DDRR--Results?
Fractenna
Hi All--
Tom W8JI recently posted a comment to the effect of: "the DDRR...a few
people that swear they work...might even invent cases where the (SIC)
claim results..."
Not sure about this 'invent..results' stuff.. or what Tom means by this.
What REAL results do you have?
Anyone work with these antennae? I have been working with some microwave
versions for the last 2 months and quite happy with the results. What have
you found? My impression is that this is one of the most misunderstood of
antennae--and among the least used. Let me know what you've found and I'll
put some more of my results up on the newsgroup.
One important note: the EFFICIENCY of the DDRR family is strongly
dependent on the ground screen used and the HEIGHT of the ring. My results
are with a 5% of a wave (or greater ) height. Also note: ARRL pubs (in my
opinion) do a poor job (let me be more specific--an incomplete job) of
describing the variations of DDRR's--so beware.
Also note: I am (personally) not interested in a comparison to another
antenna type; just what you've found for the DDRR.
73
Chip N1IR
Madjid
Hi Chip,
I posted some messages on the DDRR some time ago. Tom (W8JI) said
that it is a very inefficient radiator .... but I think that we
were not talking about the same thing.
We have a bunch of guys testing DDRRs in VE2 land and they work.
The originator of all that is Tony, VE2DLJ, who has been in contact
with Dr. Boyer, the guy responsible for the DDRR project at Loockhed.
Tony doesn't have access to internet but I can tell you that:
1. The "DDRR" described in ARRL antenna handbook IS NOT, I repeat
IS NOT, a real DDRR. It is designed contrary to all recommendations
made by Dr Boyer (Exhaust pipe, short vertical post and chicken wire
as
ground). Boyer was horrified when he saw that "chicken wire DDRR",
so let's forget about that contraption, it is a poor antenna.
2. There are two types of DDRRs the One ring and the two rings.
The one ring need a SOLID GROUND below. Boyer and his team made
some measurements and found that radials, grid wire etc DO NOT
work because return currents in the near field are not really
radial. If you go to my home page in the picture section you
will see an old picture of BOYER's DDRRs and the 1/2 square mile
SOLID COPPER GROUND. In that configuration the DDRR is a vertical
short monopole.
To solve the problem of solid ground, Boyer designed a TWO ring DDRR.
In that configuration the top and bottom ring act as a gigantic open
line transmission line between the source and capacitor. As with open
lines, losses are minimal and interaction with the environment reduced.
Even at 3 feet above ground for the 80m DDRR, there is however an
interaction with the ground by capacitive coupling. For one KW the
RF current in the vertical post is in the 50 Amp range and this is
one of the reasons for the "efficiency". The Near Field is almost
entierely magnetic and Magnetic losses in the ground are negligible
(see Ground losses below). Radiation resistance (Calculated) is .9 ohms
so any small defect in contacts, reduced size of pipes, use of iron
instead of Aluminium or copper will deteriorate the performance of
the antenna very rapidly.
Horizontal sections do not contribute to the Far field and you get
a very low angle (20-26 TOA) BUT DX performance is still related
to Brewster angle. If you got bad ground around your QTH forget it!
We have in VE2, four or five guys who build different types of
2 ring DDRRs (20m wire, 20m 1/4" cop.tube, 80m wire, heliax and
4" Aluminium tubing by VE2DLJ). Preliminary tests with the 20m DDRR
(wire and 1/4" cop. tube) showed surprisingly that performance was
equivalent to a three element beam for Europe. I find that a little
bit too much, but the two guys who made the measurements have both
PhDs in Physics and were not drunk at the time so I have to accept
that. They made multiple contacts and A/B tests from the same QTH.
Tony, VE2DLJ, has build two full size DDRRs for 80m and is actually
in the process of phasing them to eliminate the omnidirectional
problem. He can be heard in the 75m DX window almost every day
working long haul DX like VK/ZL with good results.
To those who are skeptics about the tests and methodology, I will
add that most people conducting these tests have PhDs and used
to the scientific method. They have reference antennas spaced far
enough to make A/B tests. Most of them keep logs of their measurements
and contacts. At least two of them have top notch tranceivers very well
calibrated. On top of that a group of silent "monitoring stations", like
me, listen to the QSOs to compare our own reports on the DX to theirs.
