[600MRG] Vacuum variable capacitor, low-pass/band-pass filters

[John Langridge]

>His reaction was that the voltages for my 630m station
> couldn't be more than what is seen in AM BC equipment,

not necessarly true because when we use ohm's law in the reactance
form, E = IX, X is probably going to be a lot greater in your
application than in a BC application.  Current will likely be lower
but consider N1VF's apartment loop.  Ben's Vac Var was seeing about
1700 volts for a reactance of about 300 ohms and the current he was
measuring (I forget how much I without looking and dont have a
calculator on me at the moment)

I'm not here to say that you can't make it work but just realize that
you might open yourself to other complications later...

73!

jl




On 6/22/19, Frank O'Donnell <600 at inkbox.net> wrote:
> Thanks to everyone for the great responses. Those sound like promising
> ideas on both the capacitors and filters, and I will check them all out.
>
> One question for now. I mentioned my interest in a vacuum variable
> capacitor to a local ham friend who has a background in the AM broadcast
> industry. His reaction was that the voltages for my 630m station
> couldn't be more than what is seen in AM BC equipment, and he thought I
> might be able to scrounge a cheaper air-dielectric variable cap that
> would be adequate. Is the preference for vacuum caps due to the fact
> that they are more compact? Or more available? Or are there other
> reasons for going with them?
>
> Actually, make that two questions for now: Regarding voltages. What sort
> of voltage rating should I be looking for in any of the caps (variable
> or fixed) to tune the ~120-foot-circumference vertical loop?
>
> Thanks again, and 73,
>
> Frank K6FOD
>
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