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wire size - QRO horizontal loop

Oct 30th 2011, 10:13

K7NSW

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I live on an acre contained by a fence. I plan to run a single continuous wire all around the acre along the fence for a low noise level hf receiving antenna. My 45 foot tall GAP vertical is noisy as are all verticals. Using stranded copper house wire. Will feed the loop with ladder line from a tuner. Loop will be 6 feet high 685 feet around hung on ceramic insulators every 8 feet. I might want to transmit with it. Transceiver is 100 watts. My hf amplifier is capable of 1300 watts: a pair of 3-500Z tubes. What size wire? #14 or #12?
Oct 30th 2011, 13:11

gw0nvn

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Hi,

I use a hf wire loop antenna myself. It runs very close to the boundary of my property. Aprox 140ft all the way around. In my case it is 40ft above the ground. For me its a good compomise antenna in my circumstances for both transmit and receive from 80m-10m. For 20m-10m I can use other antennas.

As it is used for transmit the antenna has to be a safe distance from the public ( known as an uncontrolled enviroment) and posible sources of emc problems. All Regulators (FCC, Ofcom etc) have rules on this. See the ARRL web site.

So to answer your question. It is always best to use the wire which has the least resistance per foot length., can handle the current with the heating effects and is mechanically strong enough to survive.

However I would suggest you may be asking the wrong questions. You have a large area to play with and you have a noise problem. Also is the antenna for local contacts or DX?

. There is plenty of information on the ARRL website on how to track down the noise and how to deal with it. You may find that there is a local electrical noise source (fizzing insulators on overhead power lines). The Power Company can sort these

For horizontal loop antennas or sky hooks as they have been described as 'A Balanced, Everyday Approach to All-Band Bliss' by NT0Z on the ARRL website or on any search engine decribes how to build one and a suitable atu.

With a loop antenna as described because of its height of 6ft above the ground on most of the hf bands it will act as an NVIS antenna. Good for local contacts but dificult for dx as most of the rf is being radiated straight upwards. As mentionned there is also FCC regulations dealing with RF safety including Radhaz and rf burns if someone touches the antenna. Again there is information on this on the ARRL and FCC websites

Try the antenna on receive anyway but for transmit you will need to have it at a height that is safe and used within the regulations. If you can get it up to at least 40 ft it will work well.

All the best

Oct 31st 2011, 12:44

K7NSW

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
gw0nvn: thank you for your thoughts. I agree with you as to the safety issue. The antenna will be used as a receiving antenna. I was reading about long wire antennas and loops. I like the idea of lots of wire down low for a low noise antenna. I will feed it with window line via an L tuner I bought from Ten-Tec. I am thinking I will have a better chance of getting a good match to my receiver than if I end feed a random length wire. It seems that a closed loop fed in this fashion is a balanced antenna. I prefer that also. Do you think I am correct in prefering the loop to the random wire? I cannot get a longer run than 680 feet around a square and I am not looking for directivity or gain. So I am not looking for the performance of a beverage.
Nov 1st 2011, 23:42

gw0nvn

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
hi,

Unfortunately I lost my reply in my PC. So i'll re write it and cut and paste it in.

In the meantime have a look at http://www.standpipe.com/w2bri/ which is a good site for magnetic loop design. Just feed it with a loop of about 1/5 of the circumfrence. have a look at Shielded Loops for receive and the SGS website wich describes some stealth wire loop designs.

Simon GW0NVN N1XIH
Nov 3rd 2011, 00:18

gw0nvn

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Hi,


Providing your boundary fence is wood and not metal there should be no problem in ‘tacking’ the wire near the top of the fence on your side. Feeding it with balance feeder to a balanced ATU will give you a quick and simple antenna system. Providing you use low power, about 10-20 W it will give you an additional transmit antenna. If you have the wire already at hand this is a quick and easy project. Mult stranded plastic coated wire is fine. As always the thicker and less lossy the better.

If you only want an antenna for receive you do not need such a large loop. Your portable shortwave receiver uses a very small whip antenna. Yet in many cases it receives the same stations that your GAP Vertical will. The reason is that the frontend selectivity and gain is enough overcome the antenna losses and the noise throughout most of the hf bands. Your GAP vertical is however much more efficient especially on transmit compared with the 2ft whip antenna.

In this case a Shielded Loop Antenna is good. This is normally made from semi air spaced or foam dialectric coax cable. For this you only need about 20ft of coax for a loop to work on 160m. This is fed by coax to the shack. These are not very efficient antennas and some times need an amplifier to bring the signals up to a level for the receiver. With new ham transceivers all you may need to do it switch in the fontend amplifier or switch out any attenuators and turn up the rf gain control. It does have directional properties so you could build two and tack them to two of your boundary fences at 90 degrees.

If you want an antenna for transmit I would recommend a Magnetic Loop. I have used them both outside and in buildings where there is much noise and QRM from modern living. The size of the loop is much less than ¼ wavelength. Normally 1/10 wavelength. I use a 1m per side loop which I tune from 40m – 12m. I feed it with another loop of 1/20 the circumference of the loop. For 80-160m a loop of about 7ft per side would work. The URL details also has a calculation program to help you chose the optimum size of loop.

I have also used a wire loop successfully on 80m and 40m for QRP psk31 contacts around Europe. This consisted of a horizontal oblong shaped loop 16ft on the long sides and 4ft on the short sides. Suspended from the ceiling in my small bedroom. It was fed with balanced feeder via a home brew matching unit.

Below are some good websites. But the ARRL has much information and articles.

Wire loop Antennas
http://www.hamuniverse.com/kl7jrloopnotes.html
http://www.hamuniverse.com/kl7jr80loop.html
Shielded Loop Antennas
http://www.n6rk.com/loopantennas/pacificon.pdf
http://www.frontiernet.net/~jadale/Loop.htm
Magnetic Loop Antennas
http://www.standpipe.com/w2bri/
http://www.k4sx.com/slot%20antenna.htm
Other antennas
http://hem.passagen.se/sm0dtk/
http://www.k4sx.com/slot%20antenna.htm

Simon GW0NVN N1XIH

Nov 3rd 2011, 23:27

K7NSW

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Thank you. The effort you put into your reply to me is impressive. I will do some reading. Unfortunately, my fence is chain link. I doubt that I will transmit on it. I am hoping it might be a good listener. As in all things amateur, I put it up and see how it works. So also with this. Thanks again.
Nov 4th 2011, 01:47

gw0nvn

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Hi,

Thanks for your comments. You can see why I was not happy when I pressed the wrong button and moved off the Forum web page.

Definitely try it. Load up the fence. You may find that you have to bond some of the sections together if you hear noise bursts or scraping sounds. Some braid or thick wire and jublee clips should do it. I coupled up a metal bed as an antenna once and have also used insulated wire layed on the ground for both transmitting and receiving.

Looking for info on the FT950 I came across this which is another receiving loop. But for 160, 80 and 40m.

www.ac0c.com/main/page_antennas__homebrew_1608040m_rx_loop.html

Anyway have fun. If you are in the HF SSB Sweepstakes on the 19th and 20th November I'll be portable in Utah as N1XIH/7 using an FT817. Its an enjoyable contest and I hope to add an extra two antennas to my set up. Providing I get enough time to build and set them up on site.

Simon GW0NVN N1XIH

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