing about
>the UniHat--It is very good antenna on 80 and 40--it does a fantastic
>job against on low angle stuff on 40.
>Snip Snip
>
>Lew McCoy, W1ICP
Hi Lew, I, and I know, everyone else want's you around for a long,
long time.
You, not Goodman, is the one who wrote, was reimbursed, and is
responsible for the glowing, if technically inaccurate, Uni-Hat
article. Your "icon" was at the letter head.
In that article you state "This gives us a very good radiation
resistance, providing WELL OVER 90 PERCENT EFFICIENCY ON 160."
After much discussion on the merits of high radiation resistance you
write: "the radiation resistance on 160 is right at 50 ohm, making it
a very efficient antenna on 160 and other bands." You also state the
measured take off angle is 10 degrees. In my opinion, all of the
above is pure HOG WASH! After comparing the antenna with a very poor
160 and 80m horiz high angle dipole (you said it should have beat the
Uni-Hat) you gave your glowing endorsement to that $500 short
vertical with a large capacity hat. Anyone who makes the statement
the Uni-Hat provides "well over 90 percent efficiency on 160", has a
50 ohm radiation resistance, and gives max gain at a 10 degree take
off angle using 6- 25- radials, is repeating a joke his barber told
him, or simply doesn't understand the subject matter he's writing
about.
Lew, in all your descantings and prose have you ever admitted to being
wrong, or not understand something? Or, does the title "CQ technical
editor" afford you immunity from all that? Are you related to that guy
in the white house? I'm serious!
The person who thinks he knows it all.....knows little.....and....will
most certainly learn nothing new, and go through life just repeating
what others have done..
73, Jesse, W6KKT
Chuck (Jack) Hawley
> >Jesse: I am beginning to think I won't be around long enough to discuss
> >or argue with you guys--just spent the night in emergency with severe
> >pains--fortunately--it was not my ticker. Let me say a few things about
> >that short vertical--the UniHat. Ed Goodman, one of the the
> >designers--has been building these things for a long time know and many
> >Snip Snip
While I agree with Jesse in everything he said (and I would imagine that
a lot of silent others agree also), I was affected by your emergency
room visit. Don't let the debates give you additional stress.....just
relax and join in. I (and I'm sure others) like and enjoy you even when
you are wrong....maybe you are right and just don't know why.....maybe
you remind us of our Dads.....heh, heh.
73,
Chuck.
--
Charles (Jack) Hawley Jr.
Amateur Radio: Chuck, KE9UW
BMW Motorcycles: Jack, BMWMOA #224
c-ha...@uiuc.edu
Sr. Research Engineer Emeritus
University of Illinois, Urbana-Champaign
Fractenna
I agree Jesse; if you DO use dBd it strongly implies comparison to a
dipole in the same conditions.
Ask around though-- the pro's and academics seem to avoid dBd.
I use it when I compare to a dipole in the same conditions.
73
Chip N1IR
Jesse Touhey
On Tue, 13 May 1997 08:02:34 -0500, "Chuck (Jack) Hawley"
<c-ha...@uiuc.edu> wrote:
snip
>Jesse Touhey wrote:
Hi Charles, I couldn't agree more...You are absolutely correct
concerning Lew's health. After all, most of this stuff is
theoretical, seldom proved, and will mean nothing when we meet the
"Master Antenna Designer in the sky". The wonderful thing about this
forum is an unsound statement or theory will go not long un-punished.
I put myself at the top of the list for being wrong the most. Out of
self preservation one is really motivated to try and get their posts
correct for fear of the corrective retribution. God! I hate to admit
it when I'm wrong. And, I really hate it when I'm caught!
All of this is a real adrenalin rush!
Respectfully, Jesse, W6KKT
Jesse Touhey
Chip, I agree. If in one of your writings you stated the gain of your
antenna was 8dbd, I would assume you conducted gain measurements with
your antenna, took it down, replaced it with a dipole, and measured
the best possible gain of the dipole. It never would have occurred to
me the comparison dipole would be a theoretical one in free-space.
73, Jesse, W6KKT
MERVW2OE
Chip, Jesse, I wish it were true that gain figures shown as dBd were
compairsons between two antennas in the same environment. Unfortunately
it appears that quoted dBd gain figures normally compare a dipole in free
space against the subject antenna at some unknown height above some
(again unknown) ground.
A look at a couple of models seems to bear this out. Using AO, for
optimization and ELNEC for confirmation. I designed and optimized a 40
meter 3 element yagi to sit 64 feet above average ground. Per the models
the antenna has a dBd gain of 10.04. Also per the models a resonant
dipole at 64 feet has a dBd gain of 4.73. Thus the yagi is 5.31 dB better
than the dipole in the same location. (All gains at a 26 degree elevation
angle.)
Looking at the same yagi model in freespace the model shows a gain of 5.74
dBd. Not exactly the 5.31 shown above, but close.
BTW, I also built and installed the above yagi - I don't know how much
gain it has, but it does kick butt.
Regards, Merv
Lew McCoy
should be the dbd for comparison--maybe not exact but all things taken O
would say about 7.8 dbd in whatever directions eznec says for 10 dbi.
Lew McCoy, W1ICP also OOTC
Roy Lewallen
In article <19970512180...@ladder01.news.aol.com>,
My feelings about dBd are elaborated in a section in the EZNEC and ELNEC
manuals titled "Why Not dBd?" Briefly, the problem with dBd is that people
tend to think it refers to the gain of a dipole over ground, which it
doesn't. It refers to the gain of a dipole in free space, which is just as
ficticious an antenna as an isotropic radiator.
In my opinion, dBd is useful for a very narrow class of antenna, including
the Yagi. If you put a Yagi in your back yard up, say, 50 feet and
compare it with a dipole also at 50 feet, the gain you'll see is close
to the FREE-SPACE gain of the Yagi in dBd. This isn't true of many other
types of antenna. I saw a Force 12 flyer which gives the gain of their
Yagis over ground in dBd. The only purpose I can see to do this is to
mislead people -- as I've mentioned before, the gain of a dipole over
ground is typically 4-5 dBd. (They did include the free-space value as
something like "effective gain" or some such. In my opinion it would have
been more honest to label this "Real Gain" and the gain over ground as
"Gain Intended To Mislead You".)
