10m Challenge: Design Wire Beam (Minimalist)low height w/max gain
KQ6XA
Need a 10m beam design with maximum gain and lowest takeoff angle, fixed
direction. Center freq 28.200. Elements will be wire. Single feedline,
minimum length of 50ohm coax. Lightweight minimalist approach.
Available supports:
2 wooden poles approx 2inch diameter, 14ft high.
Available materials: plastic insulators, thin nylon rope for guy lines.
Here's the situation: will be operating QRP in a remote mountainous
region of Peru this summer. QTH is on a high treeless plateau on level
ground at elevation 14,000ft, about same height as average local
terrain. Ground is porous limestone with about a foot of soil on top.
Only band is 10m SSB/CW, running 7W and using solar power to charge
batteries. So far, my plan was to use a 3 element squashed quad. Got any
better ideas? I've got to carry all materials by backpack!
73---KQ6XA
http://207.204.29.183/kq6xa/index.htm
http://www.qsl.net/kq6xa
Fractenna
>From: KQ6XA <spamno...@qsl.net>
>Date: 2/18/99 4:57 AM Eastern Standard Time
>Message-id: <36CBE40E...@qsl.net>
Yes; a fracvert halfwave will give you 3dB over a 1/4 wave, for example.
TT8JWM used one on his Chad (20M)DXpedition and decided not to use other
antennas, because of the obvious peformance and ease of making. All you'll need
is a 1/2 wave support of some kind, say, 15 feet. You said you have this.
Otherwise its just wires and radials.
The pattern is dipole-like (albeit with gain) so you can easily put up 2 with
two poles to get some approximation to full coverage.
If you are serious--and also want to cut down on the radials and lengths, you
can use fractal radials although this may not be necessary within the context
of your constraints. Basically, you are being asked to carry a spool of wire
and a pole.
I am extremely busy but will try to get on the ham page of
http://www.fractenna.com in March. It was pubished in the DX Magazine a while
back, and 73 last summer.
Watza squashed quad? Sounds lossy and overly big
73,
Chip N1IR
ken simmons
in and 1/4 in for elements.
The wood will be cumbersome. An X beam is a simple wire beam if you are
determined to use wood.
a COMMERCIAL antenna the Hex-beam is also very light (fiberglass and wire) I
have a six meter version that weights 2 lbs.
73, Ken K5UHF
Richard Earl
the longest peice is 8 ft (only one pc.) but this can be modified to
telescope to 4 feet for portability. The longest additional peices are
5'-2". Includes SO-239 connector. Rugged ALUMINUM AND WIRE design AND
ONLY ONE ANTENNA SUPPORT STRUCTURE IS REQUIRED. Fr is adjustable without
cutting wire elements.
EZNEC Performance graphs at web site with comparisons to typical quads
and yagis are also at this web site. Click on small graphs to ZOOM for
greater detail.
SEE http://homepage.interaccess.com/~jpearl/DeltaXray.html
If you have any further questions or requests for modifications you
require I will be happy to work with you on any possible special mods.
GL es 73
Rich
W9JUC
Eric June
than a wire beam (yagi) and would be easy to pack in, just a spool of
wire and possibly some matching components. Dimensions are reasonable
at 10m. See the ARRL Antenna Book for more info.
--
Regards,
Eric June
KU6J
KQ6XA
Sounds great. If I could carry aluminum and other stuff, it would be much more
plug-and-play. We need a make-it-on-the-spot antenna. Minimalist approach.
Unfortunately, since I will be flying into Lima, going by bus, then backpacking
at high altitude with an already maxed-out load of batteries, caving/camping
equipment, and food, I have to keep the weight down to under about one pound,
and the size to about 8inches square! Hence the need for an all-wire design. The
two 14ft support poles I will use will be locally acquired and dragged about 2
miles and up 3500ft higher in altitude by mule to the base camp.
As I mentioned before, since it will be a QRP operation, I'm looking for lots of
gain in one direction. Like the kind of gain that a 3 or 4 element yagi would
produce.
Here's the existing plan so far... Can anyone come up with something better?
The 3el squashed quad design is just the standard diamond shaped quad elements,
with the sides of the diamond spread out horizontally a little further. It's
almost a cross between a quad and a delta-loop. The two poles have a rope
between them and the driven element is supported midway on that rope, with
separate guy ropes on the sides holding it in position. Bottom feed is direct
with no matching system, about 50ohms. The reflector and director are both
supported directly on the poles.
73---Bonnie KQ6XA
http://207.204.29.183/kq6xa/index.htm
W6RCecilA
> Here's the existing plan so far... Can anyone come up with something better?
> The 3el squashed quad design is just the standard diamond shaped quad elements,
> with the sides of the diamond spread out horizontally a little further.
Since each element of a quad is about one wavelength, each element of a
Yagi is about 1/2 wavelength, and since an 'n+1' element Yagi equals an
'n' element quad in performance, the choice for minimum weight seems
clear - an 'n+1' element wire Yagi.
--
73, Cecil, W6RCA http://www.bigfoot.com/~w6rca
Brian Kelly
support is required, forward gain is on the order of 4dBd and the F/B can be
up to 20dB. Keep in mind that an antenna with "only" 4dB gain is only a half
of one s-unit less potent than a good yagi with 7dB forward gain. Plus a
sloper has the advantage a much lower takeoff angle than a yagi at very low
elevations.
The driven element would be a standard 28.200 Mhz dipole 17ft 2.25" long fed
with any small coax. 25 feet of tiny RG174 would have a loss of around
1.25dB at 28Mhz, 20% of one s-unit. You really would not need dipole end
insulators as such, small diameter nylon string provides plenty of
insulation. But if you insist on end insulators buy a cheap toothbrush and
cut 1" lengths off the handle and drill the appropriate holes.
The high end of the dipole attaches to the top of the mast, higher is always
better. The other end of the dipole runs in the favored direction and gets
staked to the ground. The angle between the dipole and the mast should
preferably be around 30 degrees. Your 14ft pole won't quite make it at 30
degrees, but 45 degrees should work fine.
You then attach several, 3,4,5, more is better, "reflectors" equally spaced
around the mast to form a conical array of wires, one of which is the driven
element. These wires are also insulatd from and are attached to the top of
the supppot and the ground just like the dipole driven element. These
reflectors should be 5% longer than the driven element or 18ft 5.31" long.
If you use #26 FlexWeave antenna wire and RG174 coax you should have a
complete directive antenna and feedline system which can be coiled up into a
shirt pocket . . big shirt pocket. Small nylon pouch.
There might be a much better and taller mast available for your mission. The
backpack QRP guys are using an antenna called the "St. Louis Vertical", the
structural basis for this whizzy antenna is a cheap ($30) 20ft fiberglass
fishing pole which collapses down to about 4ft and weighs next to nothing.
Dial into http://www.fix.net/~jparker/slvt.html and
http://www.fix.net/~jparker/w6mma.htm for the details.
Under any conditions I would build any antenna I took on a lifetime
adventure like this and install it several times in different locations and
work a lot of stations with the entire rig/antenna system before I departed.
Trudging thousands of miles then climbing to 14,000 and then finding out the
thing don't work would REALLY piss me off.
Brian Kelly w3rv
Fractenna
>support is required, forward gain is on the order of 4dBd and the F/B can be
>up to 20dB
This is an outrageous claim. Please model this antenna--at the very
least--before such info is posted.
She's not going to the sea, you know.
Chip
Brian Kelly
> >Consider a sloper array as described in recent ARRL Antenna Books. Only one
> >support is required, forward gain is on the order of 4dBd and the F/B can be
> >up to 20dB
>
> This is an outrageous claim. Please model this antenna--at the very
> least--before such info is posted.
I'm not modeling anybody's antenna for them. I used the 7Mhz sloper array at
w3wjd and it had a very useful F/B plus it boomed into wherever direction it was
switched long before hams were modeling antennas. Tell the ARRL to "model" the
thing, I quoted the gain and F/B straight out of the 16th edition (1991) of the
ARRL Antenna Book, pages 4-12 thru 4-15.
.
Dan Richardson
wrote:
Well I did here the results:
Max gain 2.7 dBi at 85 degrees.
Beam width (3 dB points) 30.6 & 136.5 Degrees
F/B ratio at 30 degrees elevation 1.17 dB.
Danny K6MHE
Brian Kelly
> >I'm not modeling anybody's antenna for them. I used the 7Mhz sloper array at
> >w3wjd and it had a very useful F/B plus it boomed into wherever direction it was
> >switched long before hams were modeling antennas. Tell the ARRL to "model" the
> >thing, I quoted the gain and F/B straight out of the 16th edition (1991) of the
> >ARRL Antenna Book, pages 4-12 thru 4-15.
> >
> >.
> Well I did here the results:
>
> Max gain 2.7 dBi at 85 degrees.
> Beam width (3 dB points) 30.6 & 136.5 Degrees
> F/B ratio at 30 degrees elevation 1.17 dB.
Doesn't sound like much a beam antenna. But your results are not at all consistent
with my hands-on observations of a real sloper array operating under real ham band
conditions or those of whoever wrote the antenna book article. I do FEA modeling in
the field of applied mechanics, I learned a long time ago to be very suspicious of
all modeler outputs as they represent reality, especially outputs from a quickie pass
at a model.
