I have revised my question to correct the length of the antenna in question
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 5/8 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 5/8 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
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|