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Author Topic: Wire Loop antenna for 40 - 20M / QRP DXCC  (Read 18481 times)

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Wire Loop antenna for 40 - 20M / QRP DXCC
« on: August 05, 2004, 12:49:31 PM »

I am at 61 entities toward QRP DXCC. I want to try another wire antenna for 40, 30 and 20M. I have a lot of experience with short hatted vertical dipoles, 88' and 44' ladder line fed doublets, half squares, slopers and the K1WA array.

BUT, I have never been able to get a loop antenna to work very well - horizontally or vertically polarized. I can only go 40' up, but 5 acres wide (hi hi). I will be using my SGC remote auto tuner and feed this antenna with ladder line.

If anyone has had really good DX luck with QRP and a loop - please let  me know what you did and what tricks you might have had to employ (feeding, open ended loops, phasing stubs, switches, etc).

OR, if you know of another antenna I might try (maybe a multiband curtain array like the bobtail or bruce array?).
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ON4MGY

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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #1 on: August 06, 2004, 11:35:44 AM »

If you're looking for antennas for the lower bands 160/80/40, you should read ON4UN's LOW BAND DXing.
A great book with all the info one may ever need on low-band antennas.

73

ON4MGY Nic
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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #2 on: August 06, 2004, 11:02:14 PM »

Thanks - I have that book and have read it almost cover to cover. What I am looking for is someones actual _personal_ experience, and with QRP.
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WB2JUF

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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #3 on: August 17, 2004, 12:51:56 AM »

I have use a horizontal loop with QRP and QRo quite successfully.  In fact it is one of the best DX antennas I've ever used.

My property does not allow me to really cut it to resonance on any one band.

Here is the setup:

Triangular in shape, supported by one tree at 45-50', another two trees at about 35-40'.  I have used the same config at only 25' feet max and it also worked great.  total wire length about 180'

I feed it with 450ohm ladder line.  That goes into a 4:1 balun outdoors near the entry point to the house.  From the balun the remaining feedline is RG-8 coax.  I use a either the internal tuner in my transceiver or my external tuner.

Results:

On 10, 12, 15 and 17 meters, it is an awesome DX antenna. I routinely break pileups with 100 watts and a tuner and can be heard quite nicely with 25 watts or less.   Here it is multiple wavelengths long and a minimum of 1/4 wave in height, and at the higher freq's, it is up to one full wave + in height.

On 20M it is an outstanding DX antenna.

On 30M it is a very effective antenna for QRP, especially since its all CW operating.  

On 40 M it is  an awesome short haul antenna (0-3500 miles) due to it's higher angle of radiation.  I routinely receive s9+20 reports on 40M.   3500 miles +, usable but you have to work at it.

On 75/80M, mediocre at best, but I can be heard.  Not quite a full wavelength on this band.    Havent tried 160.

A great all around antenna if you are willing to use a tuner.

73,
Marc, WB2JUF

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WB6BYU

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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #4 on: August 24, 2004, 07:53:44 PM »

I've used a number of different types of loops - each
have their uses.

My favorite is the horizontal loop, but that is because
I usually work 40m and often 80m and they work so well
for NVIS.  They haven't been wonderful for DX on the
higher bands because most have been around 20' high
or so:  getting them up to 40' would make a big difference.

Vertical loops don't work as well over a wide range of
frequencies, but a full wave loop can be pressed into
service on an adjacent band.  Use a diamond at the top
of a mast, or a delta (point down) shape if it is
hanging from a rope between two trees.

Bi-square:  another vertical loop, but this one is a
half wavelength on a side, and is open at the top (not
an actual loop.)  Generally built in a diamond shape
and fed at the bottom with open wire line, it gives
some gain over a standard full wave loop.

Actually you can modify a full wave loop for 20m to be
a bi-square on 10m by opening the top and adding an
open wire stub of the proper length.  It should be a
quarter wave on 20m, with the far end open (so it acts
like a short circuit.)  On 10m it will be a half wave
and will act like an open circuit.

Although a full wave loop has a bit of gain over a
dipole, I think you'll find the antenna height makes
more difference in performance than the actual antenna
shape.

For a larger beam, you can hang several wire loops
from a catenary rope and make a multi-element quad. I've
often done this for 40m on Field day, but it works on
the higher bands as well.

One of the best antennas I ever used was an NVIS design
for 40/80/160m that could be hung up vertically for
the higher bands.  Take two wavelengths of wire and
arrange them into a figure-8 or bow-tie arrangement:
this should look like two delta loops with the points
touching, and the wires cross-connected at the points.
Open one of the wires where they cross and feed with
twinlead, or coax and a 4 : 1 balun.  On the design
frequency this gives two phased loops.  On half the
frequency it looks like a folded dipole.  Above the
design frequency the pattern breaks up somewhat, but
it's still usable.