> Danny K6MHE
Fractenna
Then I will present my 20M results from 1993, in my comparisons with a dipole
at 1/2 wave, as a prelude to development of the N1IR Sawtooth.
Two sloper arrays were used, separated by 3o feet. Each had a 180 degree
reversal of orientation relative to the other. One was shorted to ground when
not in use.
Sloper Array gain: Less than 1dB over the dipole (uncertainty at least 2dB)
Sloper array F/B: 5dB at best.
Modeling allows EVERYONE to get a good handle on these numbers. Don't disparage
a valid tool--and certainly not the knowledgeable ham(s) who suggest it.
I don't blame you for pointing out the reference--only for BELIEVING it so
indiscriminantly.
73
Chip N1IR
Fractenna
>all modeler outputs as they represent reality, especially outputs from a
>quickie pass
>at a model.
>
>> Danny K6MHE
Sounds like an insult to me Danny. I, on the otherhand, have found your models
pretty good--at worst.
73
Chip N1IR
Brian Kelly
Dan Richardson wrote:
> Well I did here the results:
>
> Max gain 2.7 dBi at 85 degrees.
> Beam width (3 dB points) 30.6 & 136.5 Degrees
> F/B ratio at 30 degrees elevation 1.17 dB.
To expand a bit, I've been on the receiving end of completely bogus modeler outputs
from $15-25,000 programs like ANYSYS and RASNA, never mind the little bits and pieces
of $50-100 entry level ham antenna modeling code. Field results and testing speak
volumes more than modeling every time.
> Danny K6MHE
cbk
Dan Richardson
Boy, I sure don't know how this got posted here???? Anyway I didn't
post it. I don't do attachments in the newsgroups.
Danny, K6MHE
KQ6XA
> Since each element of a quad is about one wavelength, each element of a
> Yagi is about 1/2 wavelength, and since an 'n+1' element Yagi equals an
> 'n' element quad in performance, the choice for minimum weight seems
> clear - an 'n+1' element wire Yagi.
Thanks for your insight, Cecil. It's true that the wire for a yagi weighs less than a
quad of same gain. But does the complexity and additional cord supporting a wire
yagi, and the crossarms needed to arrange it for horizontal polarization, negate the
difference? The supports I have access to are not quite high enough for a vertical
polarized unloaded yagi.
Again, for those tuning in late, here are my constraints:
1) 2 wooden poles 14ft high each, 2 inch diameter
(available at the site). These can be arranged in
any configuration as support structures.
2) Wire, feedline, nylon cord must fit in 8square inch bag
carried by backpack, and weigh less than about 1 pound.
3) Design frequency about 28.3MHz.
4) Feedline length approx 20ft max. (RG-179 likely).
5) Low tech match (please no gamma caps).
6) Nylon cord and rope for guys and wire support.
7) No trees. No Home Depot. Barren land!
8) Possible wet, windy, or snowy conditions.
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
KQ6XA
Brian Kelly wrote:
> Consider a sloper array
Need more gain. QRP.
Thanks.
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
KQ6XA
If we use a 3 element diamond-shaped quad, with the top of the wire at 13ft off the
ground, what is the best point to feed it? At the bottom, side, or top? Or doesn't
it matter? Looking for best gain at low angle radiation. Would a delta loop with
the apex at 13ft be better at this low height? The delta loop would be easier to set
up, and take a little less rope. At any rate, some part of the wire of a delta loop
or quad will be very close to touching the ground.
The ground in this case is cracked limestone karst with a top layer of sparse grass
and soil about 3 to 12 inches deep. Soil conductivity is unknown.
73---Bonnie KQ6Xa
http://www.qsl.net/kq6xa
KQ6XA
> Have you considered a rhombic?
Yes. But it requires 4 supports and a lot of wire. Even a vee beam would
be lots of wire and 3 supports. See my other postings for what my
constraints are.
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
Gary Ferdinand
cent worth.
You clearly are in need of high gain and low angle of radiation. The
various suggestions for single-support slopers will not suffice. Nor are
you terribly concerned about front to back ratio - hi! Phased verticals
could work nicely, but with the associated support needs, phasing complexity
and radial messiness. From what you've been writing, something
constructionally-simple is also important.
Your idea for a quad is reasonable in terms of the gain and angle but has
some construction complexity. Have you thought of a wire yagi constructed
as follows. I have used such an antenna (on 40 meters!) on Field Day on
several occasions. (The club won last year in the 3A catagory, so I know it
works.)
The overall notion is to use your two supports to support the ends of rope,
which is strung between the supports to act as the yagi's boom. You will
need rope guying on each support to work against the tension of the rope
boom. Wire elements are then attached to the rope boom. Each element is
draped/strung from the boom to a convenient ground attachment point at as
gradual an angle as you can get. Attach twine to each element end and
start walking. Each element, when viewed along the boom axis would thus
appear similar to be an inverted vee. As with the vee, the greater the
angle between each half element, the better.
Such an antenna can support as many or as few parasitic elements as you wish
to string. Use very light weight feedline (and short) so as not to drag
down the rope boom. RG8X or RG58 weight coax or lighter, kept short;
dress it directly down to the ground and then run it to wherever it needs to
go. That minimizes the weight of the coax as seen by the boom.
If you are interested, I could model the beam for you and come up with some
measurements. You would still need to build it "at home" and tune it up a
bit. Given 28 MHz plus your need for but a single frequency for transmit, I
anticipate none of the bandwidth/boom length/gain gyrations that I went
through at 40 meters to get a good 50 ohm feedpoint (quite possible with a
long boom)! I should think a boom length of about 3/2 wave with 4 elements
(reflector, DE and two directors) would probably meet your needs. As I
said, I did this for 40 meters and ended up with a 50 ohm feedpoint, 10dbd
gain and 50 KHz bandwitch; I see no reason why it shouldn't work for 28 MHz.
The only issue I foresee would be keeping the proper tension on the rope
boom to support the coax. Two tight guys on the back each run off at 120
degrees, with the boom acting as the third "guy" at 120 degrees ought to
work. If you're worried about tension snapping the 2 inch "locally
acquired" wood supports, you could alway run the rope boom over the support
and beyond to a ground stake (rock) way beyond, thereby apply some of the
stress to the stake and relieving the support a bit. The wire elements
themselves, if you use that very narrow gauge braided copper wire, weigh
next to nothing. I'd use twine (not rope) to stretch the elements out and
fasten to a ground stake (or rock - there's plenty of those around in karst,
right?). Also, it doesn't rotate that easily, but I should think the
entire USA is pretty much in the same direction as viewed from Peru (haven't
checked to be sure...). Biggest concern again to me would be how to find
guy stakes/rocks suitable to keep it together. I don't imagine you have
many trees or well-rooted shrubs at 14,000 feet MSL.
Gary W2CS
Apex, NC
KQ6XA wrote in message <36CBE40E...@qsl.net>...
Gary Ferdinand
keyboard does that...
Gary W2CS
Gary Ferdinand wrote in message ...
KQ6XA
> Lash the two poles together to form a 25 foot mast,
> use to support an inverted Vee. This will have a lower
> takeoff angle, and ground gain, compared to anything
> you can do at 14 feet with a quad or yagi. There's no
> substitute for height.
Hmmm. Is that really the case? What do you mean by ground gain?
Anyway, if we lashed the 2 poles together, I could make a 5/8wave vertical,
with radials spread on the ground. That might give more gain and low angle
radiation than an inverted V. But I'm looking for more useful gain than
that if possible. The challenge and objective is to make a beam with more
than just unity or dipole gain for my little QRP HT.
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
KQ6XA
> Have you thought of a wire yagi constructed
> as follows. The overall notion is to use your two supports to support the
> ends of rope,
> which is strung between the supports to act as the yagi's boom. each element
> is draped/strung from the boom to a convenient ground attachment point at as
Great, Gary.Sounds like a cross between a wire yagi and a wire inverted V yagi.
The cord or twine on the ends of the elements would have to be fairly long, but
that's probably OK. It certainly would get the feedpoint and centers of the
elements up at max height. The feedline I will use is very light weight (RG179).
I hope to minimize the length of feedline because of loss.
> I don't imagine you have
> many trees or well-rooted shrubs at 14,000 feet MSL.
You're right, Gary. No trees and very few shrubs. The grass that grows up there
is like astroturf. The soil in many places is non-existent.
Oh I just thought of one more thing that may give some indication of the ground
conductivity or absorption at 10m. We have been able to successfully talk
through this type of rock before on 27MHz using HTs between cavers several
hundred feet below, and the surface. There is a lot of air spaces in the cracked
rock.
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
Gary Ferdinand
wondering is whether (assuming dry for the moment) this soil really looks
like soil, electrically. I'm speculating that your electrical height above
ground might be quite high as a result, giving you a very low angle as a
result. I'm going to have to research that one a bit -- intriguing.
In any case I hope you post whatever you end up deciding to use. This has
been an interesting thread that could benefit from any concluding remarks
you might have time to post. 73.
