[CQ-Contest] SO2R filtering help

[Alan Higbie]

I'm not any kind of engineer.

BUT, I have a good friend who spent his professional engineering career
working in the EMC / EMI world.

I asked him how to troubleshoot RFI and inter-station interference problems.

He told me:
-- Philosophically there are two approaches:
(1) track down problems after equipment is built, OR
(2) design and build equipment to best practice standards in the first
place.

He also said: It was much harder to fix something that wasn't designed and
built right.

Thanks to the research, testing, writing, experience and presentations of
many of our brethren, we contesters now have access to those best practices.
For instance, see the K9YC link Bill / W9KKN mentioned in this thread.

Most hams have gradually pieced our stations together incrementally over
many years.

My friend suggested that before I started chasing RFI, I should first pull
things apart and re-build my station in accordance with best practices.

I'm now nearly done with that rebuilding process.  And the RFI /
inter-station interference is already much less.
My station's design & build, was making it more susceptible to RFI than it
should have been.

My next step is to track down (and eliminate) the remaining internal &
external RFI sources.

For anyone not already familiar with these resources, I highly recommend
the RFI Reflector:  https://www.contesting.com/FAQ/rf
Just lurking or searching the archives on that reflector provides a
graduate level education in the field. I.e. there are some really smart
people on there.

Also the ARRL's RFI resources:
http://www.arrl.org/radio-frequency-interference-rfi
Especially noteworthy are the ARRL's links to The Naval Postgraduate School
RFI Handbooks.

73, Alan K0AV





On Wed, Jul 24, 2019 at 6:27 AM Bill Fehring <bill+cqc at w9kkn.net> wrote:

> 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 at 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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