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Re: [RFI] 120Hz period noise ID

Subject: Re: [RFI] 120Hz period noise ID
From: "Leigh L. Klotz, Jr." <Leigh@WA5ZNU.org>
Date: Tue, 06 Nov 2007 17:00:09 -0800
List-post: <mailto:rfi@contesting.com>
Summary: Just niw the neighbor's electrician removed a LighTech LET-75 
power supply and replaced the 12v light with a line voltage lamp.  The 
fixture was grounded, but the power supply itself had no ground lead.  
It was in a metal jbox atop copper pipes for water.

The company's site is http://www.lightechinc.com and the part is a "LET 
75 75 Watt Electronic Transformer LDC Dimmable."  It has RU markings but 
no Part 15, "Patented Made in China."  Their website is all Flash-based 
and hard to navigate, but you can eventually get to a data sheet, which 
has no mention of other acceptance.

He's sending it back to them for a refund, and plans to switch the track 
lighting to line voltage MR16's as well.


Leigh L. Klotz, Jr. wrote:
> 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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