Then if you have good supports and plenty of space you
can consider a Sterba or Bruce curtain - both are based
on loops.  A Sterba is basically a half wave on a side,
while a Bruce is a quarter wave on a side.  For
horizontal polarization, a Sterba is long, while a
Bruce is tall.  I built a Bruce antenna for Field Day
one year using salvaged telephone wire and hung it off
of a fire tower in Pennsylvania, but it was absolutely
useless: all the Stateside signals were down in the mud,
and the strongest signal on the band was from Kuwait!

I've also had good luck with a bobtail curtain on 15m
with the bottoms of the tails up about 8 to 10' off the
ground.  If you have a tall tree or tower and a lot of
open space, consider a sloping Vee beam - you can
rotate it by moving the tie-off points of the wires

Beyond that your choice of antenna will depend on what
you have available for supports.

Good luck! - Dale WB6BYU

AL2I

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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #5 on: August 29, 2004, 08:44:18 PM »

I have found a lot of Loop antenna enthusiasts here in Alaska, and they seem to have excellent signals, so I am considering this myself.  I have two homebrew multiband inverted-v fan dipoles with the apex at about 65-75' at the moment, and although they get me on the air, I have discovered that the guys with the big loops in my same town can work DX that I cannot.

73,
  Dave/al2i
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W4QO

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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #6 on: September 04, 2004, 04:35:35 PM »

Rich,

I use an 80 M loop on all bands but seems to be the best on 20M.  It is a full wave length at about 40 feet.  In the WPX contest at QRP levels, I worked about 350 QSOs in 60 countries in about 15 hours.  I find it really works good domestic on 20 as well such as Sweepstakes.  On 40, I don't always "get my man" on first call but 20 it's usually first call.

Jim W4QO

PS if you like QRP, why not join us in QRP ARCI - www.qrparci.org  Great mag and lots of stuff among QRPers!
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WIRELESS

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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #7 on: September 10, 2004, 08:35:38 PM »

Why do you dislike beams?  You seem to have tried every antenna except a yagi.  When picking an antenna one should resist judging it by specs.

I use a small homemade 2 element beam portable on a 20 ft. high mask and it works much better than someone might guess by just looking at it.

There is more to a beam than raw gain.  Try one and you may like it.  If I had 5 acres, I would have all beams except for 160 and 75.
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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #8 on: September 19, 2004, 01:18:13 PM »

I actually have had a tower and yagi in the past and have also built a Moxon rectangle - which is also a beam. Towers, beams and quads are excellent - one day I might go back to them. It just seemed to "easy" to buy the tower, beam and amplifier - I wanted more of a challenge and all while getting an education on gain, pattern, TO angle, high and low angle noise and propagation.

My goal has been to try just about every wire antenna possible just for the fun of it, and achieve all my DXCC goals this way. I am almost there, and it has been fun.

So far, the best wire antenna that I have tried is the K1WA array - monoband on 20M. It combines some of the characteristics of the K9AY receiving loops that I have used on 80 and 160 (switchable cardiod pattern - albeit noisier than the K9AY), and the low takeoff angle of a short hatted vertical dipole.

Thanks for all of the personal experiences - I will try a few of these.
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WU7X

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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #9 on: September 23, 2004, 02:41:42 PM »

A the bottom of the past solar cycle, I was using a full wavelength rectangular loop on 40 meters.  It was horizontally polarized with the top wire about 50-55 feet off the ground.  My best Dx on grayline one early spring morning was Amsterdam Island in the South Indian Ocean.  I live in the Pacific NW, so that was geographically about as far from my qth as one could get.

I recently reviewed some of Cebik's modelling data on his website.  It shows that a wire doublet will do a little better than that quad, about one dB or so.  My practical experience from my location seems to disprove that.

I presently have a 40 meter doublet and a Radio Works 80 windom beam up.  Both at 50 feet or less.  Neither one seems to hear or work 'em as well as that quad.  I will be converting the doublet into a quad sometime this coming month.

Good luck, and let us know what you decide to go with.

Dale WU7X
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KO4NX

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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #10 on: October 01, 2004, 09:22:18 AM »

Hello:

I currently use two full wave quad loops on 20/40 meters with my Elecraft K2.  I was able to “nestle” the 20 meter loop inside of the larger 40 meter loop thereby saving considerable space on my property for other antennas.

I positioned my loops to favor Europe and New Zealand. I found that I can work almost all European Countries and the Pacific, with little effort, running five watts from Virginia. Last weekend I operated the CQWW RTTY Contest using nothing but wire loops and 150 watts.  Preliminary scoring from contest.com indicates I placed around fourth in North America.

Feeding the loops properly is the trick for broad band resonance. I use a 1/4 wavelength matching stub of 75 ohm cable (RG-11). From the matching stub one should use 50 ohm cable to the transceiver, or transmatch (A tuner is almost never needed). There are some commercial vendors that sell 2:1 baluns for this application, but I have found these to be cumbersome and require additional support for the antenna system.  