Gary W2CS
Apex, NC
Gary Ferdinand
height at which to have a well-defined pattern. Depending on ground
conductivity it could actually "look" much higher. Considering her need for
something like 10db gain and her constraints, a gain antenna at 1/2 wave
high is probably the best she'll be able to erect, IMHO.
Gary W2CS
>Lash the two poles together to form a 25 foot mast,
>use to support an inverted Vee. This will have a lower
>takeoff angle, and ground gain, compared to anything
>you can do at 14 feet with a quad or yagi. There's no
>substitute for height.
>
>Gary
>Gary Coffman KE4ZV | You make it |mail to ke...@bellsouth.net
>534 Shannon Way | We break it |
>Lawrenceville, GA | Guaranteed |
Brian Kelly
KQ6XA wrote:
> Brian Kelly wrote:
>
> > Consider a sloper array
>
> Need more gain. QRP.
OK, but gain is awfully hard to come by for real backpacking
portability. I suggest that you not get too wrapped around gain numbers
as such. A 6dBd gain antenna is a pretty significant antenna and all
you get is a single s-unit improvement. When push comes to shove, having
an S7 signal with some fairly sophisticated antenna vs. an S6 signal
with a simple dipole simply is not worth the hassles and does nothing to
add to the actual communications effectiveness. On 10m especially the
propogation characteristics of the moment play a much greater role than
the antenna in whether you have the qso or not. At this point in the
sunspot cycle you can expect to have what many would consider an amazing
signal from 7 watts with any antenna IF the path is open. If the path is
not open a couple kilowatts into stacked long boom yagis on a 200ft
tower won't get you much past the horizon.
Of course these days apparently an antenna won't work unless it's
modeled first, so don't miss that step. Heh-heh!
KQ6XA
> Of course these days apparently an antenna won't
> work unless it's modeled first, so don't miss that step. Heh-heh!
I just modeled a few in my quadruled notebook. Tee hee... :-)
Actually, whatever we decide upon, we plan to build here and try before the
expedition.
73---Bonnie KQ6XA
KQ6XA
> Very interesting, Bonnie. I'm wondering about this "soil."
> I'm speculating that your electrical height above ground
> might be quite high as a result,
Also, we will be camped on a plateau at the top of a 3000ft cliff. I may be
able to position the antenna (and hence my tent) fairly near the "edge", or
near the part that slopes northward...but I'll have to be careful about that
:-)
> In any case I hope you post whatever you end up deciding to use. This has
> been an interesting thread that could benefit from any concluding remarks
> you might have time to post. 73.
Of course, Gary! Actually, once the antenna is built and tested here before
the expedition, I plan to post my results as well.
Anyone who cares to hear the *real* results can certainly tune in for a QSO on
10m in July/August. That is if there is anyone out there on this group who can
work me in Peru on their "modeled" antennas... only kidding, only kidding...
:-)
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
KQ6XA
> Ever consider a groundmounted vertical beam?
Thank you, Dick, for that suggestion. It deserves some follow up. What you
described was a parasitic 1/4wave vertical array, not phased, right?
That certainly sounds very attractive from the standpoint of height and ease
of setup. How about the gain of such an array? Is it comparable to a 3 element
quad or 4 element yagi? I tried to make one of those vertical arrays before
(like 20years ago) but as I remember, I couldn't get it to give me much gain.
Seemed like the parasitic elements weren't doing their job or something. Maybe
it was just my setup or ground clutter in the near field at the time. It was
for 40m, and I just ended up phasing the verticals instead.
Do you have experience using this type of array, and what kind of comparison
would you make to a horizontal yagi at 1/2 wave high?
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
Gary Coffman
>Again, for those tuning in late, here are my constraints:
>1) 2 wooden poles 14ft high each, 2 inch diameter
> (available at the site). These can be arranged in
> any configuration as support structures.
>2) Wire, feedline, nylon cord must fit in 8square inch bag
> carried by backpack, and weigh less than about 1 pound.
>3) Design frequency about 28.3MHz.
>4) Feedline length approx 20ft max. (RG-179 likely).
>5) Low tech match (please no gamma caps).
>6) Nylon cord and rope for guys and wire support.
>7) No trees. No Home Depot. Barren land!
>8) Possible wet, windy, or snowy conditions.
Lash the two poles together to form a 25 foot mast,
Dick Carroll
you good gain, ground mounting and a low takeoff angle. You
could cut the 2- 14ft poles in half and have 4- 7ft guyed
vertical supports for a 4 element groundmounted beam. Use
wire elements which are made of, maybe #22 or #24 copper
magnet wire thumbtacked, stapled, or tied to the wooden
uprights. Element length, over a foot longer than the 7 ft
poles, would need to be adjusted to the proper length for
each element, possibly by using 4 thin collapsable portable
radio antennas 18 inches or so in length. They could be
wiretied to the tops of each support and connected to each
wire element with an alligator clip soldered to the end of
the element wire. Yhey would make element length adjustment
a snap. Or a stiffer wire that would stand up far enough
above the 7ft support to complete the element length (8ft+)
would work. 4- 18inch pieces of Rat Shack aluminum ground
wire cold be carried rolled up, and trimmed on site, or
sized in advance. I'd carry a few small staples and some
nylon wireties (can be used as insulators also) along.
Set element lengths and spacing for that of a 4 element
yagi beam.
For the counterpoise, use a single piece of magnet wire
long enough to lie on the ground from 8 ft behind the
reflector past all 4 elements and 8 ft in front of the first
director. Use 4 pieces of wire 16ft long at right angles
placed at each element and connected to the first, the long
wire. All wires can be precut, compactly rolled and tied for
carrying, and assembled on site. Small, light copper magnet
wire is ideal.
If you plan to transmit in one direction, it could be set
up and left alone, but if a change in directions is needed
one would need to move the directors and the reflector and
the counterpoise, leaving the driven element in place. with
the directors and reflector removed, you'd have an
omnidirectional 1/4 wave vertical.
You may find you need to provide a better match for the
feedpoint, if so use a small 4:1 balun (Palomar sells a line
of very compact lightweight efficient baluns) But I've used
3 and 4 element yagis directly fed with 50 ohm coax with
good results. There are some other ways to obtain a good
match in the literature. You might want to do some testing
to see what works out at QRP beforehand.
In fact I'd set up and test a clone of this antenna well in
advance of the trip, then disassemble it and roll up the
elements and counterpoise for packing to take along. If at
all possible I'd pack along one of the pencil butane
torch/solder iron units, a can of fuel and a bit of solder.
It'll be indespensible.
This seemns like a lot of bother but it should provide an
antenna with good directional properties and good gain which
requires very little in parts to be packed into the back
country. Hey, I may make one of these myself just to see how
it works out.
If you can get along without gain, do as Gary Coffman says
and make a drooping dipole and hang it as high as possible.
Dick W0EX
Dick Carroll
>
> Watza squashed quad? Sounds lossy and overly big
You sure he's not referring to a Fractal quad? That's the
first thing that leaped to mind.
Dick C
Fractenna
>modeled first, so don't miss that step. Heh-heh!
Strike that Brian: should be 'understood properly'.
73
Chip N1IR
Fractenna
suggestion. Given that, I can hardly be expected to help with any suggestions
on a FQY, and there is already a forum where such things are discussed. I'm
not going to spend time competing against poor designs for attention. Don't
need the hassle and the 'guilt by association'.
73
Chip N1IR
Gary Coffman
>Gary Ferdinand wrote:
>
>> Have you thought of a wire yagi constructed
>> ends of rope,
>> which is strung between the supports to act as the yagi's boom. each element
>> is draped/strung from the boom to a convenient ground attachment point at as
>
>The cord or twine on the ends of the elements would have to be fairly long, but
>that's probably OK. It certainly would get the feedpoint and centers of the
>elements up at max height. The feedline I will use is very light weight (RG179).
>I hope to minimize the length of feedline because of loss.
>
>> many trees or well-rooted shrubs at 14,000 feet MSL.
>
>is like astroturf. The soil in many places is non-existent.
>conductivity or absorption at 10m. We have been able to successfully talk
>through this type of rock before on 27MHz using HTs between cavers several
>hundred feet below, and the surface. There is a lot of air spaces in the cracked
>rock.
Given this situation, I think I'd go with the other Gary's idea of a rope boom
horizontal beam. My comments about antenna height were considering a
much more normal soil type. In that vein, it is worth noting that if you build this
beam here in the US to try it out, it may behave much differently here than it
would over that sort of soil. I'd expect less gain, and a depressed feedpoint
impedance with the soils here compared to there. Be prepared to rematch
it in its final location.
Brian Kelly
> 14 feet is remarkably close to 1/2 wave high. That's not an unreasonable
> height at which to have a well-defined pattern. Depending on ground
> conductivity it could actually "look" much higher. Considering her need for
> something like 10db gain and her constraints, a gain antenna at 1/2 wave
> high is probably the best she'll be able to erect, IMHO.
