[NLRS] 6 Meter interference question

[jcplatt1 at mmm.com]

Hi Patrick.

When trouble shooting this type of problem the key is trying to determine
if the interfering signal is real or not.     Whether its real or not
determines how to fix it.

Your note contains two significant clues.   The first clue is that when you
face your beam north or south the signal is very strong, but when you face
east or west, you do not "experience the problem" (does this mean you don't
hear the signal ?).    No beam in the world has this kind of front-to-back
ratio (that could make such a strong signal disappear).    The second clue
is that when you turn on the attenuator the signal "completely disappears"
.... this is a classic clue.

Both of these are strong clues that something inside your radio is being
overloaded and that this internal overload is generating the interfering
signal that you are hearing, the signal is not real.    The overload may be
due to one, or several, very strong out of band (not 6m) signals that are
doing evil things inside your radio.    Anytime you can flip in 10 dB of
attenuation and the signal changes by more than 10 dB, the signal isnt
"real", its sometime else.

As has been suggested, the fix is to get some front selectivity and/or
notch out the problem signal (Ch 3 ?).    I think there were a couple of
suggestions to try out a low pass filter that has a cut off freq above 50
MHz (passes 50 MHz) but below the Ch 3 freq (attenuates Ch3).    There are
some commercial filters that can do this and you can also home brew
filters.   Most of these are designed for 100 watts.   Pay attention to
what the cut off frequency is and how much attenuation is offers at Ch3
.... that may allow you to do some filter spec comparison.     Such a
filter should have almost no affect to your 6m signal.

73, Jon
W0ZQ