Sunday, July 22, 2012

Simple Antennas for the Amateur Radio Operator--a continuing series

KH6JRM's Amateur Radio Blog

Post #172

A homebrew 20-meter loop

For the better part of two days (Saturday and Sunday), conditions on 20-meters from the Laupahoehoe qth have been poor.  Apparently, a near class X solar flare from our sun has made severe inroads on HF propagation.  So, once my xyl and yours truly finished our daily routines, I decided to work on my modest "antenna farm" in the backyard.

Although my hastily-built 20-meter delta loop worked fine, it was low enough to cause problems with neighborhood pets, wild pigs (we have many here), assorted birds, and other furry creatures (feral cats, goats, and even a lost cow or two).  Living in an agriculture zone does present certain problems.

I took down the delta loop and looked around for an alternative location--not an easy task on a small lot.  While I was creating my replacement antenna scheme, I glanced at my wooden garage.  It measured 17-feet by 16-feet, if I included the laundry room.  Aha! Why not draft the wooden panels beneath the roof for an antenna support?  The roof was 10-feet above ground level--not ideal, but it could work.  I measured and cut a loop of 66-feet for the antenna, using AWG #22 gauge hookup wire I found in my junk box.  At 66-feet, the loop would be about 3-feet short according to formulas found in several antenna books.  However, my Drake MN-4 would be up to the task if I used 450-ohm ladder line and a 4:1 balun. 

After I tacked the loop onto the roof boards of the garage, I ran 20-feet of ladder line to the balun and then used 10-feet of RG-6 coax to connect the MN-4.  Three feet of RG-6 cable attached the system to the Swan MX-100.  I used RG-6 (with suitable connectors), because that's what I had on hand.  Wonder of wonders, the loop worked.  The swr is a little high on the lower portion of the band (antenna is a bit short), but the SSB part of the band can be managed nicely.  I expect to add 3-feet of wire to the loop so I can reach the bottom portion of the band without creating distress for the Drake MN-4.  Under the current configuration, the tuner doesn't get hot or arc-over.  Presently, I running about 20-watts output on SSB and CW.

Best of all, the loop is invisible to passers by.  I can use the loop on 20, 15, and 10 meters.  Like my other loop (the full-wave 40-meter loop under the house), the antenna is quiet and unobtrusive.  So far, I've made only local contacts in Hawaii.  Once conditions improve, I'll give the antenna a few more tests.  This is not an ideal antenna, but it works and blends it the environment.

The 40-meter inverted vee along the mountain side of the qth continues to perform well.  The antenna is presently nested to the ground because of a few thunderstorms last night.

Until next time,

Aloha es 73 de KH6JRM--BK29jx15