Ah, yes, he's measuring "insertion loss" in a system with fixed source
and load impedances. This isn't only dissipative loss (although it can
include dissipative loss), but rather is the "loss" or reduction in
signal received at a fixed load. This reduction in signal is caused by
the combination of real, dissipative loss and that due to mismatch
between the source and load (known as "mismatch loss"). For example, if
you had a piece of completely lossless 75 ohm coax between the source
and load in his (typical lab) test setup, you'd measure 0 "insertion
loss" if the line was exactly a half wavelength long, 0.18 dB if the
line were exactly a quarter wavelength long, and other values depending
on the line length. This isn't due to any loss in the cable, but to
reduction in the signal dissipated in the load due to mismatch when
using a fixed source impedance.

If we put a matching circuit at either end of the coax, we can make the
"insertion loss" completely disappear, by restoring the impedance match.
In a typical amateur antenna installation, we do use a matching
arrangement to insure this impedance match. Therefore, any "insertion
loss" due to mismatch is eliminated. All that's left is any true,
dissipative loss. The mismatch loss VE3JEG measured is, I believe,
nearly solely mismatch loss.

I've posted a fair amount on this topic in the past. You should be able
to find the postings with a groups.google.com search of this newsgroup
for postings by me containing "mismatch loss" or "insertion loss".

Roy Lewallen, W7EL

Ivan Makarov wrote:
Read he
http://www.qsl.net/vk3jeg/pl259tst.html

--

Regards,
Ivan

VE3IVM

"Ken Bessler" wrote in message
news:uS7jd.15068$Vz4.14651@okepread01...

I'm aware that the PL-259 has loss but what I'd
like to find out is how much loss at 146 & 450 mHz?

Anyone know?

Ken KG0WX