Scott, N4JN wrote:
"I do have a couple of trees that will give me the 50-60 vertical feet
and 100 or so horizontal feet that I need to string it (an inverted L).
Is there a formula for figuring the length or is "in the ballpark"
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For direct series feed (with no capacitor), I'd make the total wire
length 1/4 wave long (~130 feet).
==========
"I have acquired a ~600-1800 pF variable cap of the air-dielectric
variety (refugee from an old tuner I think) which doesn't have much
plate-plate spacing but I think that it'll work."
----------
You can raise the base feedpoint Z of the antenna if you make it longer
than 1/4 wave. ~55 feet vertical and ~140 horizontal with the inductive
reactance tuned out with a series capacitor of about 100pF will yield a
close match to 50 Ohm coax, assuming a ground system with no loss.
With the small ground system you plan, I'd use just a 1/4-wave inverted
L, without a series capacitor. With the ground resistance of a small
radial system included, you'll probably be close to a 1:1 SWR feeding the
antenna directly with 50 Ohm coax.
==========
"I hope to feed it with some RG-58-type coax as that is the only run I
have that is long enough to get from the shack to the antenna feedpoint
tree. Will this type of coax be OK?"
----------
RG-58 will easily handle 100 watts on 160m. Loss would be negligible for
a run of 100 feet, as you plan.
==========
"Is 12 AWG solid sufficient? Would bare copper be better? What about
the radials? Does insulated wire work OK in this role? I can
realistically only get two or three 1/4 wave radials in the ground. I
might be able to get a few more 1/10 wave wires in the ground. Advice?"
----------
For the antenna, I prefer bare stranded copper. Bare wire is lighter
weight, of course, and solid wire is more prone to eventually breaking
due to flexing in the wind.
With only two or three radials, making them 1/4-wave long is a waste of
wire. You'd be better off using four to six radials half of that length
with the same amount of wire. Long radials don't pay off unless you have
a lot more than two or three.
For radials, either insulated or bare is OK. Because the antenna RF
current is divided among the radial wires, you can use a much smaller
size than #12. For the same amount of money you can buy more of the
smaller gauge wire and have a better ground system with more radials.
73, de Earl, K6SE
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