[TowerTalk] Foam cables and velocty factor

Tom Rauch w8ji at contesting.com
Tue Nov 15 03:33:24 EST 2005

When ever I make a cable up, I high voltage test it for
voltage breakdown.
When ever I buy a cable, I test it for high voltage

Best thing I ever learned to do, besides washing my hands.

> I have two questions:
> a) Where in the spectrum is this 248 foot hunk of wire
resonant anyway!?
>     i) 1680 KHz (no reactance),
>    ii) 1800 KHz (minimum reactance & phase)
>   iii) 1850 KHz (minimum resistance),
>   iv) can't be determined from the data, or
>    v) depends on what the word "resonant" is.

The only thing we can say without backing through it with a
Smith chart is NOT on your target frequency. Minimum *SWR*
is probably where the antenna is actually resonant.

(I fought MFJ deperately to get them to avoid calling X=0 an
antenna "resonance" indication in the 259 analyzer series.)

> b) What will provide the best "performance" for this wire
at 1830 KHz?
>     i) Build a 2:1 matching device for the feedpoint,
>    ii) Trim the legs shorter to move the minimum vswr to
1830 KHz,
>   iii) Adjust the coax length to move the minimum vswr, or
>   iv) depends on what the word "performance" is.

Adjust the antenna until SWR is minimum at 1830. It makes
you feel good, that's why I do it

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