[Antennas] Hy-gain AV-640 issues

Mon Apr 25 19:00:10 EDT 2011

Anthony R. Gold <ham-radio-mail-lists at ahjg.co.uk> wrote:
> Thanks for your various comments on transmission lines, but they did not
> answer my question. You deleted the paragraphs I was commenting on so let
> me recap: you wrote that VSWR reduces with increased line losses, which
> agrees with the arithmetic, but then you added that this relationship was
> only true if one used the line in some particular manners. I did not
> understand that last part. Can you give an example of a situation where
> one's manner of use of the line will change the relationship between
> increased losses and reduced VSWR?

I thought that was the question I answered.
Yes, I wrote that VSWR reduces with increased line losses; but I
qualified that by saying that it applies when you are using a line at
its intended characteristic impedance.
If you use a line at other than its characteristic impedance ... my
example being that you use a 125 ohm coax in a 50 ohm system ... then
the VSWR measured in your 50 ohm system, with increased line loss, can
increase rather than decrease.
Re-read what I wrote. With a half-wavelength piece of 125 ohm coax,
between a 50 ohm antenna and a rig designed to see 50 ohms, the rig
sees 50 ohms (a nice low VSWR) when the coax losses are low. But as
the coax losses increase, the VSWR the rig sees increases towards
2.5:1. In this case, higher loss causes higher VSWR, not lower.
Did you need another example?
Andy