Is the DDRR a magical antenna ? NO ! VE2HQ with his beam at 130 feet
has consistently beaten Tony with his DDRRs. Reception on the DDRRs is
however superior even with the omni pattern. Compilation of results will
be done next spring and posted in my page (Pictures & Antenna shootout).
Boyer published an excellent article (2 parts) in 73 Magazine with
all calculations (Transmission line based) to design your own DDRRs.
Tom made some comments once on the fact that Hams are generally
dazzled by maths sprinkled in articles to impress the naive reader,
but I am not easy to "dazzle". I had Maxwell, Shroedinger, Bra and
Kets <|> for breakfast and diner for years, long time ago, and
the maths in Boyer's articles are accessible to most Hams anyway.
I don't have a year/date for the articles. The only thing I know
is that it was published in 73 under the title "Surprising miniature
Low Band antenna" in two parts, by Boyer.
===================================================================
About GROUND losses:
There was much debate lately about magnetic losses in the ground vs
electric losses. Due to newsgroup reader and editor limitations I
can't write the whole demonstration. It is arduous and complicated,
so you have accept or search in scientific publications or books on
Electrodynamics for proof/confirmation.
Losses in the ground are only related to the IMAGINARY part of the
dielectric and permeability of a medium and can be calculated
(derived from Maxwell microscopic equations after much fiddling) as:
Q = Omega/4Pi(imag(Epsilon) Eav^2 + imag(Mu). Hav^2)
Q is heat loss by unit volume (cm^3 here)
Eav, Hav is average in time of E and H (Bar on top)
A study of Epsilon and Mu and the dispertion Epsilon(omega) and
Mu(omega) [H.Kramers & R.Koenig 1927] show that:
a. Epsilon imaginary part is very important. In fact the development of
Epsilon(w) begins by j.4.Pi.sigma/w and for dielectrics and bad
conductors and heterogeneous dielectrics the two first terms:
epsilon(w) = epsilon0 + j.4.Pi.sigma/w
The Kramers-Koenig complex integrals are used to calculate real
or imaginary part of Epsilon. I don't have NEC2 documentation
but SOMNEC code uses - j.2.Pi.sigma.(59.96)/w as imaginary part
which could be an estimate of the integrals (seems high though).
The minus sign seems to come from internal NEC2 representation
of exp(j.w.t) by exp(-j.w.t)...
b. Mu imaginary part is small and negligible in dielectrics. Countrary
to Epsilon, Mu looses rapidly its physical meaning when frequency
increases and equal to 1 even when well below optical frequencies
(transparency domain). Imag(Mu) becomes ZERO .. and magnetic
losses are nil.
It is true that magnetic losses are never zero in equation above,
but they are so small compared to dieletric losses that I will
just forget about them when dealing with the ground or any
dielectric at HF or above. Metallic/magnetic/plasma mediums are
a totally different story...
[Theoretical study of EM losses found in Landau and Lifchitz,
Quantum Electrodynamics/Electrodymanics of continuous mediums, 1969]
Madjid
-------------------
Madjid, VE2GMI - Home Page: http://www.CAM.ORG/~mboukri
NEC4WIN Antenna simulation for Windows
frac...@aol.com
RE: Madjid's results
I find this fascinating! Have you tried a PIFA type of feed? What about
the 1 wave rings? NEAT STUFF! See my latest ' RE: DDRR' posting.
I agree; the ARRL 'tailpipe special' isn't the best DDRR, but as you have
said, there are others!
Thanks for having the intestinal fortitude to come on the newsgroup; we
need people to share their comments, not feel that they're using the
'wrong' antenna based on someone' else's opinion on what a 'better' on is!
73
Chip N1IR
w8j...@aol.com
Hi Madjid,
In article <327EBD...@cam.org>, Madjid <mbo...@cam.org> writes:
>I posted some messages on the DDRR some time ago. Tom (W8JI) said
>that it is a very inefficient radiator .... but I think that we
>were not talking about the same thing.