You can always convert between dBd and dBi simply by adding or subtracting
2.15 dB, so in theory, one is as good as the other. But when I say that my
vertical has a gain of -2 dBd, what does it mean? Does it mean that the
gain of my vertical is 2 dB less than a dipole in my back yard? Absolutely
not! It's certainly no more useful than the equivalent in dBi, and will be
understood by people who don't know the meaning of dBd.
If you want to know what the gain of your antenna (say, a vertical) is
relative to a dipole in the back yard, first model a dipole in the back
yard. Record its gain IN THE DIRECTION(S) AND ELEVATION ANGLE(S) OF
INTEREST in dBi or dBd -- it doesn't matter which. Then model your other
antenna and do the same, using the same reference (dBi or dBd). Then
subtract the two to find the difference in dB. Better yet, construct both
and switch between them when listening to signals from a variety of
directions and distances.
I have a problem with the emphasis on gain, and a single gain value for a
given antenna. It's entirely appropriate for Yagis where you can point the
antenna wherever you like. But if you can't, who cares what the "gain" is
if it's in the wrong direction? The gain is different in all directions --
its graph is the antenna pattern. If all that counts is the gain in one
direction, we wouldn't have any need for all those patterns. Be wary of any
data-reducing terms, like "gain" (when used as a single number for an
antenna) or "average". Remember the statistician who drowned crossing a
creek whose average depth was only 3 feet!
Put me down in favor of dBd for FREE-SPACE gain of Yagis and a few other
horizontal, dipole-like antennas or arrays*, and dBi for everything else.
Roy Lewallen, W7EL
*If I mount the antenna in my back yard and compare it with a dipole at the
same height, the gain difference should be nearly the antenna's free-space
gain in dBd. If this isn't true, dBd is inappropriate.
Tom Rauch
On Tue, 13 May 1997 14:26:27 GMT, w6...@frazmtn.com (Jesse Touhey)
wrote:
>Hi Charles, I couldn't agree more...You are absolutely correct
>concerning Lew's health. After all, most of this stuff is
>theoretical, seldom proved, and will mean nothing when we meet the
>"Master Antenna Designer in the sky". The wonderful thing about this
>forum is an unsound statement or theory will go not long un-punished.
>I put myself at the top of the list for being wrong the most. Out of
>self preservation one is really motivated to try and get their posts
>correct for fear of the corrective retribution. God! I hate to admit
>it when I'm wrong. And, I really hate it when I'm caught!
>All of this is a real adrenalin rush!
>
>Respectfully, Jesse, W6KKT
Hi Lew, Jesse and Charles,
I also hope no one takes any technical disagreement personally, or
lets the truth bother him too much. Technical issues are technical
issues, and have nothing to do with the quality of any of us as
individuals.
We all learn the most when we make mistakes, and nothing at all when
we are correct. Learning is the biggest blessing of life (when I was
young I had other priorities :-) .
At least I've found that to be true, hi.
73 Tom
Tom Rauch
On Tue, 13 May 1997 15:06:33 GMT, w6...@frazmtn.com (Jesse Touhey)
wrote:
>
>Chip, I agree. If in one of your writings you stated the gain of your
>antenna was 8dbd, I would assume you conducted gain measurements with
>your antenna, took it down, replaced it with a dipole, and measured
>the best possible gain of the dipole. It never would have occurred to
>me the comparison dipole would be a theoretical one in free-space.
>73, Jesse, W6KKT
I'm puzzled by this also. I have always used, and recall seeing used,
a dipole under the same conditions used as the reference.
If it is a free-space dipole then the reference is no better than dBi,
because any free space gain figure tells us little or nothing about
the antenna's performance in the real world.
This is a lot like radiation resistance, the defintions and standards
police need to visit the antenna people more often.
73, Tom
73, Tom
dick sander
Referencing gain vs Front-to-back:
|But most hams
|don't care about a dB or 2 of forward gain difference , but rather a
|decent front to back. A TH6 and a 3 el monobander at the same height will
|have very little difference in DXing impact (on 20M for example).
From W8J...@worldnet.att.net (Tom Rauch)
Newsgroups: rec.radio.amateur.antenna
Subject: Re: Triband opinions
Date: Sat, 10 May 1997 18:58:49 GMT
Tom stated:
|Absolutely. You'd never know the difference. Especially if it is half
|a dB or so, as the data indicated.
Tom when we're on 20m (I'm in Texas and you're in Ga) and a rare European
appears and the pileup begins. I guarantee you I don't care about F/B.
Only gain! ERP wins pileups -on any band. Regardless if my antenna is a
beam or vertical. I'll take 1 dB gain any day.
Because from the DX side, everything they hear is at a level that I call the
"QRM floor". So for me gain is important; to get over the boys that tuned their
beams for F/B. I'm just setting the record straight :)
73 Dick -K5QY
MERVW2OE
Chip, you're right. ELNEC uses dBi, as does NEC4WIN; however, AO uses
dBd. I noticed that that one of the instruction models Roy ships with
ELNEC is a dipole in free space, which shows a gain of 2.149 dBi. I am
assuming this is a hardcoded constant. Regards, Merv
Fractenna
Yeh, point well taken Merv. I AM confused though--aren't the ELNEC results
in dBi?? Perhaps I've been ignoring the 'dBd' toggle and deriving the dBd
values myself! :-)
73
Chip N1IR
Tom Rauch
On 13 May 1997 16:04:54 GMT, san...@aud.alcatel.com (dick sander)
wrote:
>Tom when we're on 20m (I'm in Texas and you're in Ga) and a rare European
>appears and the pileup begins. I guarantee you I don't care about F/B.
>Only gain! ERP wins pileups -on any band. Regardless if my antenna is a
>beam or vertical. I'll take 1 dB gain any day.
>
>Because from the DX side, everything they hear is at a level that I call the
>"QRM floor". So for me gain is important; to get over the boys that tuned their
>beams for F/B. I'm just setting the record straight :)
>
>73 Dick -K5QY
Hi Dick,
I stuck my foot in a subjective opinion.
I never care about one dB gain, because my problem is ALWAYS hearing
the DX station reply through the mess of other stations calling him,
and having a ragchew without stateside stations QRMing the DX.
I can easily make up for the one dB by turning up the wick, but there
is no way I can make the receiving situation get better without the
antenna having a clean and deep null.
We'll have to agree to disagree on this, since it is subjective.
