HF full wave loop..opinions please!

[5thElement]

I'm thinking about trying a full wave loop this weekend but im not sure what would be best to try..

My options are either in the loft or outdoors at 6-7ft off the ground.

Outdoors it would be in a slightly awkward shape so im not sure how much that would affect it - it would also be pinned to the top of the fence and have to run along some plastic guttering which isn't really ideal!

Would look like this..



In the loft i should be able to get it fairly square but having the sides raised if that makes sense? i'd be running the wire up the beams at 2 ends to maximise the wire length i can use.

Both would be 20m wires..

Thoughts?

[26CAB40]

Low down outside would be my preferred of the two.
High angle radiation on 80m and 40m, low angle on 20m and above.

Best fed with 400 or 600 open feeder or a 4:1 balun to desktop ATU, if you can use an SGC tuner at the feedpoint even better.

There will be more absorption in the loft plus the chance of coupling into the house wiring.

The kinks and bends you show in the diagram will have little effect, only a narrowing of the shape or parasitic wires would
have any major effect otherwise.

I made one out of a spare reel of crappy RG58, I lay it on the roof tiles, fed in one corner by a cheap balun.
It went along the front of the house to the end of the semi where next door started, up the roof, over the apex, back down, along the rear edge of the roof, back up and
over the apex again and down to the feedpoint.

Steve G3TXQ kindly modelled it for me, not a bad little antenna, once fed with my SGC-231 it worked a treat from 80m to 10m.
The loop was not overly affected by lying on the roof tiles even when wet with rain.
No TVI and very low noise.
No real gain to speak of but the neighbours didn't even know I had an antenna up.

[5thElement]

Thanks for the input, much appreciated.

I'll be feeding it with coax via a 4:1 balun and i can tune it with the LDG Z-100 atu.

Fairly certain im going to try it outdoors on the fence - i love the idea of yours actually - decent size and pretty stealthy.

My other concern is that it might be slightly longer than 20m so it might not end up quite resonant where i wanted it so i'd need to rely on the atu in that scanario.

From what i've read the general opinion is that loops seem quieter compared to verticals etc so im looking forward to seeing how it compares to the 1/4 wave wire vertical for 20m i'm using at the moment and also running WSPR for a couple of days to compare the results.

Definitely worth a try - i've tried nearly everything i can that will fit into the garden but i've never used a loop before but it sounds ideal - cheap to build, easy to put up, nearly invisible and so on.

Will post my results if i get it setup tomorrow.

[crusty]

Not much low-angle radiation on 20m at 7ft above ground.

[26CAB40]

Well, as low as you can get at that height.
To be honest it would need to be fairly high up to equal a vertical in that respect, but it better than firing straight up.
Mine was at roof height and achieved some excellent results on 20m/17m.

[5thElement]

Got this up this afternoon and ended up using about 28-30m of wire to create the loop, mostly running along the fence tops about 6-7ft off the ground, one part around a shed, another through some bush/tree and some runs along plastic guttering - not exactly ideal conditions!

Here's how the final shape ended up (in green)



I'm feeding it through a 4:1 balun and these are the results of a quick test of the swr on a few bands.

3.800mhz - 7:1
7.100mhz - 3:1
10.145mhz - 4.5:1
14.000mhz - 1.8:1, 14.200mhz - 2:1
28.500mhz - 2:1

I thought the reading for 30m was odd as i used roughly 30m of wire which would make a full wave on 30m. I've only tried tuning 40m with the ldg z-100 so far and it tuned up fine - i reckon i could do with a manual atu though to tweak it a bit more - i'll have to put one on my radio want list!

I left WSPR running on 20m for a few hours using 5w and here's a map of the results - a few in the US, one in Venezuela which is a new one to me and a load in Europe so it looks quite promising at the moment.



I'll report back when i get round to testing it more.

[26CAB40]

Not bad for a bit of low wire eh.
If you can, get an SGC coupler, they are a revelation with loop antennas.
The whole business with baluns, co-ax and desk-bound tuners will never
offer you what an SGC can.

[northern35s]

I thought the reading for 30m was odd as i used roughly 30m of wire which would make a full wave on 30m.

What is the antenna fed with? don't forget you have a 4:1 balun in line, which, as I'm sure you are aware, is an impedance transformer, a full wave antenna should theoretically have a 100Ω impedance (dependent on length, velocity factor, loss etc), but you'd probably need to use an analyser to find this out for your installation.

Edit to add: It looks like it's working quite well, now lets see if you can work Stateside with voice

[crusty]

I thought the reading for 30m was odd as i used roughly 30m of wire which would make a full wave on 30m.

You'll find the wire length for a resonant full wave rectangular(ish) loop is significantly shorter than the standard loop antenna calculation of L (ft) = 1005/f (MHz). This may account for the readings you're getting on 30m.

[m3pog]

Got this up this afternoon and ended up using about 28-30m of wire to create the loop, mostly running along the fence tops about 6-7ft off the ground, one part around a shed, another through some bush/tree and some runs along plastic guttering - not exactly ideal conditions!

Here's how the final shape ended up (in green)



I'm feeding it through a 4:1 balun and these are the results of a quick test of the swr on a few bands.

