20m loop pointers

You are welcome any time, Alex. Just sorry I missed the first post (although I have missed a few lately).

If you have a general-coverage receiver, or even a spectrum analyser that can measure 14MHz, then you can scan the band without a capacitor at all; just twist the insulated ends of the coil (without shorting) about 5 twists.

Tune the band for maximum noise. The bandwidth will be about 60kHz or more for noise (but the VSWR will be bad for more than about 20kHz).

Alternatively, if you have a GDO then you can put two turns loosely around the GDO coil, and connect them to the feed loop. You should get a really massive dip. To measure the exact frequency with the GDO then move the two-turn loop away from the GDO so that you get a weak dip, then measure the frequency of the GDO.

If you want to be really posh, then capacitively couple a lambda-diode, a tunnel-diode, or any other negative-resistance device, across the feed-loop and measure the frequency of oscillation that is radiated from the antenna.

BR Harry

Hi Harry!
Thanks for the reply, and getting back to me so quickly! I will definitely have a re-measure. I think part of the issue might be where I have placed the capacitor, and weather the feeds from the capacitor to the ends of the loop might be lengthening the wire. Will have a n experiment and see what comes out. Hope you're doing well. Thanks for the excellent website.

Best

Alex

Hi Alex,
Sorry, but I didn't see this post, but then again I have been off-line for a while due to personal reasons.

If you have the loop exactly the same size as I wrote in the article, then it matters not one iota what material you use for the support, as long as it is not conductive.

Assuming your coil and feed-öoop are the correct size, then a poor VSWR means that the loop is not correctly tuned. The tuning capacitor must be adkusted to give resonance. If not then there will be a very high VSWR and an efficiency less than 98% that of a dummy load.

If you use a small (5-50pf) capacitor then you will hear a noise rise when the capacitor is tuned through resonance. But note that without the capacitor the antenna will resonate at about 15MHz, or so - just slightly above the 20m band.

If you have used a little too much wire, or the coil is too big, then resonance will be below 20m and you will never get a resonance.

So please check your measurements.
Check for close metal objects.
Check for resonance with a variable capacitor.

Note that a small variable will burn if you try to transmit into it. For transmitting you need an high-voltage capacitor, as documented on my homepages.

BR Harry - EA/SM0VPO

Hi all!
Thought I posted this already, but cannot find it at all, so apologies if it appears again.

I've had a go at building the 20m loop antenna, but with wooden broomsticks rather than pvc pipe.

I think I have done everything correctly, but the swr is pretty bad...

Does anyone else who's built one have a my pointers for a novice (common mistakes, simple tweaks etc)?

Any help to get active and back on my favourite band would be super-appreciated!

Best,

2E0AZU