[RFI] advice wanted: finding the source of mixing products

[Matt NQ6N]

Jim,

> As noted above, that is NOT a meaningful test.

Interesting. I just did that test (kx2 tx, mains power off, portable
battery powered RX) and the mixing products are still there.

I realize based on your comment that I have a large number of
decommissioned wall warts around the shack which may be acting as passive
mixers.

Can I eliminate a wall wart from suspicion for causing this particular
mixing product if I hold the RX antenna near it and the signal level does
not increase?  I realize that the wall wart could be causing other
problems, but just trying to figure out a strategy for attacking what
appears to be the most significant source of mixing.

I have a lot of decommissioned wall warts around the shack that could be
causing problems as passive mixers, so I will gather those up and
remove them.

Two other observations:

1) Holding the portable RX antenna near certain mains outlets and light
switches seems to increase the signal strength of the mixing product at
14.786 MHz.  Is there a next diagnostic step that makes sense to test
these?

2) At the edge of the property are two boxes that appear to be owned by
AT&T. They are adjacent to the one that is owned by Comcast that my CATV
coax plugs into.  The portable receiver seemed to peak near the AT&T boxes.
However they are also near the folded counterpoise I use on my 160m
antenna. I'm going to try moving the FCP wires and testing whether the
signal still increases near those boxes.


Thanks again for all the help, Jim, Dave and others.

73
Matt NQ6N

On Mon, Feb 24, 2020 at 3:40 PM Jim Brown <jim at audiosystemsgroup.com> wrote:

> On 2/24/2020 1:03 PM, Matt NQ6N wrote:
> > Thanks much for the tips, Jim.  Do you know if the wall warts can cause
> > mixing when they are not plugged into the wall or if the circuit breaker
> > is turned off?
>
> They can cause mixing if connected to wires that can function as RX and
> TX antennas. And when operating, they produce noise which gets radiated
> and received by your antennas. SMPS are noise generators, which the
> major reason for a search out and destroy mission.
>
> > In my testing the other day I did not see any difference in the 14.786
> > MHz mixing product when turning off all of the breakers in the breaker
> > box. Does that test eliminate any warts on those circuits as culprits
> > for the specific mixing that remains present at 14.786?
>
> No, power is not required for them to cause mixing -- it's passive
> device in that regard.
>
> > My next test will be to power down the entire house and transmit with
> > the KX2 on battery, connected directly to the antenna, and confirm that
> > the mixing product is still there (eliminating anything in the shack
> > itself).
>
> As noted above, that is NOT a meaningful test.
>
> 73, Jim K9YC
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