On Jun 3, 4:19*pm, Owen Duffy wrote:

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

Many thanks Owen. I just confirmed I have a BC interference issue.
When I placed a 100 ohm resistor across the 259B antenna terminal, the
unit correctly read 2.0 (well actually 1.9) swr, 100 ohms R and 0 X.
When it entered "battery save" the analog swr and impedance meters
both dropped to zero. The digital display stayed the same.

When I hooked my antenna up the analog swr meter only fell to 1.4 when
the unit entered "battery save" mode. The impedance meter did drop to
zero. When I installed a 4:1 balun at the antenna feedpoint the swr
fell to 1.2, but still not zero when the analyzer entered sleep mode.
Apparently the BC signal is at least to some degree differential in
nature on my feedline.

Anticipating all this, I wrote MFJ about the usefullness of their
their tunable analyzer filter to combat a strong FM broadcast signal.
They replyed that it would work. I wonder how well. The tunable filter
costs around $100.00.