On 2/24/2020 2:03 PM, Matt NQ6N wrote:
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.
They must have antennas attached to function as mixers. An SMPS laying
in a drawer doesn't have much of antenna, so is unlikely to cause a
problem.
BUT -- if those decommissioned wall warts are LINEAR (they will be
larger and heavier than SMPS with the same power capability), you can
use them to replace SMPS. See that chasing noise tutorial.
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?
Yes
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?
The wiring to those outlets could be simply coupling to your radio's
antenna and extending it.
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 wouldn't expect an FCP to be part of a 20M problem generated by
something close to it.
I'm going to try moving the FCP wires and testing whether
the signal still increases near those boxes.
If the IM signal is stronger here than other places, it's possible that
it's the source. Or it may be the antenna coupling thing again. Both
boxes have multiple long antennas connected to them.
73, Jim
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@audiosystemsgroup.com
<mailto:jim@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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