>The one ring need a SOLID GROUND below. Boyer and his team made
>some measurements and found that radials, grid wire etc DO NOT
>work because return currents in the near field are not really
>radial. If you go to my home page in the picture section you
>will see an old picture of BOYER's DDRRs and the 1/2 square mile
>SOLID COPPER GROUND. In that configuration the DDRR is a vertical
>short monopole.
Then we agree Madjid. But few Hams have a 1/2 square mile copper ground,
and even if they did a short vertical with a hat would radiate just as
effectively.
>To solve the problem of solid ground, Boyer designed a TWO ring DDRR.
>In that configuration the top and bottom ring act as a gigantic open
>line transmission line between the source and capacitor. As with open
>lines, losses are minimal and interaction with the environment reduced.
Losses will increase by a factor of two when compared to the perfect
groundplane case. But that may be better than a poor groundplane. In any
event, if DDRR rings are replaced with disks the radiation efficiency
remains the same. So the antenna is understandable in this configuration.
Hams should NOT confuse it with an antenna made out of a small more
resistive element like wire or pipe with junctions, nor should they use a
lossy conventional air type capacitor.
>Even at 3 feet above ground for the 80m DDRR, there is however an
>interaction with the ground by capacitive coupling. For one KW the
>RF current in the vertical post is in the 50 Amp range and this is
>one of the reasons for the "efficiency". The Near Field is almost
>entierely magnetic and Magnetic losses in the ground are negligible
>(see Ground losses below). Radiation resistance (Calculated) is .9 ohms
>so any small defect in contacts, reduced size of pipes, use of iron
>instead of Aluminium or copper will deteriorate the performance of
>the antenna very rapidly.
We will have to agree to disagree about ground losses, since FS
measurements seem to be in dispute with that Madjid.
>Horizontal sections do not contribute to the Far field and you get
>a very low angle (20-26 TOA) BUT DX performance is still related
>to Brewster angle. If you got bad ground around your QTH forget it!
Hence radiation field losses are important. Also Madjid, the time varying
magnetic induction field is always accompanied by a time varying electric
field. perhaps you saw the thread with Roy Lewallen and the rest?
>We have in VE2, four or five guys who build different types of
>2 ring DDRRs (20m wire, 20m 1/4" cop.tube, 80m wire, heliax and
>4" Aluminium tubing by VE2DLJ). Preliminary tests with the 20m DDRR
>(wire and 1/4" cop. tube) showed surprisingly that performance was
>equivalent to a three element beam for Europe. I find that a little
>bit too much, but the two guys who made the measurements have both
>PhDs in Physics and were not drunk at the time so I have to accept
>that. They made multiple contacts and A/B tests from the same QTH.
I find that impossible to believe, unless the tribander was very poor.
Even if the DDRR antenna was 100% efficient, it has less directivity than
a dipole. Witout directivity, it can have no gain.
>Is the DDRR a magical antenna ? NO ! VE2HQ with his beam at 130 feet
>has consistently beaten Tony with his DDRRs. Reception on the DDRRs is
>however superior even with the omni pattern. Compilation of results will
>be done next spring and posted in my page (Pictures & Antenna shootout).
On what band? If it is on HF then location can have much more to do with
it than antenna gain.
We seem to agree on most of this Madjid, except the groud loss issue.
Antenna's work the way they work, and none of it is magic. The only area
lacking in scientific data surrounds induction field effects in soil.
From your original post, I gathered the claim was made a DDRR would beat
larger full size antennas. of course, that is a claim we both have
problems with, as you pointed out.
I can work VK longpath from my mobile with a conventional hat loaded
vertical on 75, and I have worked VK shortpath on 160 also. That antenna
is 1% efficient on 160 (measured and calculated data), and perhaps 15% on
75 (calculated). We have to be careful using over the air data.
73 Tom
Jake Brodsky
w8j...@aol.com wrote:
>
<lots of other interesting stuff snipped>
> Losses will increase by a factor of two when compared to the perfect
> groundplane case. But that may be better than a poor groundplane. In any
> event, if DDRR rings are replaced with disks the radiation efficiency
> remains the same.
<still more interesting stuff snipped>
This seems to be the key issue here Tom. How do you evaluate
radiation efficiency, and why should disks be a similar
substitute?
