MØMCX

SG-230 feeding 60m skyloop / deltaloop

I’ve been an addict of skyloops since realising many years ago that in comparison to a dipole, you get more bang for your buck if you build a loop - certainly you get more copper in the air - and loops are resonant on EVERY harmonic so a 40m loop will be resonant on 20, 15m and 10m. A multi-band antenna for peanuts!

When I first started out with this hobby, I had a half-sized G5RV and I genuinely thought that I’d never get onto the 80 meter band. Within 18 months, I had worked out that you can build a loop of a wavelength in circumference (give or take a percent or so) and feed it directly with coax (and a balun ideally). Even better was the idea of putting loading coils in each corner of a square loop and you could lower the resonant frequency by a substantial amount.

Before getting on 80m though, I built my phase-one 40m loop which worked great and I was happy on 40, 20, 15 and 10m. A year later, I started phase-two. I cut a 6 foot section of wire out of the loop, half-way around the 40m loop as a daring experiment to give me a halo dipole for 80m! It worked:) Band-changing from 80m to 40m was a nightmare though; out to the garden, lower the loop, connect the ends (or disconnect them!) and hoist the loop back up. Ugh!

Phase three was putting up a second loop; a dedicated 80m antenna. This had 2 inch coils in each corner with 30 turns of 1mm wire and I stretched the loop around this inside of the attic to make the loop as big as I could. I estimate this was around 60m in circumference. This delivered a near 50 ohm load down at the shack via a 4:1 balun at the feedpoint.

Today was phase-four. Ditch the loading coils (and in due-course, the 2nd 40m loop) and feed the big loop with an ATU at the feedpoint and have it tune all bands from 160m upwards. With the SG-230 feeding it, 80m performs just the same - possibly slightly better because I don’t have 120 turns to worry about. 20m band seems extremly lively too.

The only fly in the ointment though is that the existing (old) 40m loop is outperforming the new loop. I’m wondering since these loops are physically nested, I may have some interaction going on? The only way to find this out is to take the original 40m loop down and suck it and see. But then I’ll have no base line to compare it to. That’s a hard one. Decisions decisions.

Looking into the distance, phase-five is feeding the loop in the garden via 450 ohm or home-brew ladder line to a big hefty manual tuner in the shack, my trusty FC-102 will come to play then. It means I can drive 10w into my Acom 2000 to deliver about 350 watts QRO. Fingers crossed.

See pics of the old 40m and 80m setups here:

• http://www.m0mcx.co.uk/gallery/index.php?/category/11
• http://www.m0mcx.co.uk/gallery/index.php?/category/15

73

Callum.

April 2nd, 2008 Posted by callum | QRO | one comment