Around here I also found the Comcast telephone / internet modems
particularly bad. And they generate similar 20 dB over noise floor
noise, with a repetition every 100 kHz or so.
Keep your antenna as far away from it as possible. The Comcast tech
made some measurements, and mostly found it "acceptable" (to whom?!).
He did shorten some of the coax lines leading to the junction box,
and that may have detuned the coax shields from resonance.
When I researched the modems, I found that they use barely any
shielding at all, lots of RF bleeds over the outer shield of the coax
and over the RJ45 network connections. I made the network lines into
chokes by coiling them. Could probably use some good ferrites over
them too. Enclosing the whole thing in a NEMA box would help
enormously. I used aluminum foil one night, but the modem will cook
itself to death with prolonged use.
But what I found most infuriating, apart from Comcasts cavalier
attitude about polluting the RF space, is that the units are made in
China (where else?), and they have a fake FCC certification sticker
on them. Anything for a buck, eh?
Final solution was to move the antennas as far away as possible from
all the Comcast coax lines leading around the outside of the house.
- de Dave, N7AIG
Dr. David McClain
Chief Technical Officer
Refined Audiometrics Laboratory
4391 N. Camino Ferreo
Tucson, AZ 85750
email: d...@refined-audiometrics.com
phone: 1.520.390.3995
web: http://refined-audiometrics.com
On Oct 14, 2010, at 18:06, Steve Sterling wrote:
This has been a good thread-- a couple more sources I lost hair over.
-- those darn touch-on/ touch-off lamps. My wife had about 5 of
those in the house. Down to one. 200khz up to about 60mhz
-- a particular brand of multi-stage battery charger/float
"converter" in the travel trailer or motor home. Its the OEM unit
in 90% of the newer trailers and motor homes sold. It took a major
effort to find, since it was soooo strong, it would break squelch
on my 70cm FM mobile a block away. It just swamped my whole
property. I couldn't find it with signal strength walk-around.
Finally, I tripped all the breakers in the panel, then powered each
circuit up until I came to the 30amp breaker feeding the trailer
power..... ah ha. Replaced with a name-brand unit-- silence was
golden.
-- various consumer wireless routers, port switches, et. al.
Linksys are the worst, but I haven't found any that didn't create
spurs somewhere in the ham bands, clear up through 2 meters.
Replaced my main switch with a Cisco 24 port commercial unit off of
ebay for $60, and a Cisco commercial wireless access port-- end of
those problems.
Not every noise solved, and like others reported, new ones keep
showing up.
On 10/13/2010 8:23 PM, David McKenzie wrote:
Check out this video of the noise I get on 2 meters. It comes up
well over
20 over on some days, and a few weeks ago I heard a football game
on the
carrier. Escalated it to Comcast who is very certain it isn't them
but is
being very helpful in helping me track it down. It's strongest
horizontally,
and it's definitely not coming from here, and is strongest in a
certain
direction as identified by watching it while spinning the beams.
It also
drifts up and down the band but repeats out about 200kHz.
http://www.youtube.com/watch?v=ZKKhySrO5Kw
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