>
> Gary W2CS
I agree, but Bonnie is looking for directive gain which a monopole antenna will
not provide. My experiences with half wave verticals and inverted Ls both with
and without radials have all been uniformly successful and no other antenna is
as easy to build or replicate onsite. To make the 14ft pole a true voltage fed
1/2 wave vertical I'd wrap the wire around the wire a few times to keep it from
blowing around then pull a 3.44ft long tail of wire off the top of the pole to
make it an inverted L of sorts. The tuner could be a weenie MFJ unit or better
yet some tiny tuner built into a plastic pill bottle or some such, use an
equally tiny homebrew field strength meter to tune the whole thing.
There are collapsible 20ft fiberglass backpacker's fishing poles out there and
she could wrap 208 inches of wire around one of those and have a real no brainer
low angle 3dB. gain boomer.
Brian Kelly w3rv
Fractenna
>I agree, but Bonnie is looking for directive gain which a monopole antenna
>will
>not provide.
Not correct. A fractal monopole can indeed be configured for gain and directive
pattern.
73
Chip N1IR
Reg Edwards
>> for gain and directive pattern.
No sensible person would dispute the fact. But the
question arises - by how much ?
I am particularly interested in the groundwave and
low-angle radiation patterns.
Please give us some figures. Don't disappoint us again by
saying we must wait a few more months before the Fractal
website is updated. What's the big secret ?
Reg Edwards
KQ6XA
> Be prepared to rematch
> it in its final location.
You're right, Gary, that's probably the case.
At any rate, all the info so far points toward going with some sort or multi-element
beam.
3 elements or more. Trying for 9 or 10dBd, and a takeoff angle below 20degrees.
Anyone know of an SWR meter that is the size of a pill bottle? :-)
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
KQ6XA
> I am extremely busy but will try to get on the ham page
Hi Chip, looks like you're back, so I'll reply now.
> Watza squashed quad? Sounds lossy and overly big
A full wave loop of wire that is part way between a quad loop and a folded dipole.
In between. Rhombus shaped.
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
KQ6XA
> Yes; a fracvert halfwave will give you 3dB over a 1/4 wave, for example.
Sounds like a good antenna, but I need more gain. I can get more than that using
some kind of parasitic array, with the same number of support poles.
How easy would it be to arrange 2 of those fracvert halfwaves in a parasitic array,
and would it give more gain than a 3 element quad?
Looking for about 9 to 10dBd and low takeoff angle if I can get it.
I'll be QRP, and not "rare DX" like TT8JWM, so the big gun stacked array guys will
be uninterested in talking with me, since I won't be running pileups. We will be
needing daily SSB communications and phone patches with stations running only 3 to
5element beams here in the US.
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
Fractenna
>low-angle radiation patterns.
>
>Please give us some figures. Don't disappoint us again by
>saying we must wait a few more months before the Fractal
>website is updated. What's the big secret ?
>
>Reg Edwards
>
Done my duty Reggie.
Published in DX Magazine March/April 1997. 73 Magazine, Sept 1998.
The secret is out. That's why TT8JWM used it exclusively on his Chad DX
Pedition.
But, of course, you know that.
73
Chip N1IR
Reg Edwards
others I do not have access to such obscure publications.
Never heard of them. And if we had heard of them how can
anyone gain access and reprints ? And if we knew how to
gain access and reprints would it be possible to obtain
them before everyone has lost interest at some distant date
in the next millenium ?
Don't do a Hately on us. Please broadcast a few figures on
this, the most appropriate newsgroup, before readers begin
to suspect the data doesn't exist. We are not interested
in expensive, doubtful, number-crunching computer
programs, not available to non-US citizens. Just provide
us with a few facts and figures now. It would require very
little effort. One place of decimals would be fine.
There's no need to commit yourself too deeply at this
stage.
Open up. What's the secret ?
Reg.
Fractenna
>gain
>From: "Reg Edwards" <G4fgq...@btinternet.com>
>Date: 21/02/99 20:09 Eastern Standard Time
>Message-id: <01be5e43$90571b00$9afbabc3@default>
Hello Reggie--
Shall I assume you are responding to me?
My, My; we HAVE come a LONG WAY in 3 years. Why; one could ALMOST IMAGINE that
you were not aware of the many threads we have stage here on JUST THIS SUBJECT
back in 1997. And the HATELY reference: What a gem! Nothing like pretending
this is the very first you've heard of it--and to insinuate some NEW PHYSICS;
some IFFY junk science; to compare a SIMPLE vertical to a an electrically short
antenna with limited possibility of validity--at best!
Good show ol' chap!
M a n i p u l a t i o n par excellence!
Of course, it's utter bilge from you again Reggie.
Nope; nothing obscure about those pubs. And no reason to waste time REPEATING
the same ol' thread ol' Reggie. You will just have to thrust a stiff upper lip
and wait for me to find some time to put this antenna on the web site which is:
What a great pity I haven't come a cropper!
Cheers,
Chip N1IR
Fractenna
>A full wave loop of wire that is part way between a quad loop and a folded
>dipole.
>In between. Rhombus shaped.
>
>73---Bonnie KQ6XA
Hi Bonnie--
Oh yes;
Never heard it called that.
I became interested in this in 1991 when I got a JA's QSL which has a pic of a
30M 'squashed quad'(as you say) on it.... so is the point now how it fairs as a
vertical array (close to the ground)?
73
Chip N1IR
Fractenna
>using
>some kind of parasitic array, with the same number of support poles.
>How easy would it be to arrange 2 of those fracvert halfwaves in a parasitic
>array,
>and would it give more gain than a 3 element quad?
>
>Looking for about 9 to 10dBd and low takeoff angle if I can get it.
>I'll be QRP, and not "rare DX" like TT8JWM, so the big gun stacked array guys
>will
>be uninterested in talking with me, since I won't be running pileups. We will
>be
>needing daily SSB communications and phone patches with stations running only
>3 to
>5element beams here in the US.
>
>73---Bonnie KQ6XA
>http://www.qsl.net/kq6xa
>
>
Yes; easy to set up parasitically, although I have not published that yet. I
also have something called a 'goal post' array but that is pahsed and not
parasitic.
10dBd sounds too high for a 3 element quad over poor ground. Anyone model that
for you yet?
73
Chip N1IR
defau...@domain.com
What about a LPVA Array as in the ARRL Antenna Book (18dBd on 28Mhz) ?
Regards.
KQ6XA wrote:
>
> Brian Kelly wrote:
>
> > Consider a sloper array
>
> Need more gain. QRP.
>
Fractenna
>What about a LPVA Array as in the ARRL Antenna Book (18dBd on 28Mhz) ?
>
>Regards.
No log periodic is 'minimalist' ;-)
73
Chip N1IR
KQ6XA
> I became interested in this in 1991 when I got a JA's QSL which has a pic of a
> 30M 'squashed quad'(as you say) on it.... so is the point now how it fairs as a
> vertical array (close to the ground)?
Hmmm. I don't remember exactly where I first ran into the squashed quad, but I
lived in Japan for 3 years in the 60's... maybe it was then. What do they call it
in english?
In my case, the rhombus would be wider than it is high.
This would raise the height of the radiation center somewhat.
It would be horizontally polarized, thus fed at the bottom corner.
So the impedance would be higher than a quad of the same number of elements.
The only thing is, that due to this shape, it may not quite have the advantage in
gain that a quad has over a yagi. (And the generalistic analogy that a single quad
loop is similar to being two dipoles separated by almost a quarter wavelength...
the separation advantage goes away in the case of a narrow rhombus).
But a slight squashing of the quad loop might be a good compromise at low heights
above ground...
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
KQ6XA
> 10dBd sounds too high for a 3 element quad over poor ground. Anyone model that
> for you yet?
Rich, W9JUC modelled the difference between feeding the quad at the side corner
and at the bottom. In his post, he mentions that the model shows that there is a
significant lowering of the takeoff angle by feeding it at the side (vertical
polarization) at low heights.
3element quad is my starting point. If I can put up more elements, and get thus
get more gain, with the materials and constraints that I will have, I intend to do
so.
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
KQ6XA
> What about a LPVA Array as in the ARRL Antenna Book (18dBd on 28Mhz) ?
Hi DeFault,
What is an LPVA?
Log Periodic Vertical Array?
18dB sounds good to me! How many elements are needed for 18dB?
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
KQ6XA
We really will use this antenna!
Need a 10m beam design with maximum gain
and lowest takeoff angle, fixed direction.
Single feedline, minimum length of 50ohm coax.
Lightweight minimalist approach.
Available supports: 2 wooden poles
approx 2inch diameter, 14ft high.
Available materials: plastic insulators,
thin nylon rope for guy lines.
Here's the situation: will be operating QRP
in a remote mountainous region of Peru this summer.
QTH is on a high treeless plateau on level
ground at elevation 14,000ft, about same height
as average local terrain. Ground is porous
limestone with about a foot or less of soil on top.
Only band is 10m SSB/CW, running 7W and using
solar power to charge batteries. So far, my
plan was to use a 3 element quad.
Got any better ideas?
I've got to carry all antenna materials (except
the 2 support poles) by backpack in an 8inch
nylon bag with total weight about one pound!
73---KQ6XA
http://www.qsl.net/kq6xa
Richard Earl
Here is my proposal for dimensions and specs for your quad.