73 Tom
Fractenna
Jesse--
Yes; (when) I have used dBd and it was always in the context of the dipole
in the same environment.For example, on the 'Cohen' dipole model values
(an echelon/collinear fractal dipole) I state gain as dBd in free
space--both antenna and dipole. Obviously the free space gain is the free
space gain...
73
Chip N1IR
David B. Holtkamp (K5KH)
Tom Rauch <W8J...@worldnet.att.net> wrote in article
> As to the measurements, when I called Los Alamos and talked to them
> (and I repeated this exercise again last week), they said they had "no
> real antenna test range". Neither the physics departments or
> communications departments were aware of any real test range at their
> facility.
Tom, as you might remember, I live/work in Los Alamos and can confirm
that this antenna is not located in any site that would lend itself to
"antenna range" - type measurements. Too many nearby structures/antennas,
etc.
One point worth noting in this discussion, however, is the unusual
properties of the ground up here. I live about 10 mi away from where the
antenna you mentioned is sited, but the composition of the mesas around
here are quite similar. They are compacted volcanic ash (called "tuff")
that seems to have a remarkably low dielectric constant.
Qualitatively I can attest to this because I have a "double" G5RV that
snakes its way from my 35' tower across the house one way and down to and
along a wooden fence -- the other way it goes down at 45 deg. to about 4'
off the ground and goes along a wooden fence for about 1/2 of its length.
If you ever check into the 3905 Century Club on 160m, you'd hear me for
sure. The configuration is a noisy one, but really does seem to get out
well. Perhaps the low dielectric constant of the soil puts my ground
several hundred ft down ( the water table is near the altitude of the
nearby Rio Grande river - approx 1000 ft down relative to my location). I
seem to get out better than I have any reasonable right to expect given
heights, etc.
So I wonder if no ground for 100' down is as good as a great ground and
tall tower? <smile>
Best wishes,
David (K5KH)
William E. Sabin
Cecil Moore wrote:
> By Jove Merv, You're onto something. We'll measure our antennas in
> kB's from now on (kick Butts).
From now on, dB means deciButts, in memory of the right honorable Earl
of Buttingshire, inventor of the trap rotary beam antenna that has 12
deciButts of *honest* (no baloney) forward gain.
Bill W0IYH
Jesse Touhey
On Mon, 12 May 97 17:58:54 GMT, w7...@teleport.com (Roy Lewallen)
wrote:
>In article <33762D...@crpl.cedar-rapids.lib.ia.us>,
Roy, do you have reference as to when dBd started being "universally
used to mean dB relative to a dipole in FREE-SPACE". Why would anyone
desire to muddy the waters further with two theoretical antennas
(isotropic and free-space dipole)?
When gain comparison figures have been given in dBd I have
interrupted that to mean: Compared with a Dipoles best gain, at the
same height, over the same medium, and with the same polarization.
This could be over earth, or free-space as long as both antenna's use
the same medium. In the 15 edition, ARRL ANTENNA BOOK (page 2-22)
they go on to say: "In practice, measurements on the antenna being
tested are usually compared with measurements made on a 1/2 WL dipole.
The dipole should be at the same height and have the same polarization
as the antenna under test, and the reference field- that from the 1/2
WL dipole comparison antenna - should be measured in the most favored
direction of the dipole" Ironically, though used extensively in the
their books (ARRL) I find no mention of dBd in their Glossary! Roy,
please point me in the right direction.
Respectfully, Jesse, W6KKT
Cecil Moore
MERVW2OE wrote:
> BTW, I also built and installed the above yagi - I don't know how much
> gain it has, but it does kick butt. Regards, Merv
By Jove Merv, You're onto something. We'll measure our antennas in
kB's from now on (kick Butts).
73, Cecil, W6RCA, OOTC
Cecil Moore
Lew McCoy wrote:
> I would say about 7.8 dbd in whatever directions eznec says for 10 dbi.
Wow, my G5RV has a gain equal to a lot of Yagi's. I guess this is how
antenna manufacturers play games with gain. dBd seems to be rather
nebulous. I remember reading about this $500 LP that had an advertised
gain of 8dBi. Hope that was in free space.
73, Cecil, W6RCA, OOTC
David B. Holtkamp (K5KH)
Lew McCoy <mc...@zianet.com> wrote in article <33774B...@zianet.com>...
> > Also, have you had a chance to look at the Raibeam antennas?
> > (http://www.raibeam.com/ for a look)
>
Lew, thanks for the reply! Yes, indeed, I imagine that the inline
elements can significantly affect both patter and gain.
Ummm...I'm still curious about the Raibeam antennas, though. I assume
since you didn't mention them that you don't have any experience with them.
They are an intriguing concept and apparently well executed.
You might go take a look at the Web address (above) for these antennas if
you want to learn more about them. I'm just a little suspicious of their
very, very good claims with short booms and small number of elements.
Best wishes and thanks again!
David (K5KH)
Fractenna
So dBi is nebulous; dBd is nebulous. Guess we should use dBG5RV from now
on.
;-)
Chip N1IR
William E. Sabin
Fractenna wrote:
>
> Thanks for the anatomy lesson on 'rear' vs 'back'..
>
> Can't seem to find this definition in any of my 40 antenna books though.
> Page? Year? Reference?
ARRL Antenna Book, 17th edition, chapter 11, especially Figs 5 thru 21.
See also Cushcraft data sheets for their monobanders. I am really
surprised that you haven't seen this before.
Bill W0IYH
MERVW2OE
The discussion of dBd, dBi, free space, real ground, front-to-back and
front-to-rear reminds me of a story my Dad (W4BVA) once told me. He
worked for Eastman Kodak and it seems they had just received a shipment of
a chemical they had ordered. The chemical came in a barrel with the
following instructions:
"This barrel should be opened from the bottom and not from the top.
Therefore the bottom has been marked 'top' and the top marked 'bottom' to
avoid confusion."
Nice to know there is no such confusion when we talk about antenna gain.
Regards, Merv
Fractenna
Like I said: try dBG5RV--no problems! :-)
Chip N1IR
Tom Rauch
On Wed, 14 May 1997 13:33:19 -0400, jc...@intrepid.net wrote:
>antenna? Seems to me that with real-world traps, there could also be
>current flow in parts of the trapped element that are not supposed to be
>active on a given band. And couldn't this result in cancellation of
>desired parts of the pattern? I don't know how to test this premise,
>but presumably folks on here can tell me if it's specious or not...
