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

Stu Phillips stu at ridgelift.com
Sun Feb 21 17:08:15 PST 2010


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
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
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
as the screen changes pictures. I tried #31 toroids on the cable and AC
with very little help. The problem was finally resolved when a for sale
went up and that Viera left the neighborhood. 

Check your TV's first but if it's not yours get hold of a portable
receiver tuned to one of the peaks. I used 14.081.5 because it bugged me
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
hot but I have seen #31 toroids on the cable and AC help on lesser RFI

Another indicator is when the noise disappears late at night or is also
early in the morning when the set is not on. 

Once you locate the offending set get back with the group then we can
about how to tactfully convince your neighbor that their perfectly
TV is interfering with your radio.


-----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
* 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
* 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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