[RFI] 160 Meter Interference

Hare, Ed W1RFI w1rfi at arrl.org
Mon Oct 11 17:48:41 EDT 2004

In most cases, switch-mode supplies tend to run at a fairly steady frequency, but with slow drift from a cold start to full warmup.

The other thing I have noted about most switchers is that the inevitable line surges or sags tend to make them burble for that fraction of a second.  So if they are steady, but once in a while hiccup, think switcher.

Ed Hare, W1RFI

> -----Original Message-----
> From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com]On
> Behalf Of Tom Rauch
> Sent: Wednesday, October 06, 2004 11:18 AM
> To: wx5l at charter.net; Jim Miller; Bill Gaines; rfi at contesting.com
> Subject: Re: Re: [RFI] 160 Meter Interference
> The 90kHz spacing and reasonably clean carrier is a dead
> giveaway. 90 kHz is in the most common range of low or
> medium power switching power supplies. The carrier was
> basically clean except for minor ripple. It had very little
> frequency wobble caused by changing data or a changing load.
> While it certainly could be from a power supply in a digital
> device, it almost certainly would be from the power supply
> section. It very clearly had all the characteristics of a
> power supply with a steady load, which means it could be
> anything from electric lights to battery chargers to line
> operated consumer devices of any type.
> Best way to find it is to drive and listen, and watch the S
> meter.
> I found a computer over a mile away (airline) that had a
> devastating SMPS backfeeding the power line in differential
> with the modem connection to the telco line. It was S9 +15dB
> at my house compared to an S1 background noise here, which
> in more meaningful terms (since my S meter like nearly all S
> meters is not 6dB per S unit) was about 40dB out of my noise
> floor. The actual conducted path via driving along the wire
> was nearly three miles, so this crap can go a long distance
> and be strong!
> 73, Tom W8JI
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