73,
Jake Brodsky, mailto:fru...@erols.com
PP-ASEL IA, Cessna Cardinal N30946, Based @ MD24
Amateur Radio Station AB3A
"Beware of the massive impossible!"
at...@imap1.asu.edu
Madjid (mbo...@cam.org) wrote:
: We have in VE2, four or five guys who build different types of
: 2 ring DDRRs (20m wire, 20m 1/4" cop.tube, 80m wire, heliax and
: 4" Aluminium tubing by VE2DLJ). Preliminary tests with the 20m DDRR
: (wire and 1/4" cop. tube) showed surprisingly that performance was
: equivalent to a three element beam for Europe. I find that a little
: bit too much, but the two guys who made the measurements have both
: PhDs in Physics and were not drunk at the time so I have to accept
: that. They made multiple contacts and A/B tests from the same QTH.
You shouldn't accept this because they have Ph.D.s in physics. One key
word here is preliminary. When people give talks at conferences and
say their "preliminary results are ..." they are telling you that they
haven't checked their work carefully.
Actually, I find it amazing that someone with a Ph.D. in physics would
spend their time playing around with DDRRs. You have to accept that
because I too have a Ph.D. in physics :-).
73 Kevin w9...@ptolemy.la.asu.edu
Robert Casey
I have a DDRR antenna in the attic tucked under the roof next to the
chimney ("dead" space between chimney and gutter under roof), and
it seems to work pretty well. It's a manufactured magmount intended
for mobile service. it's sitting on a 19' rackmount steel panet that
is normally about 18 inches tall. Oh, yea, it's for 2 meters.
I don't remember who made this antenna.
w8j...@aol.com
In article <32877A...@erols.com>, Jake Brodsky <fru...@erols.com>
writes:
>This seems to be the key issue here Tom. How do you evaluate
>radiation efficiency,
There are simple ways of evaluating things that reduce errors and provide
more conclusive data. When someone has time to do all sorts of low
accuracy tests and write several articles, surely he has time to do a
meaningful test and answer a few questions about the methods he used.
A good way is to install a simple well known reference antenna in a clear
area, and do FS measurements of some form. It isn't all that complicated.
> and why should disks be a similar
>substitute?
All the "non-radiating"(hopefully) transmission line at the top does is
load the antenna. The goal is to provide a low impedance load for the
section of the antenna that radiates, so current can be made to flow
uniformly throughout the entire radiating area.
If a large hat is used, current quickly disperses in the hat and I^2 R
losses decrease. That's why a large hat is the most efficient way to load
a radiator. Since current (charges) move uniformly away from the antennas
connection point at the center, radiation from the hat cancels. That
decreases radiation losses. The hat thus offers a very low loss loading
impedance, allowing large amounts of current to flow unopposed in the
short radiator.
Any move away from this decreases efficiency. A folded over top loading
conductor (like the DDRR) is a slight move away from ideal, and the
greatest move would be base loading. There are many things in between. I
see no reason to get excited about wild claims poorer loading schemes are
something special. I don't consider a very short top loaded vertical to be
an "efficient radiator", do you?
When I hear the claim a specially constructed DDRR over a 1/2 mile copper
ground screen one works well, it's easy to understand. I'll buy that. It's
the next thing down the line from ideal for a given height.
When I hear a claim saying a DDRR beat or tied a near full-size beam,
that's just plain silly. Perhaps the beam was pointed the wrong way.
73 Tom
Madjid
w8j...@aol.com wrote:
> Then we agree Madjid. But few Hams have a 1/2 square mile copper ground,
> and even if they did a short vertical with a hat would radiate just as
> effectively.
Disagree, a short thick vertical with a hat or two hats center fed will
almost certainly radiate effectively. But the field around that type
of antenna is Highly "Electric" and losses in the ground will be higher.
Remember? Losses are mainly Dielectric (I think we desagree on that
too!).
> Losses will increase by a factor of two when compared to the perfect
> groundplane case. But that may be better than a poor groundplane. In any
> event, if DDRR rings are replaced with disks the radiation efficiency
> remains the same. So the antenna is understandable in this configuration.
