[RFI] Inbound RFI - strange source affecting 160 and 80

Pete Smith n4zr at contesting.com
Mon Feb 22 02:54:50 PST 2010

I have something similar that I can now see with some new software and 
my QS1R - only mine are ~80 KHz apart, peaking about 2.2 MHz, and are 
broad.  I'd be glad to provide spectrum scope pictures to anyone who is 
interested - there is a central signal and a wide band of what sounds 
(on my transceiver) like simply an increased noise level.

Perhaps these both are switching power supplies, as someone 
knowledgeable suggested to me about mine.  If so, I haven't found it yet.

73, Pete N4ZR
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On 2/21/2010 8:08 PM, Stu Phillips wrote:
> Randy,
> Thanks but I don't think that's it...
> The signals are measured at 18 KHz apart using my Flex 5000 - the
> signals start somewhere around 1.7 MHz (tough to see them lower because
> of the AM band) and stop just under 5 MHz.
> In some cases, the RFI has continued for 24 hours solid in what I
> described as mode A.  Also, as I wrote originally, this has two
> different modes that often run for days at a time.
> TV sweep was one of my first thoughts too until I measured the frequency
> and then saw the two different modes.
> Stu K6TU
> -----Original Message-----
> From: WX5L [mailto:wx5l at charter.net]
> Sent: Sunday, February 21, 2010 4:33 PM
> To: Stu Phillips; rfi at contesting.com
> Subject: RE: [RFI] Inbound RFI - strange source affecting 160 and 80
> Horizontal sweep noise from a nearby TV. Actually it's 15.75 kHz and so
> full
> of harmonics that it carries well into the HF band. It couples with the
> cable input which acts like an antenna very nicely. It also couples with
> the
> A/C input.
> I've found most LCD are quiet but plasma's and older CRT TV's are a
> different story.
> Three houses down about 600 feet was a Panasonic Viera that screamed
> horizontal sweep. If you listen closely you can hear the RFI change in
> pitch
> as the screen changes pictures. I tried #31 toroids on the cable and AC
> cord
> with very little help. The problem was finally resolved when a for sale
> sign
> went up and that Viera left the neighborhood.
> Check your TV's first but if it's not yours get hold of a portable
> shortwave
> receiver tuned to one of the peaks. I used 14.081.5 because it bugged me
> on
> RTTY so much.  Do some walking around the neighborhood listening to that
> raspy note until you get it strongest.
> There was not much I could do with that Viera since the emissions were
> so
> hot but I have seen #31 toroids on the cable and AC help on lesser RFI
> emissions.
> Another indicator is when the noise disappears late at night or is also
> gone
> early in the morning when the set is not on.
> Once you locate the offending set get back with the group then we can
> talk
> about how to tactfully convince your neighbor that their perfectly
> working
> TV is interfering with your radio.
> 73,
> Randy
> WX5L
> -----Original Message-----
> From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
> Behalf Of Stu Phillips
> Sent: Sunday, February 21, 2010 5:08 PM
> To: rfi at contesting.com
> Subject: [RFI] Inbound RFI - strange source affecting 160 and 80
> I'm wondering if anyone has seen an RFI source like this before?
> * At isolated (and generally short) periods, the RFI is gone.
> * It has two modes...
> * Mode A - like the pattern from my first RFI Hunters post, a repeating
> pattern every 18 KHz with a central noise "splodge" about 3-4 KHz wide
> with two "sidebands" equally spaced +/- 5 KHz from the center of the
> RFI.
> * Mode B - a 500 Hz "spoldge" of noise repeated every 18 KHz
> * Both modes appear to have multiple "sub-carriers" within the noise -
> it's hard to tell but it appears that these carriers carry some form of
> modulation.
> * Both modes exhibit excellent frequency stability
> * Both modes deliver about -76 dBm into my receiver - that's around 35
> micro-volts - pretty hot!
> * Some patterns have emerged... typically early in the morning before
> 7am, mode B is present. It has transitioned to mode A several times at
> 7am and continued in this mode until about 9am. Then it reverts to mode
> B. At the weekend, its often in mode A all day long...
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