These are annoying to track down, and I appreciate this because I am
currently working a few such problems. For the passive
non-linear/rectifying junctions, your only defense is essentially proper
bonding and grounding around said junctions (rotors, etc.) For active
devices (power supply rectifiers, diodes, etc.) you'll have to just remove
them from the equation (power them off, etc.) assuming that they're under
your control. If you have a particularly clean transmitter (like a K3S),
and you hear the harmonic noise 30+Kcs away from the harmonic at low power,
that's a good place to start when direction finding for the devices using a
small portal receiver, since your harmonic is probably not that
distorted/wide and a 'growly' noise (indicative of AC Hum) is a good sign
that a power supply is involved.
All I can do is point you to the great work by Jim Brown, K9YC, who
presented this talk at Visalia:
http://audiosystemsgroup.com/Multi-Station.pdf
--Bill/W9KKN
On Tue, Jul 23, 2019 at 4:46 PM Dan <w8car@buckeye-express.com> wrote:
> I am baffled by a problem that I’m having setting up to do interference
> free SO2R operating running LP. I’ve tried stubs and they have no effect on
> harmonics. I have good W3NQN style bandpass filters and THEY don’t seem to
> knock down harmonics. I know the stubs/filters are working as they greatly
> attenuate received signals if I put them on the band of harmonic
> attenuation. (40 meter filter in line while receiving on on 20 ) I’m using
> a K3 an FT1000MP. Filtering and stubs have no effect on either radio.
>
> I have read that there could be something other than the rigs creating
> harmonics. IE corrosion, wall warts, grounding problems. What I need are
> ideas on how to track these buggers if indeed this is the problem.
> Thanks in advance
>
> Dan W8CAR
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