In article ,
Jim Leder wrote:

After several months of just not listening to my 2 meter base station, I
finally took time to find the source of the interference that held the
squelch open on the repeater channel I listen to most often. Turned out it
was my Dlink DI-604 router. I borrowed a Linksys NR-041 router from my
neighbor and it works a little better. I can now listen to the 145.390
repeater, not because the Linksys puts out no RFI, but only because it puts
it out in a different place (mostly in the 146.46-146.58 range). I will
probably invest in a newer router, probably wireless. Question I have is
does anyone have any experience with the new breed of wireless routers that
are reasonable clean in the RFI/2 meter spectrum? Thanks.

Back in August I helped my city's ARES/RACES EC chase down a 2-meter
interference problem at his condo. An HP spectrum analyzer showed a
whole series of regularly-spaced spurs throughout the 2-meter band -
most strong enough to de-squelch an HT, and several strong enough to
compete with repeater-output signals on the same or nearby frequencies
and make communication difficult or impossible. He had the usual
"cable channel 18" spur on 145.250 (not a new problem at his QTH) but
the multiple spurs were something new.

By plugging a measuring-tape Yagi-Uda foxhunt antenna into the spectrum
analyzer, we quickly localized the source of the signal to the
neighboring condo unit, second floor, rear of the building, polarized
45 degrees from vertical :-)

He spoke with his neighbor, and they quickly identified the neighbor's
new Netgear 802.11b/g WAP/router/switch as the cause. We did some
RF-snooping with the spectrum analyzer and a rubber duck, and
determined that the spurs were radiating from within the router's case
itself. The source seemed to be on the right side of the case, just
in front of the DC power inlet jack. There was no significant spur
radiation from the power cord itself - it was coming from the PC
board, and whatever ferrites or whatever Netgear had put on the DC
inlet were doing their job just fine.

My conclusion was that the Netgear model in question uses a buck-mode
switching voltage regulator, operating at a switching frequency of
about 30-40 kHz (the spacing of the spurs we saw), and that its
internal switch generates very fast current rise/fall times which
radiate harmonics from the PC board.

I ran a similar test on an older model of Netgear wireless router (one
of a couple I'd picked up at a swap meet) and observed no such
problem. The older router's switcher does emit some low-level 2-meter
hash into a nearby probe, but it's much less energetic and appears as
broadband RF noise with no significant peaks. Possibly the older unit
has a spectrum-spreading feature in its regulator, or possibly it's
just a better design RF-wise (slower switching edges, self-shielding
inductors, better grounding/routing on the board, etc.).

The noisy router is a Netgear model WGR614 v6 (802.11b/g), FCC ID
PY305100002.

The non-noisy one is a Netgear model MR814 v2 (802.11b), FCC ID
PY3MR814v2.

My EC's neighbor (a retired EE who takes Part 15 quite seriously) went
out and bought a different model of b/g router, and the problem went
away. I'm afraid I don't know the number of the replacement model.

Given how frequently manufacturers revise their hardware (every time
their OEM gets a new batch of parts, I suspect) I think you're
probably going to have to test individual models for acceptable QRM
levels. A model number which looks OK today, might or might not have
the same guts in it as a unit of the same model number that you buy
three months from now.

A year or so before that, a few other guys and I used the same HP
spectrum analyzer to locate the source of some QRM which was causing a
buzzing squelch-tail interference on numerous local 2-meter repeaters.
It turned out to be a Netgear 4-port wired-Ethernet hub, which was
howling like a whole chorus of dire wolves on a high-order harmonic of
its (drifty) internal crystal's frequency. The signal was apparently
getting into all of the 10BaseT wiring and back out the power cord
into the mains... his whole apartment was radiating. From a block
away we could "see" when the owner started to download files from the
Internet, thanks to the strong pulsing spur which would appear
somewhere in the 2-meter band.

I offered him one of my spare 6-port hubs (an Airlink) in return for
his defective unit, he agreed, we made the exchange. Problem solved,
hasn't returned.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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