Topband: Air Wound Coil

[Grant Saviers]

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
>