10 METER DIAMOND QUAD FOR PERU DXPEDITION
DRIVEN ELEMENT
SIDE DIMENSION = 8' 9 -1/4"
APEX ELEVATION AT 13'-10"
BOTTOM ELEVATION AT 1' 5-1/8"
HORIZONTAL CORNERS ELEVATION AT 7' 7-1/4"
ELEMENT SPACING 3' 5-1/2" (1/10 wavelength)
REFLECTOR SIDE
DIMENSION = 9' 0 -1/4"
APEX ELEVATION AT 14' 0"
BOTTOM ELEVATION AT 1' 3-1/8"
HORIZONTAL CORNERS ELEVATION AT 7' 7-1/4"
FEED AT EITHER HORIZONTAL CORNER ( AT 7' 7-1/4" ELEVATION) OF THE DRIVEN
ELEMENT 50 OHM INPUT
RESONANT FREQUENCY AT 28.250
SWR 1.03:1
Z= R 50.6 - X 0.9
BANDWIDTH (2:1 SWR) FROM 28.05 MHZ TO 28.5 MHZ
GAIN @RESONANCE 4.95 dBi
FRONT TO BACK RATIO 8.46 dB
TAKEOFF ANGLE 20 DEGREES
You are not listed on my QRZ CDROM please confirm you current mailing
address and I will send you print-out with graphs and dimensions for the
above. I do not have provisions for attachments to email.
GL es 73/88
Rich
W9JUC
http://homepage.interaccess.com/~jpearl/DeltaXray.html
Richard Earl
Forgot to include 3dB beamwidth = 87 degrees should cover all of the USA
with a heading of 340 degrees.
Richard Earl
Just ran some models with the apparent ground lower than grade level and
found that it can only get better with these dimensions.
As apparent ground drops, the resonant frequency rises to about 28.4 mhz
with the gain increasing, the F/B decreasing, the takeoff angle lowers,
and the swr increasing only slightly. Still an acceptable SWR with
operating freq at 28.2mHz but you probably will need to QSY anyway
because this is the operating freq of the Pacific Rim Beacon network. In
addition you will be able to operate SSB at 28.4 mHz.
In any case, build the prototype and try at various elevations at your
current QTH.
GL (again) es 73/88
Rich
W9JUC
KQ6XA
> Here is my proposal for dimensions and specs for your quad.
Thanks for all the modelling, Rich. After reading it, It certainly feels
like the quad will be my 1st choice at this point; followed by 2nd
choice---a droopy yagi and then 3rd---a ground plane or two. After going
over the system again, the "boom length" (distance between the poles) could
easily be about 15ft or maybe a little more. This should be enough for 4
elements, right? I plan to feed the driven element on the side corner for
vertical polarization, as you suggest. The impedance might even be a good
direct match for 50ohms with this spacing and number of elements.
73---Bonnie KQ6Xa
http://www.qsl.net/kq6xa
Richard Earl
Here's a 4 element quad with 50 ohm input.
I checked various depths of apparent ground up to 10 feet below grade.
With the ground change specs the differences were:
Fr changes from 28.4 to 28.45 mHz
2:1 Bandwidth changes from (28.075 to 28.775 ) to ( 28.2 to 28.9mHz)
Gain increased by 2dBi
F/B decreased by 4 dB
SWR at Fr changed from 1.01:1 to 1.07:1
Takeoff angle decreases by 4 degrees
With the center of the Array at 7'-7" above grade. ( real ground at 0
elevation)
Reflector
Apex at 14' - 0" ; bottom at 1' - 2 1/4" 4 wire sides at 9' - 0 5/8"
Driven Element ( spaced 3'- 5 3/4" from reflector)
Apex at 13'-10" , Bottom at 1'-4 3/8" , 4 wire sides at 8' - 9 3/4"
Director #1 (spaced 7' - 3" from reflector)
Apex at 13' - 8 3/8" , Bottom at 1' - 5 7/8" , 4 wire sides at 8' - 7
1/2"
Director #2 (spaced 15' - 0" from reflector)
Apex at 13' - 4 7/8" , Bottom at 1'- 9 3/8 , 4 wire sides at 8' - 2
1/2"
Fr = 28.4 mHz ; Gain = 5.8 dBi ; F/B = 18.53 dB
Z= 50 ohms ; SWR = 1.01:1 at Fr ; 2:1 bandwidth 28.075 to 28.775mHz
-3dB beamwidth = 66 degrees ; Takeoff angle = 18 degrees
GL es 73/88
Rich
W9JUC
http://homepage.interaccess.com/~jpearl/DeltaXray.html
KQ6XA wrote:
Richard Harrison
Peru this summer.
I`ve trod the altiplano and sailed Lake Titicaca.
This summer here is winter there. Often it is damp and chilly. I`ve
waited a week for weather to clear to fly out of La Paz, Bolivia.
The altitude is stunning. Natives have greater lung capacities than
lowlanders as a Darwinian adaptation. You probably won`t want to hike
far, much less carry things. For the better part of a week you will
likely sit around a lot.
I`ve put in radios in various South American countries. You may need
help. Politics and business is as corrupt as it is here. They just don`t
try so hard to hide it.
You pay gangs not to throw rocks at your airplane when you park it. You
pay a street person to watch your car while it is parked.
I needed a leased phone circuit in La Paz. The waiting time was seven
years! I had to have it in days, The phone workers were all out on
strike, spaced out in the street in front of headquarters on coca leaves
and alcohol.
Someone sent a case of whiskey to the minister of communications, and
another case to the president of the phone company, and I had my
installation order. Of course, I had to recruit and hire my own
installation crew from the strikers in the street and send them by taxi
to the various junction boxes to make the connections. The crew swiped
one of the leased circuits from an Ex-Presidente of the Republica. They
said he wouldn`t need it anymore.
Now, about radio in the Andes. Soil conductivity is sorry, unless you
are on the moist lake, ocean, or river side. We avoided working antennas
against ground.
Our typical Andean radio was a Collins 30K5 transmitter, a Collins 51-J
receiver, and a 1/2 wave dipole. Well it was a 1/2 wave at the most used
or some lower frequency. We tried hard to get the antenna up at least
1/4 wave and usually tried to get it up 1/2 wave or even more.
We used RG-8/U, and found no advantage to baluns or other complications.
It worked.
We also used 33 MHZ and 150 MHz FM for line-of-sight, and more. I put up
33 MHz vertical dipoles at 25 feet in some fixed locations. Using
Motorola Handi-talkies, with less than 10 watts output, I sometimes
talked to a Midland, Texas oilfield supplier.
I used the 150 MHz radios to remote control some of the HF radios. I
made yagis for this.
My advice is to travel light, use balanced antennas, a beam if light
weight and collapseable, get help to get stuff through customs, get help
to carry the stuff where you want to go, and grease the right palms.
Best regards, Richard Harrison, KB5WZI
Mark Keith
>
> defau...@domain.com wrote:
>
> > What about a LPVA Array as in the ARRL Antenna Book (18dBd on 28Mhz) ?
>
> Hi DeFault,
>
> What is an LPVA?
> Log Periodic Vertical Array?
> 18dB sounds good to me! How many elements are needed for 18dB?
Alot more than you would want to deal with. Also I don't know how many
elements they are using on such a LPVA , but 18dbd seems very optimistic
to me. Compare to a full blown 4 element quad which would have what
,maybe 10-12 dbd? They are gonna need a lot of elements. Just for my two
cents worth on the antennas, I kinda agree with another poster who said
to keep it simple. You don't want to have something finicky to deal with
out in the boonies. If I was going to run 7 watts on 10m camping, I
would take wire to build a good wire antenna for 10m such as an extended
double zepp, or a array of half waves, or maybe a set of phased dipoles.
But with the phased dipoles you would have to consider phasing lines. An
extended double zepp would probably be the easiest route of those. Has
appx 3 dbd broadside. This would effectively turn your 7 watts into 14
in two directions. You might also consider a lazy H style wire beam. It
would have a little more gain in two directions and could be fed with
transposed ladder line. Lot's of options I guess really. Also a trusty
5/8 gp is hard to beat on 10m, but I don't know if you can pack
something like that. But would give you a good low angle signal which is
really what you want whatever you go with. I do a whole lot of camping
and mobile ect here. I find it really doesn't take a whole lot to make
it on 10m. Either the band will be open or it won't. Power and gain
won't have a whole lot of bearing except to give you a little better
report. I've sat in the car many a time on 10m using just a no gain
mobile antenna and worked the world. MK
--
http://web.wt.net/~nm5k
KQ6XA
> Also a trusty
> 5/8 gp is hard to beat on 10m, but I don't know if you can pack
> something like that. But would give you a good low angle signal which is
> really what you want whatever you go with.
Yes, Mark, A ground plane will be my first antenna once I get there, expanding
to more exotic arrays as I have the energy to put them up...I may be able to
get a 5/8wave going, but most likely it will be a 1/4wave to start. Zepps and
other types of dipole-like arrays wouldn't be much better than a 5/8wave
vertical IMHO, so it's looking like after the gp the next step will be the
quad. Rich W9UJC has posted a couple of good quad designs.
I've done a lot of remote portable operation before, mostly with dipoles or
verticals. This trip, I'll have the time to put up something decent to get
phone-patch quality, instead of being just "readable".
