[RFI] RE: Cable Modem RFI/EMI

Peter D. Vouvounas wb3fsr@home.com
Fri, 30 Nov 2001 10:44:31 -0500


Morning - Seems I have all of the utilities working to clear various RFI
issues these days Comcast - GPU etc.

Just yesterday the cable guys (wasn't that a movie) were out with their
sniffers looking for leaks after a bit of prodding on my part.

I have been tracking interference (cable leaks) on 145.25 MHz also monitor
their test signal on 121.2625 MHz.

Running a dual band Satellite rig ICOM IC-821 with collinear ant around 65'
Sig. strength varies from S3 - S6

IFR attached to 24 element VHF yagi (horizontal) around 45' AGL I find at
least five leak directions with the strongest approx. True North which peers
across the drop point for my home and two other neighbors.  The cable guys
found "A big leak" at this junction yesterday -  One of the other neighbors
drop cable was redone via connector change outs.  After this I still see
about the same sig strength on 145.25 MHz.  Interestingly enough the test
signal strength at 121.2626 is considerable reduced but not the 145.250

145.250 True North = -95dbm on IFR spectrum with yagi. About a 5db

Also I've found a carrier on 110.6125 that peaks in different directions
then the other two frequencies mentioned.  I'm not sure what this if from,
signal peaks at 240 degs -80dbm which is not related to the others as a
source direction.  Only one direction completely nulls with lots of peaks
around the compass.

-----Original Message-----
From: Pete Smith [mailto:n4zr@contesting.com]
Sent: Friday, November 30, 2001 09:37
To: wb3fsr@home.com
Subject: Re: [RFI] RE: Cable Modem RFI/EMI

At 09:08 AM 11/30/01 -0500, you wrote:
...>Selecting any of the three HF antennas (2 r resonate) broad band noise
>quiescent level S9 with peaks of 20db above S9 when tuning the range 1600
>kHz to approx. 5 MHz - Many different signatures that sound like digital
>heard throughout. (9AM this morning)
Peter, for what it's worth I had one instance of really bad modem noise
under the cable drop coming into my yard from the pole.  That was traced
back to a broken shield connection (bad crimp) at the pole.  I'd insist
that the technician pull-test every crimped connector from your modem to
the cable source (whether above ground or otherwise).  He should/will also
have a sniffer with him that is optimized for this job.

73, Pete N4ZR