Bob, K6ZZ wrote:
>Yet another quick question for the gang... I'm getting ready to purchase
a
>motorized vacuum variable cap for the Gamma Match on my shunt fed tower.
>Looks like about 50-150 PF will be needed for a match. The higher the
>voltage rating, the better. Just curious though, would a 10-1000 pF
vacuum
>cap with a 3 KV rating be sufficient for the task, assuming maximum
legal
>transmit power is used (1500W)? I've run the calcs 2 different ways and
get
>different answers each time! Thanks again.
====================
If you know the required value of capacitance, this formula will yield a
close approximation for 1500 watts applied to the antenna:
Volts across cap = 475,000/capacity in pF.
For 1000 watts, use 388,000/capacity.
A shunt-fed vertical on 160m can require a gamma capacitance value of
anywhere from about 75 to 600 pF. If the structure is electrically
1/4-wave, the largest value of capacitance is needed (least voltage).
Less capacity (larger voltages) is required when the structure is
electrically longer (up to 1/2-wave) or shorter than 1/4-wave.
73, Merry Xmas, de Earl, K6SE
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|