73---Bonnie KQ6XA
Mark Keith
> I've done a lot of remote portable operation before, mostly with dipoles or
> verticals. This trip, I'll have the time to put up something decent to get
> phone-patch quality, instead of being just "readable".
The rope stingable beam seemed like a pretty good idea. Having the
supports would be the tricky part. With no trees, you don't have a lot
of premade supports. I'm sure you will come up with something to work. I
think for the most part you should do ok. I remember I used to use a old
yeasu ft -7 a few years ago. It was only about 10 w, and never had any
trouble getting out with it. I used to camp and run 40 and 75 ssb with
it. Actually did pretty good with only 10w.MK
--
http://web.wt.net/~nm5k
Matt Meola
[ ... ]
> Your idea for a quad is reasonable in terms of the gain and angle but has
> some construction complexity. Have you thought of a wire yagi constructed
> as follows. I have used such an antenna (on 40 meters!) on Field Day on
> several occasions. (The club won last year in the 3A catagory, so I know it
> works.)
[ ... ]
Gary, have you ever considered using twin-lead instead of just wire?
Each element would effectively be a thin-quad, or a folded dipole.
NEC2 seems to be impressed with it, at least on 2m...
--
Matt Meola (matt....@usa.net) KC0DXW
Bailey, Colorado
"Gun control means using two hands."
Roy Lewallen
>
> Gary, have you ever considered using twin-lead instead of just wire?
> Each element would effectively be a thin-quad, or a folded dipole.
>
> NEC2 seems to be impressed with it, at least on 2m...
Be careful modeling twinlead with NEC-2 or MININEC, or programs using
them. They don't take the insulation into account. You'll probably get
a reasonable representation of what the antenna is capable of, but the
elements of the real antenna will have to be around 3% shorter than
the program predicts (due to the effect of the insulation on the
antenna, or common-mode current), and the feedpoint impedance will be
off a bit because of the failure to take the slower transmission-line
velocity factor into account.
You folks might be interested in my favorite FD antenna, which is made
with twinlead elements. It's light weight, unidirectional, easily
direction-switchable, and can usually be made to present a good match
for 50 ohm line. You can get more information at
http://www.teleport.com/~w7el.
Roy Lewallen, W7EL
Richard Harrison
I think you are in luck to have Eucalyptus poles on-site. All you need
is a big roll of wire and some rope to guy the eucalyptus poles.
Put up a 10-meter rhombic and you can forward scatter enough energy to
make your own band opening, perhaps. Construction is simple. Gain is
high. You don`t even need a terminating resistor. You don`t care if it
works in both directions. You will need to match 700 ohms or so, but you
are going to operate QRP, so no big deal. You will always have a
rockpile where you are going, so you can wieght down your anchors and
firm-up your antenna supports with piles of rocks. I can`t think of
anything simpler or more effective, even if it is a little large.
Eric June
7100 feet we always have at least a couple of trees to tie the antennas
off to.
I'd have to go with the other poster who suggested an inverted-V beam.
You erect your two poles, have them support a thin rope between them,
and use the rope to hang your inverted-V's from. One is fed at the apex
(at the rope) and the other are parasitic elements, a reflector and as
many directors as you wish to pack and can fit on the rope. The
parasitic elements are basically just pieces of wire, cut the
appropriate length for reflectors/directors, and tossed over the rope,
tied off at the ends to rocks with some string. Guy the ends of the
poles to give the rope some tension and prevent sag. Such a system
provides these advantages:
1) By using a 1/2 wave center fed dipole (V) as the driven element, you
avoid the need for an antenna tuner, VSWR bridge, or a bulky matching
network.
2) No ground radials required
3) Hard to say without modeling, but having the feedpoint up in the air
should provide some advantage vs. end-fed verticals fed at ground level,
or vertical half-wave wires fed at h/2.
4) Gain roughly equivalent to that of a Yagi with the same number of
elements
Don't worry about polarization, that only matters for ground wave
communications, not for the kind of path you are looking to cover.
By the way, use the smallest diameter wire that you feel will survive
the elements. Don't get caught up in the belief that antennas must be
#14 copper or larger. Smaller wire sizes will only increase the Q of
your antenna (reduce the bandwidth) a little bit. You are basically
setting up a single frequency point-to-point communications link, so a
loss of bandwidth shouldn't bother you too much.
--
Regards,
Eric June
KU6J
Gary Coffman
[talking about a rope boom yagi]
>1) By using a 1/2 wave center fed dipole (V) as the driven element, you
>avoid the need for an antenna tuner, VSWR bridge, or a bulky matching
>network.
Actually, not true. It would be a sign that you had poor coupling between
the driven element and the parasitic elements if the feed impedance of
the driven element approached that of a plain dipole. You'll almost certainly
need to match the driven element, just as you do with any other yagi beam.
Either a gamma match or a Tee match could be used, but a short feedline
and ATU could be used instead.
Gary
Gary Coffman KE4ZV | You make it |mail to ke...@bellsouth.net
534 Shannon Way | We break it |
Lawrenceville, GA | Guaranteed |
Richard Harrison
3-element yagi. Here is a design adapted from a 1945 War Department
manual.
The four supporting poles should be as long as possible, up to a maximum
of 60 feet.
The four sides of the curtain consist of 192 feet (each) of wire. That
would be two pieces (each) 384 feet long.
The side poles should be placed 140 feet apart.
The end poles should be placed 336 feet apart.
When suspended, the curtain should be 127 feet wide.
10 or 11 dBd is pretty good for something no more complicated than two
pieces of wire and four poles.
Fractenna
>the driven element and the parasitic elements if the feed impedance of
>the driven element approached that of a plain dipole. You'll almost certainly
>need to match the driven element, just as you do with any other yagi beam.
>Either a gamma match or a Tee match could be used, but a short feedline
>and ATU could be used instead.
>
>Gary
>Gary Coffman KE4ZV | You make it |mail to ke...@bellsouth.net
>534 Shannon Way | We break it |
>Lawrenceville, GA | Guaranteed |
>
Actually Gary, not true. You most certainly can get 50 ohms--or close to
it--with judicious use of element spacing and lengths. That's what genetic
algorithm optimization is all about.
Obvioulsy your comment is correct if the elements are close-spaced.
73
Chip N1IR
Eric June
I think you are assuming some particular Yagi design. The drive
impedance, forward gain, and front-to-back ratio are all parameters that
are open to optimizations and trade-offs by the designer. It is
possible to design a Yagi that will provide a VSWR of 2:1 or less, even
when directly fed with 50-ohm coax. You will likely give up gain and
F/B ratio to achieve this, but that may still be desirable given the
constraints of the portable operation.
Some modelling and/or experimentation would certainly be in order so as
to avoid arriving at the destination with a high-gain Yagi, drive
impedance of 5-10 ohms, and no matching circuit.
Fractenna
>gain
>From: frac...@aol.com (Fractenna)
>Date: 2/25/99 11:40 AM Eastern Standard Time
>Message-id: <19990225114008...@ng-fv1.aol.com>
I am re-posting this because it appears that Eric--and presumably
others--didn't get it on their server. If so, I suspect Eric wouldn't have
posted at 3:04PM saying the same thing.
73
Chip N1IR
Richard Harrison
10 or 11 dBd is pretty good for something no more complicated than two
pieces of wire and four poles.
Oh yes, I should have said that should 10 meters not be open, the
rhombic will radiate a respectable signal at lower frequencies. It is
relatively frequency insensitive. Alas, the gain is a function of
frequency.
Eric June
from http://www.peaktopeak.com) so I don't see things in real time. On
my last download, I guess Gary's message was there but yours was not.
Fractenna
Great minds think alike then:-)
73
Chip N1IR
KQ6XA
> A 10-meter horizontal rhombic
Now we're talkin'
> The four sides of the curtain consist of 192 feet (each) of wire.
Thanks for the rhombic dimensions. I'd love to put one of those up.
I'll keep it in mind if I can get 4 supports.
73--- Bonnie KQ6XA
http://www.qsl.net/kq6xa
Richard Harrison
design techniques are used, the "alignment" and "maximum output"
methods. "Alignment" produces smaller antennas at a price of less than
two dB in the gain department.
At Radio Free Europe, Signal Corps Rhombic Kits and one-off designs were
used. I had our propagation engineers make horizontal and vertical
radiation diagrams plus gain determinations as a function of frequency
for all of our rhombics. I felt I had wasted their time, as the results
showed much less difference between the different designs than I had
expected. The more wavelengths per side of the rhombic, the more gain.
You sort of hit the point of diminishing returns at four or five
wavelengths per side (There are four sides).
You want to get it up in the air as that tends to lower the vertical
radiation angle, and it eliminates some of the ground loss.
However, The Signal Corps advised laying the antenna out on the ground,
if you couldn`t get it erected, and start talking!
Mark A. Fuller
gain a requirement? If you could get an omni high enough, wouldn't
that be ok? I understand the height restriction is due to lack of
trees at the planned elevation and undesireablness of packing in a
mast.
However, have you considered a kite antenna?[1] You could get some
serious height, but you'd have to pack in as much tether and wire as
you anticipate flying.
