Coaxial cables have loss.
With long cables it is best to match the antenna to 50 ohms before
connecting it to the cable. If this is not done, a mismatch between the
cable impedance and the antenna reflects some power back to the
transmitter. The cable loss dissipates some of the reflected power and less
of it is reaches the transmitter than was actually pushed back by the
antenna.
If the cable is mismatched at both the antenna and transmitter ends, then
part of the power reflected by the antenna travels back and forth between
mismatches creating further losses in the cable.
Power lost in the cable does not get radiated and does not show up as bad
VSWR at the transmitter end giving the false impression of a better match
than is actually present.
__Joe VE6JSL
On Mon, Aug 7, 2023 at 09:06 Zack Widup <w9sz.zack@...> wrote:
I generally measure it at the end of the coax in the shack. That way I see
what the rig is going to see. I have had really long stretches of coax to
the antenna and the NanoVNA was unable to measure the SWR. I think it
required more power to overcome cable losses. In that case I had to check
it with a lot shorter length of coax.
73, Zack W9SZ
On Mon, Aug 7, 2023 at 9:47?AM Peter N0PGM <pgmelton@...> wrote:
Hello,
Once my antenna is up it will have a 50ft run of coax that enters my
home.
Do I measure the swr at the base of the antenna (before the 50ft of coax)
or inside the house (at the end of the coax)?
Thanks in advacne,
Peter
--
__Joe Leizerowicz
6424 34 Avenue NW, Calgary, AB T3B 1N1
403-604-7791