Just a opinion here. It makes sense that some unwanted current flows,
but I'd bet the value of unwanted current is small compared to a long
element tuned for the next band stuck in the middle of the array. If
unwanted currents don't kill antennas like the Sommers, I'd bet they
don't bother the trap antenna much either.
>Another question -- I saw a reference in this thread to work W1JR had
>done, showing typical losses of 1/2 dB per trap. What's the citation?
That would be good to know, because it is impossible to say they would
add "X" dB loss as a rule.
>The experiments K1KP did appeared not to show any such quantities (on a
>KT34XA's traps), but I'm not enough of an engineer to know if his tests
>were as good as they sounded, so I'd like to read what Joe has to say
>too.
Please, tell us what the K1KP experiment showed, and describe how he
did the test!!! This sounds like it could be the first REAL
measurement (I hope).
73 Tom
jc...@intrepid.net
Roy Lewallen wrote:
>
> In article <3375c6ec...@netnews.worldnet.att.net>,
> W8J...@worldnet.att.net (Tom Rauch) wrote:
> >. . .
> >I keep seeing "numbers" but I never find anyone who has supporting
> >data. If someone sends me a typical trap from any element of a common
> >trap antenna, I'll be glad to measure it on a Network Analyzer.
> >From that data, we could use EZnec to estimate the loss when the trap
> >is used in a real antenna. As I recall Tom Bruhn's measured a coaxial
> >cable trap, and it had a very good Q factor. Surely a lumped L/C
> >system could be even better.
> >
> >How could a carte blanche loss number be correct with so many
> >variables? Type of trap, trap location on the element, frequency,
> >which particular element, etc.etc. Current and impedance vary greatly,
> >so does trap construction. How could it possibly be quantified as "X"
> >dB loss per trap?
> >. . .
>
> I've done a little modeling of trapped antennas, but not with traps
> representing state-of-the-art for loss. They're traps I've made with RG-58.
> As I recall, effective inductor Q was around 200 (I can check). The
> interesting thing is that significant loss occurs only with certain
> combinations of bands. Typically, the traps will show low loss on all bands
> but one, and this is when certain combinations are used. For a three-band
> Field Day dipole, I use a two-band trap antenna with a dipole for a third
> band hung under it (but connected to the same feedpoint) as an inverted
> vee. I did this because the 3-band combination with traps I can easily make
> had too much loss on the third band. On the band where significant loss
> occurs, 2 dB is a typical value for the traps I construct.
>
> Tom's absolutely right that you can't assign a single loss value to traps.
> It depends not only on the trap construction, but the lengths of wire it's
> connected to (which determine the voltage across and current through it),
> and the frequency of operation.
>
> If you measure traps, Tom, make sure you simulate the potential
> shorted-turn effect of attached tubing.
>
> Roy Lewallen, W7EL
I just discovered this forum, and please be gentle if I'm traversing
previously-covered territory, but do trap losses and compromise spacing
have to be the only sources of diminished performance in a trapped
antenna? Seems to me that with real-world traps, there could also be
current flow in parts of the trapped element that are not supposed to be
active on a given band. And couldn't this result in cancellation of
desired parts of the pattern? I don't know how to test this premise,
but presumably folks on here can tell me if it's specious or not...
Another question -- I saw a reference in this thread to work W1JR had
done, showing typical losses of 1/2 dB per trap. What's the citation?
The experiments K1KP did appeared not to show any such quantities (on a
KT34XA's traps), but I'm not enough of an engineer to know if his tests
were as good as they sounded, so I'd like to read what Joe has to say
too.
Pete N4ZR
Peter Markham
It was said:
> Date: Tue, 13 May 97 18:11:48 PDT
> From: Ham-Ant Mailing List and Newsgroup <Ham...@ucsd.edu>
> Reply-to: Ham...@ucsd.edu
> Subject: Ham-Ant Digest V97 #444
> To: Ham...@ucsd.edu
> Date: 13 May 1997 15:37:51 GMT
> From: merv...@aol.com (MERVW2OE)
> Subject: Triband opinions
> ------------------------------
>
AO documentation gives the choice and a concise explaination:
3. Reference dB
To display gain figures in dBd rather than dBi, do the
following:
SET DB=dBd
To use dBd for free-space models and dBi over ground, do
this:
SET DB=dBdi
Gain in dBd is referenced to the peak gain of a halfwave
dipole in free space. Gain in dBi is referenced to an isotropic
radiator in free space. An isotropic antenna radiates equally
in all directions. A dipole has 2.15 dB gain over an isotropic
antenna, so AO converts from one gain reference to the other by
adding or subtracting 2.15 dB.
Pete/wa4hei
The meek will not inherit the Earth.
Jesse Touhey
On Wed, 14 May 1997 01:25:13 GMT, W8J...@worldnet.att.net (Tom Rauch)
wrote:
>Hi Roy and all,
>
>I wanted to get out of that Uni-hat yagi thread, and look at gain.
>
>I'm really puzzled by this:
>
>
>On Tue, 13 May 97 16:24:43 GMT, w7...@teleport.com (Roy Lewallen)
>wrote:
>
>>My feelings about dBd are elaborated in a section in the EZNEC and ELNEC
>>manuals titled "Why Not dBd?" Briefly, the problem with dBd is that people
>>tend to think it refers to the gain of a dipole over ground, which it
>>doesn't. It refers to the gain of a dipole in free space, which is just as
>>ficticious an antenna as an isotropic radiator.
>
>I have only two antenna engineering books with sections on gain
>measurements. They describe gain compared to some reference or
>standard antenna.
>
>They indicate the standard antenna is typically a dipole, and show
>test setups that substitute a dipole for the antenna under test and
>the reference antenna at the same location.
>
>None of them state the dipole is in freespace, since the descriptions
>are how to make proper measurements on a test range.
>
>Kraus shows this in Antennas on page 454. He clearly states gain of
>short wave arrays are measured "in reference to either a vertical or
>horizontal half wave antenna situated at a height equal to the average
>height of the array" . Kraus plainly indicates the properly
>constructed and matched half wave used is considered to be lossless,
>and the gain expressed is the power difference in dB measured in the
>center of the main lobe when one antenna is removed and the other
>substituted at the same mean height.
>
>Jasik does a similar thing on page 34-21 of his Antenna Engineering
>Handbook.