I am not following you on that factor 2. ..--..
> Hams should NOT confuse it with an antenna made out of a small more
> resistive element like wire or pipe with junctions, nor should they use a
> lossy conventional air type capacitor.
Exactly. That's why I will never build a DDRR. The price performance
ratio is too high. After all the max it could do is to be a "perfect"
1/4 wave vertical.
> We will have to agree to disagree about ground losses, since FS
> measurements seem to be in dispute with that Madjid.
> Hence radiation field losses are important. Also Madjid, the time varying
> magnetic induction field is always accompanied by a time varying electric
> field. perhaps you saw the thread with Roy Lewallen and the rest?
Agreed to disagree. I didn't do FS measurements myself and can't
comment on that. I will be curious to know who made them.
>>....
> >equivalent to a three element beam for Europe. I find that a little
> >bit too much, but the two guys who made the measurements have both
> >PhDs in Physics and were not drunk at the time so I have to accept
> >that. They made multiple contacts and A/B tests from the same QTH.
>
> I find that impossible to believe, unless the tribander was very poor.
> Even if the DDRR antenna was 100% efficient, it has less directivity than
> a dipole. Witout directivity, it can have no gain.
No the tribander was not very poor, and it was not pointed in
the wrong direction, and the magnetic declination was used when
installed and they checked visually that it was really in the
correct direction, etc..... The two guys are also "skeptics"
and they verified and reverified.
I know it is difficult to swallow. Only explanation is that angles
were favoring the DDRR at that time. The experiment took place in
one afternoon and was not repeated to my knowledge. As I said I also
find that a little bit too much and that's an euphemism. DDRR ~ 1/4 w
in best case in my book, but that what they measured. I will discard
that as unsignificant unless repeated many times in A/B tests.
> On what band? If it is on HF then location can have much more to do with
> it than antenna gain.
Except the experiment above, all tests are on 75m.
> We seem to agree on most of this Madjid, except the groud loss issue.
> Antenna's work the way they work, and none of it is magic. The only area
> lacking in scientific data surrounds induction field effects in soil.
Yep and no yep. Formula posted earlier show that losses are connected
to imaginary epsilon and Mu. epsilon" is non negligible, Mu" is
negligible (except in lossy ferrites &Co). Even in electrolyte there
are theoretical studies showing that losses are almost entierely
dominated by Dielectric losses due to slow speed of ions in electrolyte.
I think that's what Gary explained too in some of his postings.
> From your original post, I gathered the claim was made a DDRR would beat
> larger full size antennas. of course, that is a claim we both have
> problems with, as you pointed out.
Negatif! The only claim in Boyer's article is that it performs more
efficiently than a full size quarter wave vertical. Boyer made
comparisons on his more than ideal setup (collapsing the vertical,
shorting the DDRR) and claimed that he measured that the DDRR
performed better. I will definitly say yes in reception, and most
Hams who went to Tony's place were really surprised by the quality
of reception. He definitly can hear very well, very weak stations
that very few people copy, but on transmission Hmmm...
> I can work VK longpath from my mobile with a conventional hat loaded
> vertical on 75, and I have worked VK shortpath on 160 also. That antenna
> is 1% efficient on 160 (measured and calculated data), and perhaps 15% on
> 75 (calculated). We have to be careful using over the air data.
This can be done sometimes, but it can't be done all the time.
The only thing I can say, is that I keep an open mind on
that type of antenna or any other type. If Mr shmock says
in his book that it doesn't work and he is alone, I will
question that, try to test and experiment. If it doesn't
work Okay, if it works fine. I am not selling DDRRs
and in fact will dissuade anyone from building one. It is
just a last resort, an ersatz of antenna. Real antennas
belong in the air....
Madjid, VE2GMI
w8j...@aol.com
Hi Madjid,
In article <3288D5...@cam.org>, Madjid <mbo...@cam.org> writes:
>
>Disagree, a short thick vertical with a hat or two hats center fed will
>almost certainly radiate effectively. But the field around that type
>of antenna is Highly "Electric" and losses in the ground will be higher.
>Remember? Losses are mainly Dielectric (I think we desagree on that
>too!).
