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[mwcircle] Some interesting loop info


Rick Kunath <k9ao@...>
 

If you're referring to the LoG (Loop on Ground) antenna Tom, I can say I have built several and they really do work amazingly well. You wouldn't think so, but that antenna is something worth trying.

I built several of the LoG loops and found that the original 15-foot per side dimension was too short for what I used them for (MW, 160, 80, 40). I never tried a preamp with that 15-foot size so that might be worth doing but I didn't have one laying around. I tried longer loops and even an elevated version 3-feet off the ground but performance with noise was poor. What worked best for me was a loop on the ground 30-feet per side held in place with lawn staples (6-inch by 1-inch wide metal loops, could be made from coat hanger wire). The original was fed through a balun at the feedpoint. I was in a hurry and didn't feed mine that way. I went out searching for suitable wire and wound up getting a 500-foot spool of twisted-pair doorbell wire cheap. It's solid wire, not necessarily ideal and red and white colored, but for a test I went with it. The twisted pair was too hard to unravel into single wires, so I just paralleled the wires for the loop and then used them as twisted pair feedline all the way on the ground back to the shack. It was an all-wrong design, feedline on the ground, through the door, down the hall and to the SDR, but it worked and worked well. I've refined it since that initial test but the feedline is still on the ground to the shack and no balun at the loop. I had fed the SDRplay SDRduo through the high-impedance input initially (so no balun needed), but I have since switched to a Noelec 9:1 balun at the receiver end and feed the SMA input. That balun is modified as Roger Need described to cut the common connection between the primary and secondary windings and is much better isolated for noise. I get a very low noise floor here and good sensitivity on the loop too.

One nice side-effect of having the balun in the shack I discovered later is that I can make a resistance reading on the loop from the shack any time I need to and can determine if there is a break. I have connectored the connection points now using insulated lugs that can be unplugged, so it is easier to isolate the sections. I don't see much trouble with breakage but now and then rolling the mower over it can get the loop open. Likely that wouldn't happen with good thicker stranded wire, and I am going to redo it that way someday. The trouble is the loop refuses to die the way it is now.

I usually use two of the loops separated on opposite sides of the yard by 100 feet or so phased into the SDRduo in manual diversity mode. Both fed to the SMA inputs via Roger Need modified Noelec 9:1 baluns.

The LoG is worth trying and not really visible once you get it installed.

Rick, Kunath, K9AO