>
>When I delt with commercial communications antennas, they were always
>referenced to dipoles at the same mean array height. Because of the
>usage I am familiar with, I automatically assume if an antenna claims
>10 dBd gain, I assume an antenna is described having 10 dB gain over a
>properly matched well contructed dipole at the same height.
>
>I think only the models use dBi or dBd in freespace, since they can
>more accurately compare to such antennas. In the real world of real
>measurements, dBd or dBi freespace are useless quantities. No one can
>build or compare directly against a freespace antenna, although one
>can get an absolute power gain measurement from accurate measurement
>of field intensity and applied power.
>
>73, Tom
Hi Tom, yes! This is what I have been saying all along. "dbi" is a
mathematically derived hypothetical ratio reference to a "isotropic"
radiator. The isotropic radiator has no physical dimension and is a
free space reference ONLY. It is physically impossible to bring it in
earth's influence. "dBd" simply means a comparative ratio to a
dipole. Usually, that dipole has either replaced or is next to the
antenna under test. When a design model is taken off the drawing
board to do a real-world test, dBd comes into play. Yes, a dipole can
be modeled in free-space just like a Yagi can be modeled in
free-space.
In my experience "dBd" was used in the context just given way before
any antenna design software existed.
73, Jesse, W6KKT
.
Wes Stewart
*Hi Roy and all,
*
*I wanted to get out of that Uni-hat yagi thread, and look at gain.
*
*I'm really puzzled by this:
*
*
*On Tue, 13 May 97 16:24:43 GMT, w7...@teleport.com (Roy Lewallen)
*wrote:
*
*>My feelings about dBd are elaborated in a section in the EZNEC and
ELNEC
*>manuals titled "Why Not dBd?" Briefly, the problem with dBd is that
people
*>tend to think it refers to the gain of a dipole over ground, which
it
*>doesn't. It refers to the gain of a dipole in free space, which is
just as
*>ficticious an antenna as an isotropic radiator.
*
*I have only two antenna engineering books with sections on gain
*measurements. They describe gain compared to some reference or
*standard antenna.
*
*They indicate the standard antenna is typically a dipole, and show
*test setups that substitute a dipole for the antenna under test and
*the reference antenna at the same location.
*
*None of them state the dipole is in freespace, since the descriptions
*are how to make proper measurements on a test range.
*
*Kraus shows this in Antennas on page 454. He clearly states gain of
*short wave arrays are measured "in reference to either a vertical or
*horizontal half wave antenna situated at a height equal to the
average
*height of the array" . Kraus plainly indicates the properly
*constructed and matched half wave used is considered to be lossless,
*and the gain expressed is the power difference in dB measured in the
*center of the main lobe when one antenna is removed and the other
*substituted at the same mean height.
*
*Jasik does a similar thing on page 34-21 of his Antenna Engineering
*Handbook.
*
*When I delt with commercial communications antennas, they were always
*referenced to dipoles at the same mean array height. Because of the
*usage I am familiar with, I automatically assume if an antenna claims
*10 dBd gain, I assume an antenna is described having 10 dB gain over
a
*properly matched well contructed dipole at the same height.
*
*I think only the models use dBi or dBd in freespace, since they can
*more accurately compare to such antennas. In the real world of real
*measurements, dBd or dBi freespace are useless quantities. No one can
*build or compare directly against a freespace antenna, although one
*can get an absolute power gain measurement from accurate measurement
*of field intensity and applied power.
*
*73, Tom
Friends:
While I am certainly no antenna measurements expert, I have been
recently involved professionally with performing some microwave and
millimeter wave antenna measurements using a state-of-the-art compact
antenna range. From this perspective, I offer the following:
We hams tend to think of gain measurements in the context of a 20
meter dipole in the back yard.
As such, we think that free-space measurements are strictly
hypothetical, while in fact, there are hundreds, if not thousands of
anechoic chamber antenna ranges in the country. These chambers
simulate, with sufficient engineering accuracy, measurements in free
space. In addition, with modern network analyzers that offer time
domain gating, the effects of reflections in ground reflection ranges
can also be mitigated.
It is the reflections after all that make the difference between
"free-space" and "real-world" measurements. Eliminate the effects of
reflections on the measurements and free space performance can be
measured. When this is done, dBi is not necessarily an abstraction.
In simple English, the IEEE definition (1965) of power gain is the
ratio of power accepted by an antenna and radiated over a given area,
in a specified direction, to the power which would have been radiated
by a lossless isotropic antenna with the same input power. No dBd
here.
However, to compute (not measure) dBi, some other real antenna must be
used for comparison. By measuring two, or better, three "identical"
antennas, the gains of each of them individually may be determined.
After this is done, we can use one of them as a "standard gain"
antenna.
This standard is then measured in the same physical location as the
antenna to be tested and the range is "calibrated". The standard
antenna is then replaced by the test antenna and the relative gain is
determined.
The comparison antenna might be a dipole or more commonly at higher
frequencies a standard gain horn. Whatever, the gain of the standard
is normally backed out and the gain of the antenna under test is
specified in dBi.
This does not preclude however, the use of dBd if the reference was a
dipole. As Roy correctly points out in the EZNEC manual, the dipole
might not really have the theoretical 2.15 dBi gain under the strict
definition which includes power accepted as well as radiated by the
antenna. Even Kraus' assumption of a "lossless" half-wave reference
may be in error in the backyard case.
For a third reference book, I can recommend "Microwave Antenna
Measurements", published by Scientific-Atlanta.
Respectfully, Wes, N7WS
Jesse Touhey
On Thu, 15 May 1997 02:32:02 GMT, n7...@azstarnet.com (Wes Stewart)
wrote:
Hi Wes, thank you very much for the information. I didn't realize an
isotropic radiator could be duplicated.
Since this thread started about gain of HF Tri-band Yagis. What is
your recommendation as to how to conduct cost effective, specification
performance tests, on the beasts.
Respectfully, Jesse, W6KKT
Tom Rauch
>As such, we think that free-space measurements are strictly
>hypothetical, while in fact, there are hundreds, if not thousands of
>anechoic chamber antenna ranges in the country. These chambers
>simulate, with sufficient engineering accuracy, measurements in free
>space. In addition, with modern network analyzers that offer time
>domain gating, the effects of reflections in ground reflection ranges
>can also be mitigated.
Hi Wes,
That's a nice explaination, but I think this is one of those
subjective threads that has no single correct answer. It is a
perspective problem, since there are no written rules. There are,
however correct ways of measuring things as well as incorrect ways
that "sound good".
