On Jun 3, 4:19*pm, Owen Duffy wrote:
dykesc wrote in news:22d6efc6-76ca-487a-9fc1-
:

...

I am concerned about an RF field from a local broadcast that may be
causing issues with using the low power MFJ 259B. When I use the auto
tuner I am tuning at 10 watts so plenty to counteract any local rf on
the antenna. I really need to back calculate an impedance from the
inductor, capacitor, and final swr from the auto tuner.

Why didn't you say that the first time?

Guess I was in a hurry and just wanted to know if I could back
calculate the impedance (R +- jX) my auto tuner is seeing based on the
inductor, capacitor and final swr values it displays after a "match is
achieved. I would still like to do this. Dave gave me a link and of
course I can do it manually with a Smith Chart (I think lol).


Tom Rauch (one of the designers of the '259B) posted this info re
interference:

"BC interference causes the bridge in the analyzer to remian (sic)
unbalanced even with very low SWR, so the analyzer will read a fixed
minimum SWR when BC interference. It will read that way on any frequency
from dc to daylight. For example if the unit falls asleep the SWR meter
won't drop to zero. That's an indicator of BC interference or external
voltages being applied to the measurement port."

Owen

Thanks. Now there's a bit of info I didn't have. So if the 259B is
behaving normally, when it enters "battery save" mode the swr value
should drop to zero. If not, there are external voltages on the
antenna port. I think I will check this out with a 100 ohm resistor
across the antenna port. 2.0 should drop to 1.0 or zero when "battery
save" kicks in.

By the way, the broadcast station is FM at 105.5 MC.