Hi Jim et al:
How about a dual band inverted L? A rope over a tree will hold up the
wire. Anything from 40 ft vertical and up will work OK on 160.
A trap at about 66 feet out works fine for 80. I made one from about
13 turns of 3 inch diameter, 4 turns per inch, coil stock with a couple
of 85 pf door knob caps to tune it. You can adjust the L-C ratio to
what ever capacitors you have, as long as you get trap resonance near
3520. One note: I have had too many single cap traps blow on 80, so I
always use a pair of 75, 85, or 100 pfd door knobs in parallel, in lieu
of a singl 150 or 200 pf door knob. Spray the trap with clear sealant
like Krylon to protect from salt air and rain.
The inductance from the trap shortens the length of the L on 160 from
about 128 to 115 feet.
Take as much radial wire as you can and put it out. We used random
lengths at one site, and it worked well. We had anywhere from 30 to 80
feet long radials, maybe 40 or 50 total. Lance Johnson will tell you
his ground plane plate is ideal. Any piece of aluminum plate with SS
machine screws for radial connections will do. We use a dog tether
(looks like a large cork screw) thru a hole in the middle to hold it
down and anchor the feed point.
On 80 the feed point should be close enuf to 50 ohms. On 160 the feed
point will be lower impedance. Either use an UnUn or take an L network
like the Tentec's or the Collins 180 styles with outboard extra shunt
caps for 160 match, and a series roller inductor. You may need 2500
shunt capacity to match on 160 with anywhere from 1 - 10 uhy series
inductance depending on the feed line length. We used RG8X which works
fine at a KW on 160 and 80.
You could also make a three bander with a 40 meter trap at 33 feet or
so! We have made them. Jeff, K1ZM, has a nice design too, but a bit
stout! He uses RG8 or RG213 to make the traps!
Good luck, 73 George K8GG
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