We do disagree on the mechanics of ground loss, at least on frequencies
where skin depth is more than a few feet.
I'm interested in why you would say the DDRR has less fringing electric
field, and a hat vertical does. I find just the opposite is true. Could
you expand on that, or did it come from Boyer?
>> Losses will increase by a factor of two when compared to the perfect
>> groundplane case. But that may be better than a poor groundplane. In
any
>> event, if DDRR rings are replaced with disks the radiation efficiency
>> remains the same. So the antenna is understandable in this
configuration.
>
>I am not following you on that factor 2. ..--..
Because now instead of a perfect lossless ground as the other "half" of
the antenna, we have added the resistive dissipation of another identical
antenna. I assume of course the aperture of the radiating area remains the
same. If we double the linear physical size of the radiating aperture than
all bets are off, because loss resistance doubles while radiation
resistance quadruples (when normalized to one point in the system).
To keep a comparison fair, we can't change linear physical aperture.
>> I find that impossible to believe, unless the tribander was very poor.
>> Even if the DDRR antenna was 100% efficient, it has less directivity
than
>> a dipole. Witout directivity, it can have no gain.
>> From your original post, I gathered the claim was made a DDRR would
beat
>> larger full size antennas. of course, that is a claim we both have
>> problems with, as you pointed out.
>
>Negatif! The only claim in Boyer's article is that it performs more
>efficiently than a full size quarter wave vertical. Boyer made
>comparisons on his more than ideal setup (collapsing the vertical,
>shorting the DDRR) and claimed that he measured that the DDRR
>performed better. I will definitly say yes in reception, and most
>Hams who went to Tony's place were really surprised by the quality
>of reception. He definitly can hear very well, very weak stations
>that very few people copy, but on transmission Hmmm...
Then we agree on transmission.We both say Hmmmmm. I would go one step
further and say Boyer has gone beyond exaggeration with that claim.
Factually we both know a DDRR can be no better than a 1/4 wl if both are
perfect, and an 70-98% eff 1/4 wl is much easier to optimize and constuct
than a DDRR.
Since I have spent most of my life working with low noise receiving
antennas, I'd say bunk to the claims the DDRR is better for receiving
UNLESS the problem is near field coupling. In that case, the noise source
must be within the induction field coupling distance of the array. With a
physically small antenna, that is pretty close.
>> I can work VK longpath from my mobile with a conventional hat loaded
>> vertical on 75, and I have worked VK shortpath on 160 also. That
antenna
>> is 1% efficient on 160 (measured and calculated data), and perhaps 15%
on
>> 75 (calculated). We have to be careful using over the air data.
>
>This can be done sometimes, but it can't be done all the time.
No, I can't do it during the day time, hi. But I can do it any time the
band is open for most other stations.
>just a last resort, an ersatz of antenna. Real antennas
>belong in the air....
Yes, we agree. I also use "real antennas" for transmitting.
73 Tom
FORREST GEHRKE
TM> Looking for an antenna wench to raise my beams up onto the tower.
TM> It's not a crank-up, so I need a way of getting the antenna to the t
TM> thanks
TM> sil...@datasync.com
Heh! I know you meant "winch", but to get some answers
you need to tell us what kind of forces are involved.
What is the weight you are dealing with?
Winches are rated for pulling force and the price
goes up fast with that force. Another question:
muscle power or motor? If motor, what electric
power source?
//
k2bt
* RM 1.3 02583 * Computer Lie #1: You'll never use all that disk space.
r...@ham.island.net
forrest...@cencore.com (FORREST GEHRKE) writes:
> TM> Looking for an antenna wench to raise my beams up onto the tower.
> TM> It's not a crank-up, so I need a way of getting the antenna to the t
> TM> thanks
> TM> sil...@datasync.com
>
> Heh! I know you meant "winch", but to get some answers
> you need to tell us what kind of forces are involved.
> What is the weight you are dealing with?
>
Speak for yourself! I'd rather have an antenna wench than an antenna
winch any day....
Bob, VE7HS
r...@ham.island.net __|
Robert Smits _/. |\
(VE7HS) CQ CQ CQ !!! < (0)
_ /__ |
( ) <_______/
\ \/ \__