[RFI] Chasing RFI

Christopher Brown cbrown at woods.net
Sun Oct 18 18:11:36 EDT 2015

On 10/18/15 09:24, Jim Brown wrote:
> On Sun,10/18/2015 8:51 AM, Charlie Gallo wrote:
>> Any ideas how to proceed from here?
> Some questions to help you think about it.
> As you tune around a band, especially the lower bands, are there peaks 
> of noise, with a center that sound like a growly tone? If yes, this 
> noise is not power-system related, its an electronic source. And, of 
> course, you could have both kinds of sources. Many of us do.
> A great way to figure this out is to look with a spectrum display, 
> especially one with a waterfall. Electronic sources will show bumps of 
> noise, spaced 10-20 kHz across a band, and if they drift, they're 
> switching power supplies. If they don't, they're running on some sort of 
> clock, usually associated with a microprocessor. They will show up as 
> straight vertical lines on a waterfall, wiggly if they're a switcher. 
> Power line noise is impulse noise, and will show up as horizontal lines 
> on the waterfall.
> 73, Jim K9YC

I have a SDR-14 and rigged a "portable" setup (flat plate with a
gel-cell and places to velcro the SDR and laptop) for exactly this.

Don't exclude wider spaced though, switchers and similare are sometimes
running at higher frequencies.  I have several switchers that run in teh
40 - 60Khz range, and some of the new audio amps (class D and I think T)
are basically PWM at around 300Khz.

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