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@contesting.com [mailto:rfi-bounces@contesting.com]On
> Behalf Of Tom Rauch
> Sent: Wednesday, October 06, 2004 11:18 AM
> To: wx5l@charter.net; Jim Miller; Bill Gaines; rfi@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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