[CQ-Contest] SO2R filtering help
alan.higbie at gmail.com
Thu Jul 25 19:56:30 EDT 2019
Hi Andy ~
*Rig here*: Shack on is on second floor.
x2 K3's (with synth upgrade) + P3's;
u2R SO2R box;
5B4AGN LP BPF;
Not trying HP SO2R yet - but have ACOM 1000 -- with SPE 1.5 on order.
*Antennas*: 3 el SteppIR; 2 el Cushcraft on 40; inv. V on 80; and
(seasonally) inv. "L" on 160.
The SteppIR and 2 el 40 are on same tower with 15 feet in between. Pointing
in same direction.
*Changes so far*:
I changed replaced all coax (inside & outside) with double-shielded RG400 &
Installed more common mode choke baluns - including one at the feed point
of 3 el. SteppIR. & one for 80 closer to feed-point.
Completely replaced the half-assed control cables I had connecting my 2
K3s. This included getting N6TV's "Y" Boxes to tame the connections.
Used to have all coax come into shack - but now have pulled the 2x6 switch
out of shack and will do antenna switching in ground floor garage.
*STILL TO DO*:
Changing from Array Solutions 2x6 Six Pak to 2x6 by Low Band Systems switch
(remotely controlled from shack).
Already have (and will soon install) VA6AM High Pass Filters downstairs in
garage by the 2x6 switch.
Will upgrade bonding within the shack - its not bad now - but could use a
Will systematically install common mode chokes on control cables.
Eventually will re-route AC service to shack so it enters near where the
feed lines come in at the single-point ground panel.
*RFI detection - mitigation*
I have been keeping an RFI log of observations - for past couple of years.
And, I probably ALWAYS will.
For me, this will be an ongoing maintenance issue.
I have been successful in tracking and get power line problems fixed.
But currently I still have some intermittent (and significant) sources.
I periodically run an SDR to track all those little spikes, and to
determine WHEN the noise sources activate.
But like I said - I am following my friend's advice - and upgrading my
station to "best practices" standards.
It now seems, for example, that the 40 meter harmonic on 20 meters is
significantly less disruptive than before.
I used to see much more signal on the other radio's panadapter. So we're
The RFI seems to appear less often - and when it does, it is more limited.
73, Alan K0AV
On Wed, Jul 24, 2019 at 2:18 PM Andy KU7T <ku7t at ku7t.org> wrote:
> Hi Alan,
> *"My station's design & build, was making it more susceptible to RFI than
> it should have been."*
> Can you elaborate a little bit what you found was causing it, or what you
> removed and (likely) caused it? I am in teh same boat, 100W SO2R and S6 on
> 2nd receiver... Possibly a followup on the group would be good for everyone
> following this thread...
> *From:* CQ-Contest <cq-contest-bounces at contesting.com> on behalf of Alan
> Higbie <alan.higbie at gmail.com>
> *Sent:* Wednesday, July 24, 2019 7:00 AM
> *To:* Bill Fehring <bill+cqc at w9kkn.net>
> *Cc:* Dan <w8car at buckeye-express.com>; CQ Contest <
> cq-contest at contesting.com>
> *Subject:* Re: [CQ-Contest] SO2R filtering help
> 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
> 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
> 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
> 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:
> 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
> > 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
> > 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
> > 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
> > 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
> > > ideas on how to track these buggers if indeed this is the problem.
> > > Thanks in advance
> > >
> > > Dan W8CAR
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