[1] http://www.kitesantenna.com/xpage1.html
Mark
Second Amendment Law Library, recent legal scholarship at:
http://www.2ndlawlib.org/
Mark Forsyth
>I've been following this thread for awhile. Why is low height and max
>gain a requirement? If you could get an omni high enough, wouldn't
>that be ok? I understand the height restriction is due to lack of
>trees at the planned elevation and undesireablness of packing in a
>mast.
>
>However, have you considered a kite antenna?[1] You could get some
>serious height, but you'd have to pack in as much tether and wire as
>you anticipate flying.
Hmmm. Nothing about log periodic dipoles either. Seems to me that and lpd
with a boom/feeder length of about 11 1/2 feet, 5 elements longest about 18 feet.
Put the big end up high and peg the other end out as far as possible with extra rope.
Peg out the elements as sort of inverted V dipoles. Keep em parallel with an apex
angle of about 60 degrees.
Dunno what sort of gain it'd provide, probably not much, but with experimenting
with boom length / number of elements /element spacing you should be able to come up
with a very workable antenna.
Mark F...
jor...@santanet.com
> Lash the two poles together to form a 25 foot mast,
> use to support an inverted Vee. This will have a lower
> takeoff angle, and ground gain, compared to anything
> you can do at 14 feet with a quad or yagi. There's no
> substitute for height.
>
> Gary
> Gary Coffman KE4ZV | You make it |mail to ke...@bellsouth.net
> 534 Shannon Way | We break it |
> Lawrenceville, GA | Guaranteed |
>
I think Gary nailed it pretty good there.. I'd just like to add one small
improvement to his idea. On your dipole, run 4 wires for each leg, then get
6 large coffee can lids (plastic) and use three on each side. You poke 4
holes in each lid at the top, bottom and both sides. Feed one wire thru each
hole and go on to the next lid. Space them out along the length of that side
of the dipole, then do the same on the other side of the dipole. Make sure
you connect the wires again at the end of the dipole.
This procedure has the effect of using a large diameter of copper pipe for
each side of your dipole. Basically all the lids are doing is acting as a
spreader to get the wires apart.
If you need a picture, I can draw you one up.
Good luck, sounds like fun.. I'll be in Haiti this summer hoping to use this
antenna configuration and maybe I'll hear you.
73
Paul Jordan
KL0AN
-----------== Posted via Deja News, The Discussion Network ==----------
http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Richard Harrison
Lash the two poles together to form a 25 foot mast, use to support an
I think Gary nailed it pretty good there.
Well Paul, I would disagree with you and Gary.
You are almost three miles high already on the Altiplano. What you need
is signal strength to bridge the gap between continents when conditions
are not optimum. You need high power and high-gain antennas. If you
don`t have one, you need the other even more.
Commercial practice would include multikilowatts, rhombic antennas on
both ends, and triple-diversity receiving systems. For amateur purposes
you are forbidden the kilowatts. You at least need decent antennas. The
rhombic is ten times as good as the inverted Vee. That gives some hope
of success.
Richard Harrison
I wrote: The rhombic is ten times as good as the inverted Vee. That
gives some hope of success.
You could also think about multiplying your transmitter power by ten.
You could curtail power to prove a point anytime you felt like it. Solar
power doesn`t mean puny power. It means limited total energy, or
transmitting a smaller percentage of the time.
A 4x8-foot solar panel in the Gulf of Mexico easily lets you listen
continuously day and night and transmit 50 watts for more than an hour a
day, 365 days, and power computers and other automation equipment
to-boot. And, nobody is there cleaning the panel of salt-spray and bird
droppings. You are closer to the equator, but it is winter, so the
insolation will be different, but remember the solar supply works in the
Gulf of Mexico during winter`s short grey days. Our Gulf radios talked
automatically every three minutes, 24 hours a day, when ordered to
respond with all the latest data.
Think about transmitting 50 or 100 watts to improve your chances of
success, and just listen more than you talk.
Richard Harrison
because the antenna that gives you 11 dBd gain at 10 meters, can also
give 8 dBd at 20 meters and 5 dBd at 40 meters.
Propagation happens.
Eric June
I suggested a rhombic a few weeks ago, but what you and I missed in
their requirements is that they are limited to only two supports. This
is a treeless plain. You need 4 supports for a rhombic. Hence, Bonnie
rejected the idea.
Dick Carroll
could come up with for the requirements given might be a 2
or 3 element cubical quad. A fullwave length loop of wire
for each element, supported at the peak of each pole,
diamond mounted...the outer points and bottom point for each
element are tied off with twine. You could make this in
advance, test and prove it, then roll up the wire loops and
carry them in your pocket if needed...You can tune each
element with simple tuning stubs made from short pieces of
lighweight TV twinlead, made deliberately too long and tuned
by smipping off short lengths to resonate as necessary.
If you need a third element mount your 2 poles far apart
enough so that you can run a cord between the tops to
support the middle element without needing a third pole.
Simple homemade cubical quads work well, I've made and
used a few. Their main disadvantage is longterm sturdiness,
which shouldn't be a factor in your trip.
73, Dick W0EX
Richard Harrison
Simple homemade cubical quads work well.
Chances are, you will want to communicate and 10 meters will be dead.
Which antenna will best let you fall back to 20 meters or 40 meters?
The rhombic doesn`t need retuning. The impedance it offers your radio
will hardly change. The gain on any band will beat your quad.
The rhombic likes high altitudes, but it doesn`t stop working just
because it is near the ground.
The loss rises as it would in most antennas, but less than in some
because the rhombic`s focus comes from alignment of the lobes generated
by traveling waves on long wires.
With few exceptions, every point-to-point HF commercial radio system in
the world uses rhombics because propagation demands frequency changes
without too much hassle.
High gain is also an economic requirement in establishing an effective
signal path and rhombics are the best way to get the gain.
All you need is two pieces of wire and four supports of whatever height
you can muster and you can erect a rhombic. Oh yes, you need some rope
for securing the wires and the supports for the wires. The rhombic is a
high impedance balanced load. If your radio can`t handle that, you need
a balun or other network for the transition.
Richard Earl
Here is a 2 support (14 ft.) rhombic for your dxpedition in Peru.
Gain 10dBi F/B 28.24 Fr 28.24 mHz bandwidth 3 mHz
Take off angle 26 degrees Beamwidth 28 degrees @ Fr.
Length of each leg 70'-10" distance between poles 128'
Pull side corner tie downs until side corners are 4' 0" above grade.
Zin = 639-J23 (600 ohm) @ Fr.
For 12 watt input, terminate the front corner (at 14 ft above elevation)
with 3 ea 1800 ohm 2 watt carbon composition resistors in parallel. For
16 watt input use 4 ea 2400 OHM 2 WATT RESISTORS IN PARALLEL.
Feed with 50 ohm unbalanced to 600 ohm balanced matching network.
The matching network could be any of the following:
1. Fixed Air wound link coupled parallel network made with B&W
MIniductor and a tunable mica capacitor. See ARRL Antenna book for
details.
2. 12 to 1 toroid balun. Perhaps,someone in this NG, has a program to
give you the circuit components and winding polarity.
3. QRP antenna tuner.
Best of luck es 73/88
Rich
W9JUC
KQ6XA wrote:
>
> This is not an exercise. We really will use this antenna!
> Need a 10m beam design with maximum gain and lowest takeoff angle, fixed
> direction. Center freq 28.200. Elements will be wire. Single feedline,
> minimum length of 50ohm coax. Lightweight minimalist approach.
> Available supports:
> 2 wooden poles approx 2inch diameter, 14ft high.
> Available materials: plastic insulators, thin nylon rope for guy lines.
>
> Here's the situation: will be operating QRP in a remote mountainous
> region of Peru this summer. QTH is on a high treeless plateau on level
> ground at elevation 14,000ft, about same height as average local
> terrain. Ground is porous limestone with about a foot of soil on top.
> Only band is 10m SSB/CW, running 7W and using solar power to charge
> batteries. So far, my plan was to use a 3 element squashed quad. Got any
> better ideas? I've got to carry all materials by backpack!
>
> 73---KQ6XA
> http://207.204.29.183/kq6xa/index.htm
> http://www.qsl.net/kq6xa
Gary Coffman
On Sat, 06 Mar 1999 11:45:51 -0600, Richard Earl <w9...@juno.com> wrote:
>Hi again Bonnie,
>
>Here is a 2 support (14 ft.) rhombic for your dxpedition in Peru.
>
>Gain 10dBi F/B 28.24 Fr 28.24 mHz bandwidth 3 mHz
>
>Take off angle 26 degrees Beamwidth 28 degrees @ Fr.
>
>Length of each leg 70'-10" distance between poles 128'
>
>Pull side corner tie downs until side corners are 4' 0" above grade.
Have you done a mechanical analysis of this setup, Rich?
I'd think that the tension required in the spans to produce
an acceptable sag would be excessive for a light backpackable
array.
Richard Earl
No, I haven't Gary. but my rhombics on the west coast were 470 ft on a
leg and the sag didn't effect the performance.
The total weight for 140 ft (each side of the array) of #14 - 168 strand
wire (at 20# /1000 ft) is less than 2.8 lbs.
