Did reply directly to Dave NK7Z by mistake, omitting the reflector.
Sorry, and 73,
Mike, K8CN
________________________________
From: Michael Carter <Mike.Carter@unh.edu>
Sent: Sunday, December 21, 2025 8:23 PM
To: Dave (NK7Z) <dave@nk7z.net>
Subject: Re: [RFI] Odd RFI case I'm working on...
Hi Dave,
Put large clamp-on ferrites on the flex tubing hoses at the hot water inlet and
cold water outlet ports of the pump. Even if those pipes are 'grounded', the
impedance presented to any RF currents on the pipe exterior surface may be
inductive and high, which negates the value of the 'grounding'.
Does the pump RFI occur on all HF bands or just a few? That is another clue.
Does the house have PVC plumbing, copper plumbing, or a mix of the two?
You've done all the obvious electrical fixes, albeit temporary in some aspects,
and the fact that RFI persists even at reduced power levels suggests to me the
RF ingress is via the water lines. If adding choking impedance on the AC
supply cord (i.e. , multiple turns of the cord on a large toroid) doesn't fix
the RF ingress, I would look at the cold and hot water feeds.
Before doing that work, I would set the clock timer (if this older unit has
one) so that the pump controller is disabled. Test for RFI in that state - if
the pump is not kicked on by external RF, then I'll be more convinced the RF
ingress is via the water lines themselves, specifically RF currents on the
exterior surfaces of conductive pipes (or the metal braid sheathing on flex
plastic hoses).
73,
Mike, K8CN
________________________________
From: RFI <rfi-bounces+mike.carter=unh.edu@contesting.com> on behalf of Dave
(NK7Z) <dave@nk7z.net>
Sent: Sunday, December 21, 2025 7:09 PM
To: RFI Mail list at contesting.com <rfi@contesting.com>
Subject: [RFI] Odd RFI case I'm working on...
CAUTION: This email originated from outside of the University System. Do not
click links or open attachments unless you recognize the sender and know the
content is safe.
Hello RFI group,
I have an RFI case I am working on right now, that has stumped me
completely...
A fellow Amateur has an Laing under sink recirculation pump model
ACT-303-BTW. Every time he transmits, the pump kicks in. The following
steps have been tried.
1. A Pile of clamp on ferrites have been added to the short power cord,
maybe 5 of them. No room yet to wind on an FT250-31, but that may be next.
2. The water piles have been connected to ground, using a car jumper
cable. The person who put this on tells me he used the ground on a
outlet... Yes, we will test differently with a real ground at some
point soon.
3. He has reduced power to 50 watts and the pump still kicks in.
4. He has wrapped the pump in foil, and grounded the foil. Again, I am
sure via the outlet ground.
5. His dipole, which is close to the home, has a quality Balun Design
choke on it at the feedpoint.
6. The coax has been rerouted to as far as possible from the device as
possible, running on the ground as a test.
The device is an older one, and sits under the sink. The ham is not
sure if his cold water pipes are at actual ground.
I intend to do the following:
1. Use a real ground, if needed to ground the cold water pipes to the
service ground then bond to the pipes at the pump.
2. Replace the power cord with a longer version, and wrap 12 turns of
AC line cord in an FT240-31, and/or add an external RF filter to the AC
line.
3. Reduce power further to try and pin down where the RF is getting in,
pipes, or power line by isolation.
Purchase a good RF filter for the AC line. Can someone suggest an OTS
one I can recommend? He operates 80-10 Meters...
Any other ideas?????
73, and thanks,
Dave (NK7Z)
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