Perhaps the perspective comes more from the frequency range we are
used to, than the fact we are Hams. I tend to think in terms of what
commercial people do at HF and MW, rather than VHF and higher.
Especially when someone publishes gain for a tri-band yagi. I know
Jesse, with his experience, thinks the same way as do several others
(I have spoken with) who mainly work with lower frequency antennas.
It's pretty tough to find an anechoic chamber large enough to measure
a multi-element HF array. It's also unlikely to find a ground screen
covered range for lower frequencies. It seems almost silly and is
almost certainly inaccurate to use dBi or dBd (freespace) when talking
about measurements on a HF array, since there is little likelihood the
"tester" would have any idea of the exact ground characteristics that
greatly influence the antenna's absolute radiated power.
Of course by installing and measuring a conventional simple reference
antenna at the same mean height with the same polarity as the unknown
antenna, a freespace value could be obtained. The ground would affect
the dipole or array about the same if the mean height were the same.
In that case dBd could mean EITHER freespace or against ground, there
would be little difference since the initial measurement was against a
reference at the same mean height over the same earth. In any case the
efficioency of the dipole would matter little (as long as it was well
built) since other losses would skew the results more.
While I do find texts that totally agree with you, most HF stuff I
find is referenced to a dipole at the same mean height as the array
being tested.
Not of this would be an issue IF the manufacturer pointed out how the
measurement was taken. For example Lew keeps repeating figures from a
test taken many years ago, where the antenna was compared to a dipole.
The measurements were taken at one height, and we have no idea if we
were in the main lobe or moving towards the nulls of the antennas.
From the test description it was pretty clear they were not even close
to the elevation pattern lobe center, so the measurements mean almost
nothing.
My point is NONE of these measurements mean anything in the end
application. The only meaningful method would be to do something like
Kraus and others suggest, measure the CENTER of the main lobe or the
signal at the desired angle. For VHF and higher, freespace is fine. I
don't think we can assume anything is standard, just more typical for
that frequency range.
I hope my thinking was not too "fuzzy" (as Cecil says) to follow.
73, Tom
Fractenna
Hi Wes--
Thanks fer corroboration.
73
Chip N1IR
William E. Sabin
Wes Stewart wrote:
>
>
> This does not preclude however, the use of dBd if the reference was a
> dipole. As Roy correctly points out in the EZNEC manual, the dipole
> might not really have the theoretical 2.15 dBi gain under the strict
> definition which includes power accepted as well as radiated by the
> antenna. Even Kraus' assumption of a "lossless" half-wave reference
> may be in error in the backyard case.
>
The efficiency of the real-world dipole is measurable and can be
corrected for to get the radiation from a lossless dipole.
This efficiency can be measured by integrating the far field power
density over a spherical surface and comparing that with the dipole's
input power. Is that what the anechoic chamber guys do?
Bill W0IYH
William E. Sabin
Tom Rauch wrote:
>
>
> Hi Wes,
>
> That's a nice explaination,
Yes, a very nice explanation, and very interesting.
Bill W0IYH
Rick Craig, N6ND
There are some pitfalls that must be avoided when trying to measure
the
gain of a yagi by the dipole substitution method over ground. IF you
have good ground, a dipole will have close to 6 dB of ground
reflection
gain at almost any height. A yagi, and in particular long boom high
gain
yagis, need to be fairly high ( 1 to 2 wavelengths minimum) before
they
approach 6 dB of ground reflection gain. If your "test range" only
allows
you to mount antennas 1/2 wave high, the measured gain of the yagi
could be
low by as much as 2 dB. Also the main lob of a long boom yagi will be
at a
slightly lower angle than the main lob of a dipole at the same height.
dBd
is certainly a valid measurement if referenced to a dipole at the same
height, but it must be done carefully.
73 Rick, N6ND
cra...@nosc.mil
w6...@frazmtn.com (Jesse Touhey) wrote:
>On Tue, 13 May 97 16:24:43 GMT, w7...@teleport.com (Roy Lewallen)
>wrote:
>>My feelings about dBd are elaborated in a section in the EZNEC and ELNEC
>>manuals titled "Why Not dBd?" Briefly, the problem with dBd is that people
>>tend to think it refers to the gain of a dipole over ground, which it
>>doeound, a dipole will have close to 6 dB of ground reflection
gain at almost any height. A yagi, and in particular long boom high
gain
yagis, need to be fairly high ( 1 to 2 wavelengths minimum) before
they
approach 6 dB of ground reflection gain. If your "test range" only
allows
you to mount antennas 1/2 wave high, the measured gain of the yagi
could be
low by as much as 2 dB. Also the main lob of a long boom yagi will be
at a
slightly lower angle than the main lob of a dipole at the same height.
Jesse Touhey
Snip
>
>Friends:
>
>While I am certainly no antenna measurements expert, I have been
>recently involved professionally with performing some microwave and
>millimeter wave antenna measurements using a state-of-the-art compact
>antenna range. From this perspective, I offer the following:
>
>We hams tend to think of gain measurements in the context of a 20
>meter dipole in the back yard.
>
>hypothetical, while in fact, there are hundreds, if not thousands of
>anechoic chamber antenna ranges in the country. These chambers
>simulate, with sufficient engineering accuracy, measurements in free
>space. In addition, with modern network analyzers that offer time
>domain gating, the effects of reflections in ground reflection ranges
>can also be mitigated.
>
>"free-space" and "real-world" measurements. Eliminate the effects of
>reflections on the measurements and free space performance can be
>measured. When this is done, dBi is not necessarily an abstraction.
>
>In simple English, the IEEE definition (1965) of power gain is the
>ratio of power accepted by an antenna and radiated over a given area,
>in a specified direction, to the power which would have been radiated
>by a lossless isotropic antenna with the same input power. No dBd
>here.
>
>However, to compute (not measure) dBi, some other real antenna must be
>used for comparison. By measuring two, or better, three "identical"
>antennas, the gains of each of them individually may be determined.
>After this is done, we can use one of them as a "standard gain"
>antenna.
>
>This standard is then measured in the same physical location as the
>antenna to be tested and the range is "calibrated". The standard
>antenna is then replaced by the test antenna and the relative gain is
>determined.
>
>The comparison antenna might be a dipole or more commonly at higher
>frequencies a standard gain horn. Whatever, the gain of the standard
>is normally backed out and the gain of the antenna under test is
>specified in dBi.
compared with the replacement dipole (dBd)??
