Peter wrote:

Roy

All comments noted. I do in fact live within 2km of an AM transmitter
although I believe it's not that high powered and I also have an FM
transmitter within 5km, therefore I'm interested in the details of your
location in relation to the various transmitters.

Regards

Roughly 10 - 15 miles from here is a ridge about 800 feet higher than my
location. On top are virtually all the TV and FM, and a number of the
AM, transmitters for the Portland Oregon metropolitan area. A single
strong transmitter is likely to be enough to confuse an antenna
analyzer, though. Filtering is possible, of course, but you have to take
care to design filters to have minimal effect on measured impedances
while still filtering effectively. This can sometimes be challenging
depending on the strength of the interfering signal and how far it is
from the measurement frequency.

I also have to be careful when working on audio circuitry -- on several
occasions I've tracked down "hum" as demodulated TV video, and I end up
having to include VHF decoupling and shielding to audio circuits. Don't
know much about the nature of HDTV signals, but it might not be so bad
if it doesn't have as much energy in the AF range when demodulated. It's
bound to drive untuned antenna analyzers bonkers, though.

Roy Lewallen, W7EL