Bonnie take note. The weight of your rhombic now approaches 6# with
coax, balun and insulators( use cut off tooth brush handles or drilled
peices of 1/4" plexiglass available in scrap quantities from your local
hardware store- where widows are repaired -- lexan etc etc.)
Tbank you, Gary, for the stimulation of my gray matter. ( My hair is the
same color and disappearing fast.)
GL es 73
Rich
W9JUC
http://homepage.interaccess.com/~jpearl/DeltaXray.html
Dick Carroll
>
> Dick Carroll wrote:
> Simple homemade cubical quads work well.
>
> Chances are, you will want to communicate and 10 meters will be dead.
> Which antenna will best let you fall back to 20 meters or 40 meters?
>
> The rhombic doesn`t need retuning. The impedance it offers your radio
> will hardly change. The gain on any band will beat your quad.
>
Rich, I'm with you on the effectiveness of the Rhombic,
having used the one at the Fort Monmouth MARS and ham club
station way back when. I've never seen such an antenna
attract attention, on the air or just from gawkers. :-) It
sat atop four 70 ft utility poles, was a 3-wire 'fan'
configuration-a Signal Corps rhombic of the first
order.
If Bonnie can haul whatever she needs build a rhombic to the
site, I'd certainly recommend it. You may have missed her
comment that she is planning to take a QRP 10 meter
handheld, solar powered, so looks like it's 10 meters only.
If I was faced with that situation, I'd be inclined to have
at least one, and maybe 2 alternative antenna plans, all
well worked out in advance, which would all utilize the same
set of components.
Something like- #1 rhombic, #2 loop quad, #1 dipole/inv. vee
as high as possible.
73, Dick W0EX
Richard Harrison
Spacing transmission line wires more than a fraction of a wavelength
results in radiation. The longer this spacing continues, and the more
spacing between the wires, the more radiation.
If the divergence between wires is gradual in a transmission line,
little reflection of energy happens. This is the basis of the tapered
transmission line which is used for a smooth wideband impedance
transformation in many applications. The rhombic is two tapered
transmission line sections, back to back.
The rhombic has two pointy ends. The radio is connected to one of the
pointy ends, and the other pointy end is often connected to a
termination resistor. This resistor is chosen to match the terminal
spacing-determined impedance of the antenna wires.
Looking and traveling back from the resistor, the terminal impedance
will be increased as the space widens enroute to the maximum width of
the rhombic. Looking at the impedance of the rhombic as we would travel
back towards the radio from the widest part of the rhombic, we we would
see the impedance decrease again as the spacing between the wires again
decreases. Arriving at the radio, we would see an impedance somewhat
related to the termination resistance of the rhombic. The reason the
termination resistance isn`t exactly repeated is because of radiation
from the rhombic.
If there are a number of wavelengths in a transmitting rhombic, It won`t
make much difference what the termination resistance is except for
radiation in the direction from the resistance towards the radio. The
normal radiation direction is away from the radio and towards the
termination resistance. If an open or a short exists at the termination
of the rhombic, all of the energy that was not radiated in the forward
direction, as a result of the energy traveling towards the resistance,
will be reflected. Traveling towards the radio, this left-over energy
will now be radiated in the reverse direction from that produced by the
forward wave.
Most rhombics make an angle between the wires at the pointy ends of
about 40 degrees.
Like a transmission line, rhombic wires close to the Earth will suffer
loss. Any energy absorbed by the Earth is not radiated.
To get most performance from a rhombic, it should be big and high.
Richard Harrison
It (the rhombic) sat atop four 70 ft utility poles, was a 3-wire fan
configuration.
Rhombics that are going to be used for commercial or military
transmitting usually have 3 almost parallel curtains. The three wires in
each side of the curtain are connected together at their ends. At their
side supports, there is a foot or so distance between wires at their
attachnent points. This helps reduce impedance variations between
operating at one frequency or another.This means the same load on the
transmitter and maximum frequency agility.
Commercial interests almost always have separate receiving and
transmitting sites to avoid interference, especially when several
simultaneous transmissions are in progress as a norm.
You can usually tell at a glance whether you are looking at a receiving
or transmitter site. Receiving sites almost never use 3-wire rhombic
curtains, and the transmitting sites almost always do.
Fractenna
>
>
NICE description!
73
Chip N1IR
Mark Keith
> Like a transmission line, rhombic wires close to the Earth will suffer
> loss. Any energy absorbed by the Earth is not radiated.
>
> To get most performance from a rhombic, it should be big and high.
>
> Best regards, Richard Harrison, KB5WZI
I just thought of something... She could use a v beam and get alot of
gain ala rhombic with less supports maybe. You could have a long v beam
with one major support at the feed, and then run the legs way out
drooping to ground , where they could be tied off to leaders made from
rope,etc. I don't think the drooping would hurt , in fact , I think many
do that anyway. Two wavelengths a leg would give appx 7.6 dbi gain in
two directions bisecting the V. Four waves a leg= appx 10 dbi, Eight
waves = appx 12.8 dbi.
Twelve waves a leg =appx 14.4 dbi gain. This is naturally less than with
a rhombic, but seems might be easier to put up. To compare with a
rhombic at those lengths , a rhombic two waves would be appx 8.9 dbi,
four wave= appx 12.1 dbi, eight waves=appx 15.1 dbi, twelve waves =appx
16.9 dbi!!!.That will brown the food on 10 meters. MK
--
http://web.wt.net/~nm5k
Gary Coffman
>Hi Gary,
>
>No, I haven't Gary. but my rhombics on the west coast were 470 ft on a
>leg and the sag didn't effect the performance.
I was concerned due to the low height of the two supports (14 ft), and the probable
lack of adequate guy anchors, that the thing might droop too close to the ground.
The nomograph in the ARRL Antenna Book suggests a sag of 12.5 feet for a 140 ft
length of #14 hard drawn copper. Note, that sag is the result of the recomended 20
pounds of tension for #14 hard drawn copper. I expect soft stranded copper would
have a greater sag (due to the necessarily lesser tension). The rhombic shape is
to be generated solely by tag ropes tied between the centers of the spans and Earth.
I haven't done an analysis of that, but my gut feeling is that it would make matters
worse since part of the force vector of those tag lines is outward and part downward.
I think it might work better mechanically if the two support poles were at the
vertices of the sides rather than at the ends. That cuts the unsupported span
lengths in half, and the height of the far end of the rhombic isn't very critical
anyway since hopefully most of the signal has been radiated by that point.
The thing that most confounds matters is the limitation on supports to only
two, and each of them to only 14 feet in length. With 4 supports, or taller
supports, there should be no problem.
Richard Earl
All your doubts regarding the geometry of the array have gone through my
mind, and I must admit I am stymied by the limitations of the antenna
supports.
Would you concur that with a central support tie down on the 140 side
that the sag one-half of your estimate for total sag at 20 ibs tension?
I would not recommend placing the feed and terminal points at that
elevation. This would only increase the takeoff angle and nullify the
purpose of the rhombic array.
73
Rich
W9JUC
Richard Earl
After I sent the last reply I found the nomograph in the antenna book
and with a 70ft span the sag would be 2 ft.with 20 lbs tension. With 40
lbs tension it would be 12 inches.
KQ6XA
> I just thought of something... She could use a v beam and get alot of
> gain ala rhombic with less supports maybe.
A vee beam is certainly a great antenna (although not quite as good as a
rhombic). I've used vee beams before, and have had such wonderful results. I
recently fed a 10wavelength vee beam through a 9:1 balun with my AH-100 HT
running 7W on 10m, and had trans-pacific QSOs competing favorably with other
stations running considerably more power.
The use of only 3 support poles (with the highest one at the apex) certainly
makes it easier to put up than a rhombic.
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
KQ6XA
> Bonnie, about the simplest, lignhtest gain antenna you
> could come up with for the requirements given might be a 2
> or 3 element cubical quad.
That's my conclusion also so far, Dick.The gain-vs-weight and easy
adaption to rope/wire tricks makes it attractive.
73---Bonnie KQ6XA
http://www.qsl.net/kq6xa
KQ6XA
> Chances are, you will want to communicate and 10 meters will be dead.
> Which antenna will best let you fall back to 20 meters or 40 meters?
That may be the case, but I will only have a 10m.
If there was a *multiband* SSB/CW HT rig similar to the size and weight of
the Cherokee AH-100 SSB 10m HT, I would gladly take it instead. But there
is nothing out there at this time on the consumer market that I know of.
Even the Index labs or the other QRP kits are considerably larger. We are
talking minimalist backpacking at 14,000ft here, with a 50lb+ pack already
laden with camping gear.
73---Bonnie KQ6XA
Eric June
I'm going to take one more shot at your antenna problem. One of the
toughest constraints you impose is the 2 support limitation. Perhaps
there is a creative way of getting you additional supports?
Many backpackers like to use treking poles (walking sticks for the
uninitiated). I don't know how many people are in your expedition, but
how about fabricating some custom treking poles that could be telescoped
together to form additional supports once you reach the destination?
Maybe make them out of aluminum tubing, fiberglass rod, or combinations
thereof. If you could creatively come up with just two additional
supports (guyed appropriately), you could put up a rhombic.