We had to stop using 8405s in the field many years ago due to the external
RF problem Roy describes. Many of the newer analyzers use synchronous
detection which reduces the problem, unless the RF signal level from the
antenna exceeds the dynamic range of the instrument. Put a wideband power
meter or true RMS RF voltmeter at the measurement terminals and see how much
voltage/power is there from your antenna. You may have to wait for a
blackout to make measurements if the RF is from sky wave signals. If it is
ground wave from MW broadcast stations, move.

--
Crazy George
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