>
>This does not preclude however, the use of dBd if the reference was a
>dipole.
Wes, what is ment by the above sentence? What is the common
interpretation for the statement "dBd"?
Respectfully, Jesse, W6KKT
Snip, Snip
Hi Wes, again, thanks for informative gain measurement techniques.
MERVW2OE
In article <337bad3...@news.azstarnet.com>, n7...@azstarnet.com (Wes
Stewart) writes:
>but we still can't make (as far as I know) an antenna that radiates
>uniformly in every direction.
Actually, Brian Beezley provides a 146 MHz model with AO which comes
awfully close. It is composed of 8 wires, with 4 sources 2 of which are
90 degrees out of phase with the other two. I found it more than slightly
amusing that AO calculates the gain of this antenna as: -2.05 dBd.
Regards, Merv
Wes Stewart
On Thu, 15 May 1997 08:23:14 -0600, "William E. Sabin"
<sab...@crpl.cedar-rapids.lib.ia.us> wrote:
*Wes Stewart wrote:
*>
*>
*> This does not preclude however, the use of dBd if the reference was
a
*> dipole. As Roy correctly points out in the EZNEC manual, the dipole
*> might not really have the theoretical 2.15 dBi gain under the
strict
*> definition which includes power accepted as well as radiated by the
*> antenna. Even Kraus' assumption of a "lossless" half-wave
reference
*> may be in error in the backyard case.
*>
*
*The efficiency of the real-world dipole is measurable and can be
*corrected for to get the radiation from a lossless dipole.
*
*This efficiency can be measured by integrating the far field power
*density over a spherical surface and comparing that with the dipole's
*input power. Is that what the anechoic chamber guys do?
*
*Bill W0IYH
Bill,
I am really somewhat of a novice at this and can't speak for others,
but that's not what we do.
Of course, we are working on missile seeker antennas and are often
more concerned with pattern measurements than absolute gain. We
usually assume some aperature efficiency and then if the patterns work
out, we're happy.
In a nutshell though, to calibrate a standard antenna, we would use
two "identical" antennas a known distance apart. We put in some power
to one of them and measure what comes out the other one. Assuming the
antennas are far enough apart that the wave illuminating the receive
antenna approximates a plane wave, and knowing the range and
wavelength, the "gains" of the two antennas can be computed.
In the case where the two antennas aren't identical, a third can be
introduced and all three measured in all possible combinations and by
solving three simultaneous equations, the gain of each individual can
be determined.
Typically, the source and power meter consist of an automatic network
analyzer that can be used for swept frequency measurements and can be
calibrated to remove cable losses, mismatch effects, etc.
In the compact range that I spoke of, the range is actually folded and
two specially shaped mirrors are used bounce the signal from one
antenna to the next and to "flatten" the phase front at the location
of the test antenna. This allows reasonable accuracy down to about 1
GHz in an enclosure of only 25' X 25' X 50'. An "unfolded" range would
have to be many times this length for similar performance.
For pattern measurements, a motorized, computer controlled positioner
allows for limited elevation and unlimited azimuth and roll
(polarization) movements. (I could use this on my EME array although
I don't need 0.01 degree accuracy) Although the tower on the
positioner is fiberglass, the gearhead for roll positioning is metal,
so complete azimuth patterns (FB) are tough. For our applications
though we usually have a missile behind the antenna anyway :)
73, Wes N7WS
Jari Jokiniemi
In article <5lf89u$7...@poisson.nosc.mil> cra...@nosc.mil (Rick Craig, N6ND) writes:
gain at almost any height. A yagi, and in particular long boom high gain
yagis, need to be fairly high ( 1 to 2 wavelengths minimum) before
That means that to measure a typical triband trap yagi you only need a
tower of some 20 to 40 meters of height which are standard towers of
any serious DXer.
--
Jari Jokiniemi, jari.jo...@tekla.fi, OH3BU, OH2MPO
Tekla Oy, Koronakatu 1, 02210 Espoo, +358-9-8879 474
Tom Rauch
On Fri, 16 May 1997 01:03:53 GMT, n7...@azstarnet.com (Wes Stewart)
wrote:
>I plead guilty to getting far afield (no pun intended) from the
>original triband thread, but somebody else renamed it didn't they:)
>
>As to the original problem, I'm as mystified as the next guy. The
>reference I cited, describes methods of measurement over ground,
>however, the required separation between antennas and the required
>heights above ground (>4 wavelengths) would be a real problem at 20
>meters.
Hi Wes,
I suspect the problem is that everyone is too vague in their
descriptions, so we all operate on assumptions.
All complex non-standardized measurements need to be carefully
reviewed for proper methods.
With HF arrays, the normal trend (as far as I know and can find) was
to reference them to a dipole at the same mean height, and make the
measurement at the pattern elevation peak. While that may not be
perfect, it is a far cry from ignoring ground losses or using a
unverified model.
VHF and higher is a different ball game.
73 Tom
Jesse Touhey
On Fri, 16 May 1997 02:40:44 GMT, n7...@azstarnet.com (Wes Stewart)
wrote:
>On Thu, 15 May 1997 21:12:07 GMT, w6...@frazmtn.com (Jesse Touhey)
>wrote:
>
>*On Thu, 15 May 1997 02:32:02 GMT, n7...@azstarnet.com (Wes Stewart)
>*wrote:
>*Snip
>*Snip
>*>
>{more snipping}
>
>*>This standard is then measured in the same physical location as the
>*>antenna to be tested and the range is "calibrated". The standard
>*>antenna is then replaced by the test antenna and the relative gain
>is
>*>determined.
>*>
>*>The comparison antenna might be a dipole or more commonly at higher
>*>frequencies a standard gain horn. Whatever, the gain of the standard
>*>is normally backed out and the gain of the antenna under test is
>*>specified in dBi.
>*HF horiz gain figures in dBi will always look much better than
>*compared with the replacement dipole (dBd)??
>*
>*>
>*>This does not preclude however, the use of dBd if the reference was
>a
>*>dipole.
>*Wes, what is ment by the above sentence? What is the common
>*interpretation for the statement "dBd"?
>*Respectfully, Jesse, W6KKT
>
>Jesse, I think the common interpretation is that:
>
>1) the gain of the test antenna is measured in the direction of
>maximum radiation intensity and
>
>2) gain with respect to a dipole (dBd) is the ratio of this number to
>that of a well constructed dipole located in the same physical
>location and aligned so its maximum radiation intensity is in the same
>direction as the comparison antenna as stated above.
