On Wed,10/8/2014 10:19 AM, Hans Hammarquist via TowerTalk wrote:
I decided to also check the velocity factor. I was a little puzzled to get a
factor of 0.8. Does that make sense? It's a foam filled coax. I expected
something around 0.9.
A couple of comments. First, Vf varies slightly with frequency
(typically 1% between 2 MHz and 50 MHz. How did you measure Vf?
Measuring the resonant frequency of the line as a stub will yield the
value at at that frequency. Measuring TDR by doing an FFT of a VHF sweep
will yield the VHF value.
Second, all foam dielectrics are not the same. I have foam dielectric
coaxes with values between about 0.78 and 0.88 at VHF.
I suggest you dig up the mfr data sheet for the coax you have. The
published Vf will be the VHF value.
There's a discussion of this in k9yc/com/Coax-Stubs.pdf
73, Jim K9YC
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|