TopBand: Cap for inverted-L...

[N7EX]

Swanson, Glenn, KB1GW wrote:
> 
>      Greetings,
> 
>      Okay, so I'm thinking about extending my 1/4-wavelength "inverted-L"
>      out to 170 feet (+/-) and putting a (air-variable) capacitor at the
> feedpoint.
>      I know I'll need something like a 500 to 1000 pf cap. However, what
>      voltage rating? And, if you have a brand/catalog number, that'd be
> great.
> 
>      Enjoying the TopBand chatter (well, most of it, anyway) and look
> forward
>      to any replies to the above question(s). Have fun on the gentlemen's
> band.
> 
>      73, Glenn, KB1GW
> 

Glenn

Since the cap is in series with a "current" point on the antenna. HV
ratting is not as important as current ratting. a 2KV cap should be
plenty. In fact If you can build a suitable enclosure then even Air
variables work quite well. I use a 150pf air variable shunted with
several of the old surplus 100pf transmitting micas (the brown ones abt
2" square). For example to 500pf TV style doorknobs wont work because
they cant handle the current (they get warm even with 100 watts) even
though they are rated 15kvto 20kv. At 1KW the current can be on the
order of almost 6 amps (more on  on peaks). If you plan on using the
antenna on other bands (say with a tuner) then be careful you can end up
at "voltage" node on another band and blow the caps!I that case the
vaccumn variable is more likely a better bet. I have had the best luck
finding vacumn varibles at HAM fests I have paid anywhere from $35 to
$80 for them.

Dave
N7EX

PS: I have two L's in this configuration fed in phase...good luck

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