I agree 100% with the above. And, it is not "written in blood" one
need to interpolate the dBd plots into dBi. My point: For HF gain
measurements, the term "dBd" is a commonly used term to denote
HF gain comparative measurements to a well constructed dipole over
real ground. It has nothing to do with "free space" unless so
specified.
>3) if the test antenna located over ground has maximum radiation
>intensity at 20 degrees elevation, then the dipole radiation should be
>measured at 20 degrees.
One should conduct gain/elev plots for a compete analysis. However,
HF common practice is to compare the test antenna to the maximum
radiation intensity of the "standard" at the same mean height above
the same medium.
>
>Now, I'm NOT claiming expertise, I'm just reporting what *I think* is
>generally accepted. Obviously, because we're having this discussion,
>there isn't total agreement.:D
>
>*Snip, Snip
>*
>*Hi Wes, again, thanks for informative gain measurement techniques.
>*
>
>You're welcome.
>
>73, Wes N7WS
Hi Wes, I personally use the isotropic as my "standard" for gain
comparisons when using Eznec. As I said before, I took issue only
with Roy's interpretation concerning dBd. He said, it pertained to a
dipole in free-space. I say not necessarily so.
Again, thanks for your input. I always enjoy and learn much from your
threads.
Respectfully, Jesse, W6KKT
Ian White, G3SEK
Jari Jokiniemi wrote:
>
>In article <5lf89u$7...@poisson.nosc.mil> cra...@nosc.mil (Rick Craig, N6ND)
>writes:
> gain at almost any height. A yagi, and in particular long boom high gain
> yagis, need to be fairly high ( 1 to 2 wavelengths minimum) before
>
>That means that to measure a typical triband trap yagi you only need a
>tower of some 20 to 40 meters of height which are standard towers of
>any serious DXer.
That, and a helicopter with precision flying equipment to find and
measure the main lobe.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
William E. Sabin
Wes Stewart wrote:
>
>
> *>This standard is then measured in the same physical location as the
> *>antenna to be tested and the range is "calibrated". The standard
> *>antenna is then replaced by the test antenna and the relative gain
> is
> *>determined.
The losses of the reference dipole (but not its ground *reflection*
losses) should be calibrated out so that we are comparing a real-world
beam with a lossless dipole. Also, the ground reflection angles should
be the same, or if they are not that should be taken into account (this
could be messy).
Bill W0IYH
Jim Garver
In article <19970516025...@ladder02.news.aol.com>,
That is a wierd antenna, eh? I wonder if anyone has ever made one.
In any case, an antenna like this, as well as some of the arguments
in this thread, belong in outer space where there are no ground
reflections. Now wouldn't that make a nice antenna range?
I tried modeling antennas 150 miles high using MN, AO's earlier version.
I finally figured out that I can never get an antenna high enough to
escape ground reflections in a simulation where the world is flat!
K7YO
--
jga...@ichips.intel.com K7YO I don't speak for Intel
Wes Stewart
*On Thu, 15 May 1997 02:32:02 GMT, n7...@azstarnet.com (Wes Stewart)
*wrote:
*Snip
*Snip
*>
{more snipping}
*>This standard is then measured in the same physical location as the
*>antenna to be tested and the range is "calibrated". The standard
*>antenna is then replaced by the test antenna and the relative gain
is
*>determined.
*>
*>The comparison antenna might be a dipole or more commonly at higher
*>frequencies a standard gain horn. Whatever, the gain of the standard
*>is normally backed out and the gain of the antenna under test is
*>specified in dBi.
*HF horiz gain figures in dBi will always look much better than
*compared with the replacement dipole (dBd)??
*
*>
*>This does not preclude however, the use of dBd if the reference was
a
*>dipole.
*Wes, what is ment by the above sentence? What is the common
*interpretation for the statement "dBd"?
*Respectfully, Jesse, W6KKT
Jesse, I think the common interpretation is that:
1) the gain of the test antenna is measured in the direction of
maximum radiation intensity and
2) gain with respect to a dipole (dBd) is the ratio of this number to
that of a well constructed dipole located in the same physical
location and aligned so its maximum radiation intensity is in the same
direction as the comparison antenna as stated above.
3) if the test antenna located over ground has maximum radiation
intensity at 20 degrees elevation, then the dipole radiation should be
measured at 20 degrees.
Now, I'm NOT claiming expertise, I'm just reporting what *I think* is
Fractenna
RE: FRONT and BACK anatomy
My point is that the definition is rather arbitrary and not defined in the
'pro' books, Bill. You seemed to have affirmed that. As for sidelobes, I
think I've had quite a bit of education on them given a background in
radio astronomy.
73
Chip N1IR
Bart Rowlett
In article <337bb2d8...@news.azstarnet.com>,
Wes Stewart <n7...@azstarnet.com> wrote:
>On Thu, 15 May 1997 08:23:14 -0600, "William E. Sabin"
><sab...@crpl.cedar-rapids.lib.ia.us> wrote:
>
>*Wes Stewart wrote:
[dBd stuff deleted]
The approach used by my employer to determine the far field pattern of
large, high gain spacecraft antennas is to mount the antenna system (usually
attached to the vehicle) inside the chamber and excite it with a signal source.
Located a few feet from the antenna is a very large XY stage which is able to
move a small horn sample antenna anywhere in a plane which extends well beyond
the antenna aperture and is approximately perpendicular to the beam. The
amplitude and phase (compared to the reference) are sampled on grid points
roughly a quarter wavelength apart in X and Y. The data collection process
can take many hours. Once the data is collected it is corrected for known
mechanical and electrical effects and then processed to determine the far
field pattern from the array of near field samples. The transformation is
done by computing the discrete fourier transform (2 dimensions) of the near
field data vector which results in the far field pattern but still may require
some 'unwarping' depending on the beamwidth on so forth. Last I was involved,
the overall accuracy at computing patterns was satisfactory but the absolute
gain calibration wasn't good enough to get a reliable estimate of antenna
system efficiency. That was done by a direct measurement in the main lobe.
bart wb6hqk
Jesse Touhey
Hi Chip, many of your posts seem like private email, and are difficult
to understand what you are talking about. Why not try including some
of the original thread you are addressing? :>)
73, Jesse, W6KKT