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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 10:58:50 -0700 (PDT)
List-post: <mailto:rfi@contesting.com>
Mike, Dave, and all,

My neighbor and I have tracked it down with 95% confidence to a
wall-mounted light dimmer controlling a socket into which is plugged an
overhead lamp.  She turns dimmer on at night and off in the morning, which
matches the pattern I've heard.  We didn't want to disturb the baby last
night but it seems like I said 95% certain that's it.   It was off when
she came home, then the baby went to sleep and it came on, and then this
morning it went off when she left the house.  The neighbor is amenable to
replacing the dimmer with the Lutron model recommended by the ARRL and
I'll be working with her on that, and she'll have her electrician replace

However, I believe there's a second problem which is exacerbating the
noise by radiating it and I'm looking for some advice about what to
recommend for her to tell her electrician to look for.

The noise is present inside my own house in my water heater, and loud at
my gas meter.  It's loud at her gas meter too, and the two gas lines (one
black pipe) that come out of it, and her water heater, which was recently
moved outside into a shed-like structure built for it (destination of one
gas line).  It's also noisy along the fence line where our gas lines run
underground.  Her gas line is right next to a small electric conduit that
enters the house, and it's really noisy there too, when I use my small
nulling loop, so I suspect the gas line is picking it up there.

The neighbor said an electrician was involved in the water heater work in
the first place, but I noted no bonding anywhere, though there's probably
a ground rod at the service entrance which is only a few feet away.

Since the gas pipeline is radiating like crazy and runs next to the
electric conduit which is presumably carrying the noise, and since the
water heater doesn't look bonded nor the gas line, I'm thinking there may
be some NEC problems here and she should get an electrician out pronto to
make sure they don't get 120VAC onto the hot water line or the gas, in
addition to possible added benefits of not turning the neighborhood gas
system into a big antenna for her noisy appliances.  In my own house,
there's bonding between the water heater and service ground, and the gas
pipe and service ground, all done to code by the contractor.

Any suggestions on what I should tell her to tell the electrician when she
calls?  Is "My water heater isn't bonded and the gas line isn't bonded?"
enough?  Is there some section of NEC I should point them to so that she
can be sure she's got an electrician who's going to do the right thing for
both safety and radiated noise in the future?

73 es TNX,
> I have a buzz that happens some, but not all, nights, and not during the
> day, at least so far.
> On HF, I can hear it 80-20; I haven't tested other bands.
> Here is a screenshot of what it looks like in an SSB receiver:
>   http://wa5znu.org/2007/10/rfi/rfi.png
> The axes are in ms, and the period is close enough to 120Hz that I think
> that's what it is.
> Here's what I've done so far:
> 1. Rotated a 20m beam and found the general direction, with about a 35
> degree beamwidth.
> 2. Used a simple wire loop on a TH-F6a set for AM on ~5Mhz and found
> it's not coming from my house.
> 3. Found a strong buzz coming from the sodium vapor light in front of my
> house, but it could also be just coupling from the light mast as an
> antenna (same effect for WWV on 5 MHz).
> 4. There is no correlation between the sodium vapor light being on or not.
> 5. I haven't heard it during the day.
> 6. I haven't heard it every night.
> 7. There are other power lines around in the general direction.
> 8. I've been able to hear it from the light mast on 135Mhz but the wire
> loop isn't sensitive enough to find it at a distance; I will probably
> make a wire yagi if I need to do more looking.
> So, does this look like power line noise?  Or should I be looking for
> something in a neighbor's house that they use at night that also somehow
> emits broadband noise with a 120Hz period?
> 73,
> Leigh/WA5ZNU
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