I've spent several days experimenting with various loop designs, and this is what I ended up with:






The loop is about 24" diameter and is made from 10mm copper; I soldered it to a pair of PL259s and plugged into So239s so that I could easily experiment with alternative loops.

You could just as easily use flat aluminium strip - here's one I did that way:


I tried various amplifier circuits - including one with very complex hex-filar wound transformers and claimed very high performance - but I ended up with the simple circuit here:
http://www.qsl.net/m0ayf/active-loop-re ... tenna.html

I used a pair of 2N3553 transistors which I had to hand and which are probably "overkill" - but they are robust (UHF 7W) and it turns out they are quite linear. I added the relay protection that he shows on the schematic and controlled it via the external T/R line on my transceiver:


It makes a real nice antenna for general listening on my HF225. I found that putting it outside just a few tens of feet from the shack drops the noise levels considerably. It seems pretty sensitive from MW thru 20m.

I also experimented with the varactor-tuned loop here:
http://www.n6rk.com/loopantennas/NCJ_lo ... a_N6RK.pdf

Coverage is limited to 160m and 80m, but if I was serious about low band DXing, that's probably the one I would go for.

73,
Steve G3TXQ

Very tidy build Steve, I might try the flat strip version as I have a mountain of the stuff.

Nice loop Steve like the construction and it should be simple to reciprocate between the circuit diagram and your pictures it gives all the build information needed
For those with major noise problems even after trying the loop, Martin G3JNJ site has some links to noise canceller circuits
http://g8jnj.webs.com/rfnoisecancellation.htm
the Chris Trask Noise Canceller Design looks good, might give it a go myself hope the link is of use to some others on here.

Peter GM1CMF

Now that I like....

As you have said before, we are noise-limited on the LFs.

As we are entering the golden age of electrical QRM, all we need is the Wellbroke loop upped to 80 and 40, G1HBF's homebru noise phaser-outer, and an anti - i.e. noise no signal - antenna. Plus maybe an Rx/Tx box.

Then we can all sit there sniggering like Muttley

It covers 0.5MHz to 18 MHz as it is now

73,
Steve G3TXQ

Every loft should have one.

You clever clever man. Thank You.

Can you now use your wisdom to design us the worst antenna ever built?

One that will pick up every single crackle of electrical shoite within miles, but no signal whatsoever....

I like the PL259 option. Means it can be assembled the other side of the attic door. Nice kit. I might make one to test against the Wellbrook

Stop it Steve , i have enough to do on other projects, but this is on the list of things to do.

Nice job, well done

Keith G0TSH

Nice work Steve. Does yours show directionality as the Wellbrooks do? I guess it has to being a loop.

Are you using it for diversity? I've been toying with that idea but will wait to see how I feel once my inverted L is fully commissioned. Which would be soon if it ever stops raining.

David
G4YVM

Too late, step forth the Q-Tek Penetrator

I see broadside nulls approximately 20dB - 30dB deep, depending on frequency



Nope - this was just a bit of experimenting on a couple of wet afternoons It seems to work nicely as a low-noise receive antenna on 160m, 80m & 40m into the separate Rx input of my TT Corsair. It's also very handy coupled up to my HF225 for GP listening - no need to swap antennas etc.

73,
Steve G3TXQ

Don't know how I missed this but thanks Steve for taking the time so that some lazy toad like myself can actually build something knowing that it will work.

Cheers, Dave.

Hi Steve.
Just a couple of quick questions.

1. Would it make a big difference performance-wise to build it as a square instead of a circle?

2. Do you know if someone makes an amplifier kit that can be used with this type of antenna?


73 de LA3AKA, Johnny

I suppose the elephant in the room is "how does it actually compare to the commercial Wellbrook version?". If one buys a Wellbrook one onbviously gets a lot for the money, or atb least I think it seems that way as a potential future customer, but does one get THAT much more for the money that Steve has got for little money?

David