3.800mhz - 7:1
7.100mhz - 3:1
10.145mhz - 4.5:1
14.000mhz - 1.8:1, 14.200mhz - 2:1
28.500mhz - 2:1

I thought the reading for 30m was odd as i used roughly 30m of wire which would make a full wave on 30m. I've only tried tuning 40m with the ldg z-100 so far and it tuned up fine - i reckon i could do with a manual atu though to tweak it a bit more - i'll have to put one on my radio want list!

I left WSPR running on 20m for a few hours using 5w and here's a map of the results - a few in the US, one in Venezuela which is a new one to me and a load in Europe so it looks quite promising at the moment.



I'll report back when i get round to testing it more.

You've cracked it. Well done lol

[crusty]

[5thElement]

Nice to see your call in the spot list m8! i wonder what antenna your running on 20m now?

I've left WSPR running (still 5w) and the antenna seems to be performing okay, i've been quite surprised by the number of spots in the US considering the low height of the antenna and what i presume must be a pretty high take off angle compared to a vertical?

Got spotted by another Venezuelan station also.

The 3Y4 station was spotted by me - can't find any info on the station though on qrz/google so im not sure about that one - first time ive come across the prefix too.

Here's the map now for the last 24hrs on 20m.

[m3pog]

Yeah good to see your spot too mate

3Y Bouvet Is (ITU Zone 67 CQ Zone 38)
3Y Peter Is (ITU Zone 72 CQ Zone 12)

Though neither of those places correspond where your spot is shown on the map!

http://maps.google.co.uk/maps?f=q&sourc ... 753418&z=6

http://maps.google.co.uk/maps?f=q&sourc ... 08647&z=12

3Y4 eh... hmmmm. You've got me there



Just got the cobwebb up at the moment, would like to get back on the lower bands
but with this pea sized back garden I havnt got a hope in hell of getting anything half decent up.
So I'll stick with this for now. Seems to be working well and fits snug on the back of the house with a pair of T&K's

Definitely seems to be doing the business for you, so if it works, don't question it!
I heard you through HB9HD a few weeks ago on 10m, but it was getting late and the repeater was past its best.
There where a couple of local lads as well as you through the box.
Tried to get you on the input, but it was a scrum with the locals here!

[26TM642]

Wow, not bad for 5W. Whats the receive like?

I've got a SGC230 antenna coupler sat here doing nowt since I bought it. Your post has given me some motivation to put some wire up this weekend and get the thing going.

[5thElement]

Yeah good to see your spot too mate

3Y Bouvet Is (ITU Zone 67 CQ Zone 38)
3Y Peter Is (ITU Zone 72 CQ Zone 12)

Though neither of those places correspond where your spot is shown on the map!

Yeah, i knew something was odd with it, probably someone messing around or maybe a genuine mistake, but i doubt it! cheers for pointing out the geographical error, i never got round to looking it up properly myself.

Just got the cobwebb up at the moment, would like to get back on the lower bands but with this pea sized back garden I havnt got a hope in hell of getting anything half decent up. So I'll stick with this for now. Seems to be working well and fits snug on the back of the house with a pair of T&K's

I heard you through HB9HD a few weeks ago on 10m, but it was getting late and the repeater was past its best. There where a couple of local lads as well as you through the box. Tried to get you on the input, but it was a scrum with the locals here!

Was thinking about building a cobwebb myself actually - it must stand out like a sore thumb though looking like a washing line 30ft in the air lol from what i've read they seem to perform quite well though. Is yours commercially built or homebrewed?

Cheers for your email about HB9HD, i totally forget to reply as i rarely check my hotmail addy these days so apologies about that. It was quite funny actually as at one point the repeater was practically being hogged by hams in Liverpool and the surrounding area lol the signal was pretty up and down with me also and it was the first time i've actually heard 10m FM activity so it was cool to be able to work it for a couple minutes - was quite surprised when my callsign was acknowledged - i think i was using the 20m vertical at the time (5m wire taped up the side of a fishing pole lol) tuned to 10m.

Wow, not bad for 5W. Whats the receive like?

I've got a SGC230 antenna coupler sat here doing nowt since I bought it. Your post has given me some motivation to put some wire up this weekend and get the thing going.

Receive is a big grey area for me unfortunately - at times i can have S9 noise over most of the bands and at other times i can turn the rig on and the noise levels are pretty much S0-S1 (typically early in the morning when im in bed or getting ready to leave for work! whenever i actually want to use it, sods law states the noise levels will be too high!)

I'll need to give it a better test over the weekend as last weekend there was a contest running so the chances of any meaningful reports was zilch lol luckily noise levels were low for a while and i heard hundreds of stations so the antenna certainly seemed to be doing the job and i was quite pleased with it on 40m aswell, pulling in plenty strong signals from the UK and Europe.

I have noticed a big increase in US stations received on WSPR, whether this is due to propagation or the antenna remains to be seen, but it certainly looks promising - i'll need to sit down and compare received signals from the same days last week compared to the same days this week - how meaningful that is im not sure as propagation changes but it should give me some indication? could be that the noise levels are lower on this antenna therefore it can pickout weaker signals.

I'd have been happier knowing the loop was actually a full wave on a certain band, but it would have been awkward to fit a specific length of wire in so decided to just string up as long a piece that would fit and use the tuner but swr on 20m and 40m are alot lower than i expected.

Go for it and get one up yourself, if it fails it's only cost you a few pennys worth of wire which you probably have lying around anyway.