The best way I have found for cutting 1/4 wavelength matching stubs, is to calculate 1/4 wavelength for the frequency of interest (Don’t forget to add in velocity factor) and then cut the coax slightly long. Once this has been accomplished, prepare one of the cable ends for installation of a PL-259 UHF Connector. Take the exposed center conductor of the matching stub and couple a 50 ohm resistor in series with the conductor. Next, connect the opposite side of the resistor to an antenna analyzer (i.e. MFJ-269, or equivalent). Finally, set the analyzer to the frequency of interest and begin trimming small sections of the matching stub until resonance.

Both of these loops are broad banded. I have found that the SWR is less than 2:1:1 across a majority of 40 meters. In the case of 20 meters; I do not require the transmatch until the very upper portion of the sideband segment. One additional benefit of the 40 meter full wave loop is that it works nicely on 15 meters as well. In my case, I have an excellent match right around the C.W./Digital portion of 21 MHZ with some bandwidth to boot! I have had no problems using the 40 meter loop on 15 meters with regards to working DX or contesting with low power.  

So there you have it, my two cents, I hope it helps. If you have any further questions please do not hesitate to ask.

73 & GL

KO4NX
Rich Miller
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W9OY

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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #11 on: October 05, 2004, 08:32:15 AM »

Do you feed each loop with a seperate feedline or are they common?  Where do you feed the loop corner, middle of a leg some percentage of a leg?  

Tnx

W9OY
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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #12 on: October 05, 2004, 08:35:10 AM »

I studied and modelled quite a few loops and arrays. I just didn't have enough supports in the right place and height for a horizontal loop.

This past weekend I put up a 4 element Bruce Array. The main reason with going with the Bruce is that I get at least 5 dbi gain on 40M with a low TO angle, and it takes up the same space as a G5RV. The pattern and TO angle scaled all the way from 160 - 10M, and gain increases significantly in the higher bands without developing the nasty high angle lobes that make a good low band antenna bad on the higher bands.

The antenna is cut for 40M (4 phased 1/4 w.l verticals and 280' of wire) and I have bottom center fed it with an SGC 230 remote autotuner and a 1/4 w.l counterpoise. This is documented in the latest ARRL antenna book.

The antenna has just about the best S/N ratio I have experienced with a wire antenna. I seem to be able to hear weak signals much better than a single element wire antenna - and the past couple of days have been pretty noisy, with the A up higher than 10.

It works very well on 80M - 10M as I have worked good DX on every band except 10M. It will take the rest of season to see if it is the "killer" antenna I think it is.

Take a look at this antenna in EZNec - I think this antenna and my K1WA array will end up being "it" for a long time. (But I always say that - hi hi).
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KO4NX

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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #13 on: October 05, 2004, 09:30:52 AM »

Hello:

I feed each loop separate. In my case, I take each of the matching stubs and plug them into a remote coax switch. From the coax switch I use 50 ohm coaxial cable to my transceiver.

As for the feed point of the 20 and 40 meter antenna, I have found feeding them on the bottom corner to work best. Make sure that the center conductor of the feed line is coupled to the vertical element, and the braid is hooked to the horizontal element of the quad loop. I have used this feeding technique with quad loops that have a bottom horizontal element as low as 6 – 8 feet from the ground. Of course it works just as good, if not better, with more altitude (15 – 30 Feet AGL).

It should be noted that in the case of my 80 meter full wave delta loop, I found it best to feed the antenna at the top corner. The reason for doing this is due to the fact the feed point impedance was still too high at low feed point altitudes. By raising the feed point higher above ground, I found the impedance would drop.  Finally, at about 70 feet, I was able to get a 1:1:1 match in the DX portion of 75 meters (my target area). Keep in mind that the bandwidth you see at higher frequencies will decrease at lower frequencies such as 75 meters. In this case if I wonder too far out side the DX window a tuner is required.

I hope this helps.


73 & GL

Rich Miller
KO4NX


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WR8D

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Wire Loop antenna for 40 - 20M / QRP DXCC
« Reply #14 on: October 11, 2004, 10:37:05 AM »

270 feet of number 12 put up in a triangle shape. 35 feet off the ground fed with 450 ohm wire "any length" to a 4:1 centaur balun. From the balun a short run of rg-8 to the antenna tuner. I use 213 for that. Outstanding on 80-10 meters. I have put up dipoles cut for individual bands and the loop always was stronger and out performed the dipole which was cut to each band with a low swr at each freq it was tried on. This loop is  intended to always be used with an antenna tuner so don't ever worry about the high swr you will see if you check it direct. I have stopped experimenting with antennas now since the horizontal loop out performs anything i ever put in the air. I did one other thing to this antenna i made my feedline. Its spaced 6 inches apart and made from number 12 also. It can rain cats and dogs and the swr never moves because of the wide spacing. There is no skin effect like the smaller 450 has in bad wx. Also spaced 6 inches apart makes it 600 ohms which the antenna likes even better. I have friends that are running this same configuration at 20ft and it honestly really "smokes". Take the time to put it in the air and you'll really be amazed.
73
John WR8D
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