[CQ-Contest] Diode RFI

tgstewart at pepco.com tgstewart at pepco.com
Mon Dec 6 10:20:39 EST 1999

I think some people dont realize that one of the biggest contributors to station
interference is your house wiring.  Your house wiring is a big antenna and if
you let any RF leak across "the bridge" between it and your station equipment,
you are asking for trouble.

You can solve lots of possible troubles simply by using RF filtered power strips
on all your equipment.  This will catch most bad power supplies, etc., in the

Also be sure that your computer power supplies have CE or FCC or UL (CE is the
best safeguard) stickers on them.  Some el cheapo cases come with unrated power
supplies with no AC lead filtering!  This will pollute your RF environment for

Wallpack power cubes with DC outputs are notorious for producing noise from
unbypassed diodes.  Plugging these into a filtered strip will reduce radiated
noise considerably.  Adding ferrite to the output lead is probably a good idea
for those with trouble, but doing surgery with bypass caps is the best solution.

To:   contest reflector <cq-contest at contesting.com>
cc:    (bcc: Tyler G Stewart/BENN/CEC)

Subject:  RE: [CQ-Contest] Bandpass filters

> > Anybody have any experience with this same problem? I have notice
> > the LEDs flashing before to the cadence of the RF, so I thought perhaps
> > they were acting like noise generators.

It's quite possible that an unbypassed LED can generate wideband spurious
emissions in the presence of strong RF.

I had a similar experience with Tailtwister rotor control boxes - the
rectifiers in the control box are unbypassed.  The strong local AM BC
signals (there are 6 within five miles) came down the control lines, were
cheerfully mixed together and evenly distributed all over 40-meters, in my
case, and probably elsewhere.  The solution was to bypass all of the
control lines at the terminal strip to the control box with 1000 pF
ceramic caps. Problem solved.  This could cause serious spurious problems
at multi-radio setups wherever similar rotor boxes are in use.

In this case, it sounds like RF is leaking in via the control port.
Bypass all the lines to ground - outside the case if possible - with 1000
pF ceramic caps.  Make sure the case is solidly grounded, as well.  If the
bypassing can't be done outside the case, do it at the back of the control
port connector and put a big ferrite core on the control cable, as well.
If the LEDs are still flashing after this treatment, I'd go after the
power supply next.

73, Ward N0AX

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