Topbanders
In the past, I've posted some questions related to making my 80 meter verticals
(64' tall ground mounted) work on different bands. The pair is spaced at ¼ wl
on 80m and then I switch in base loading to resonate the same pair on 160m
which are then effectively spaced at 1/8 wl. Now I want to make them work on
40m which would have them resonate as ½ or 5/16 or 3/8 wl and would have an
effective spacing at ½ wl.
So this is what I did...I installed an L network off of the vertical
effectively tuning a 64' stick of aluminum to 7.050. It took me a couple of
tries as the first 1500pF (monster) variable capacitor wouldn't get down low
enough to get me flat. I had another 50-150pF Johnson variable cap available
so I tried that and got the antenna to tune to 46 ohms at j+0. Inside the
shack I see 1.0:1 Vswr from 7.000 to 7.290...wow!
I measured the cap and it came to 70pf. My cheapie Chinese meter doesn't
register anything on the L scale but I have 7 turns on a 3 ½" inductor. The
full coil is 33 uH at 25 turns so I estimate 8-12 uH of inductance.
But what have I done? Have I resonated a ½ wl antenna or have I resonated
something else like a 5/16 wl or even a 3/8 wl antenna with the added
inductance?
I plan on treating them as ½ wl spaced phased verticals on 40 and feeding them
with equal lengths of ¾ wl feedlines for broadside phasing and then adding an
additional 2/4 wl to get my 180 degree shift for end fire.
Please share your comments.
thanks
Carl de AG6X
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