[TowerTalk] Re; vertical base impedance

[Joe Subich, W4TV]

No disagreement ... *BUT* make sure the capacitor is rated to handle
at least 10A of RF CURRENT (or more with a short, heavily loaded)
vertical.  The feedpoint of a vertical is a high current, low voltage
point - the shorter the vertical, the lower the radiation resistance
and the higher the required current.  The voltage handling is only
important in the ability to withstand static/lightning.

73,

    ... Joe, W4TV


On 2025-03-17 4:12 PM, Richard (Rick) Karlquist wrote:
> It is very poor practice to make a capacitor out of a long piece of tiny 
> coax.  It will be very lossy (conductor loss, not the teflon 
> dielectric).  It is easy to simulate the bad news with Simsmith, etc.
> It is also easy to buy a 1206 NPO (Q>1000) 1000pF 1000V 1% capacitor 
> from Digikey, etc. for less than $1.
> 
> 73
> Rick N6RK
> 
> On 3/17/2025 12:42 PM, Joe Subich, W4TV wrote:
>>
>>
>> On 2025-03-17 2:01 PM, ARTHUR BERNSTEIN via TowerTalk wrote:
>>
>>> For a capacitor I used a long length of Teflon, thin coax @ 39 pf/ft 
>>  > (?)Actually coiled it up on a 1” form.
>>
>> Do you mean 29 pf per foot?  That's typical for the small diameter
>> 50 Ohm coax - RG58, RG303, RG316, RG393, RG400, etc.
>>
>>  > Total capacitance was about 1000pf +/-.
>>
>> With capacitance that high (reactance that low), one would be better
>> served to calculate the length of cable as an open stub (even if it
>> is rolled up) rather than simply as capacitance per unit length.
>>
>>  > It might have been  RG-302 or similar 50 ohm? Very thin, 1/8”?
>>
>> RG303 is 0.17", RG316 is .098", RG400 is 0.195" and RG393 is 0.39"
>>
>>