[TowerTalk] Re; vertical base impedance

[Richard (Rick) Karlquist]

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"
> 
>