Me too.
Or the inverse as I did, cut my T for the low end of the band. Then
three series capacitors with PCB relays to short each individually
(none, 1, 2, or 3) yielded nearly full band coverage <1.5:1 swr. My T
is 85' to top and a 50:25 ohm TLT is a close match, then the capacitor
stack follows. Caps and relays fit in a weather tight plastic box about
3x5x8". Of course the resonance resistance and capacitor values depend
on the antenna geometry. EZNEC easily models this antenna. For me all
three caps were 4000pf. Relay settings of short, 4000pf, 2000pf, and
1333pf moved resonance in about equal 40KHz upward steps. Instant QSY
and cost about $100.
With 12.5 ohm resistance, QRO current will require 3 or 4 silver micas
in parallel for each C. Check the current ratings for the CDE CD/CDV16
series micas. Voltage is easily managed with 1000v rated caps since
when in series they become a voltage divider.
Grant KZ1W
On 9/1/2018 13:17 PM, W7RH wrote:
Guys, I'm confounded by the complexity suggested for all band coverage
of 160m "Top Loaded T Antenna".
May I make a simple suggestion. A simple T antenna will have a
radiation resistance of 10-12 Ohms with electrical height of say 43ft
with a Good ground system of quarter wave radials. By trimming the top
load portion (both legs equal) to resonance on the high end of the
band 12 turns of quarter inch copper tubing wound on a 4 inch ABS pipe
with length of 12 inches and three relays would provide entire band
coverage when connected to 12.5 Ohm Un-Un transformer. Cheap generic
DPDT relays may be used to switch resonant points and can handle legal
power limit.
Just sayin...
Bob W7RH
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