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Re: [RFI] 120Hz period noise ID

To: rfi@contesting.com
Subject: Re: [RFI] 120Hz period noise ID
From: "Leigh L Klotz, Jr." <Leigh@WA5ZNU.org>
Date: Tue, 30 Oct 2007 23:04:05 -0700
List-post: <mailto:rfi@contesting.com>
The neighbor's electrician came over and after a few minutes of problems 
due to a loose SMA connector on my TH-F6, we found there are two problem 
lights: one an S3 and one S9+20.  Neither was the light I first 
suspected, but both were indeed lights.

S9+20 was an SMPS in the ceiling powering a single 12V Halogen light on 
a Lutron dimmer.  The dimmer is not the problem, and jumpering around it 
showed no change.   The SMPS is in a metal j-box but is ungrounded and 
is run with 2-wire in and sits very near the hot water pipe and several 
other conduits, so I asssume that's why the pipes are radiating.

The electrician checked the grounding and bonding of the pipes outside 
and said all was to code.  He said that in our city, they do not want 
the gas line bonded.  We verified no other equipment was making RFI 
(pool pump, heater, dishwasher, etc.).

The good news is that the electrician plans to replace the in-ceiling 
SMPS with a transformer.  I showed him a similar LV lighting system I 
have (no dimmer though) and how it was 100% quiet with a transformer.  
He seemed to think that the "electronic transformer" was superior 
because it was quieter, though presumably that's acoustic noise, so 
watch out for this tendency if you encounter this situation.  He did say 
that he used only Lutron dimmers.

The S3 noise is a bank of individually-controlled Juno track lights on 
120VAC rails, each an MR16 or MR12 with an internal SMPS.   We haven't 
digured out a plan for them yet.  He seemed to think fixing this problem 
was optional, so I showed the electrician (not the homeowner) the ARRL 
collection of FCC letters on lighting systems, and told him his first 
stop should be the manufacturer.  He said he would check with a 
colleague who does hi-end audio systems and has some experience for 

One last: about 30 minutes after I left, we had the biggest earthquake 
in 18 years.  I headed back next door with the same HT, now listening to 
USGS and individual reports from around the Bay Area instead of a 
horrible buzzing sound, and the neighbor said, "I'm sure glad we have 
you next door!"

I will report back if the mitigation measures don't work, or if I need 
help on them, but other than that, I think we're done here.


On Tue, 30 Oct 2007 3:28 pm, Leigh L Klotz, Jr. wrote:
> Thank you Jim and all.
> The bad news is the neighbor called to say she had not turned off the
> nightlight this morning, so it must be something else.  So we are in 
> the
> 5% case.  Then her electrician called and I am meeting him in about 3
> hours.  He thinks it is the heater and is ready to look at bonding.  I
> will bring the info from
> Jim K9YC.
> 73,
> Leigh/WA5ZNU
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