"Roy Lewallen" wrote in message
...
Tam/WB2TT wrote:

If you are going to buy new coax, might as well get something decent. I
used RG11 FOAM for a 1/4 wave transformer at 3.8 MHz, and it worked per
theory.

I think you were lucky. I've found that the velocity factor and
characteristic impedance of foam dielectric coax, even quality coax, to
vary a lot more than solid dielectric cable. Apparently they don't have
very good control over the foam density.

Roy Lewallen, W7EL

I didn't have the exact Vp number for the SIW cable; so, I trimmed it.
Length came out reasonable, though. If I measure a 50 Ohm load through the
cable, my MFJ269 reads 102/J0 at resonance. A little on the low side, but
probably within tolerance. If it was not raining outside, I would measure
the cable to see what exact length I ended up with. Bottom line is that my
(late) 75 m loop did have an SWR of 1.1:1 at resonance.

Tam/WB2TT