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 d_lBarsoomPremium,MVM
join:2002-12-08
Reno, NV
kudos:7 | reply to Krellan
Re: [Speed Problem] Lost high frequencies over last few weeks Those notches look very evenly spaced which could be caused by harmonic interference, especially the July chart. Have you ever tuned a portable AM radio to the center frequency of some of them to make sure they aren't local AM stations?
Is there any chance your attenuation has increased some, even only by 0.5 dB, since July? | |
Krellan
join:2001-06-06
Castro Valley, CA | Yes, my attenuation has gotten just BARELY worse.
Downstream attenuation:
Back then = 42.5
Now = 43.0
Unfortunately, my SpeedStream modem can't report the upstream attenuation (this is a well-known limitation in the firmware). I can dig out my old Zyxel, which can do this, but it isn't as reliable.
What's killing me is downstream noise margin:
Back then = 7.0 through 8.0
Now = 4.5 through 5.5
Obviously, this is "in the red", as it's below the 6.0 threshhold for minimum acceptable noise margin.
Anything I can do to help fix this?
My DSL wire at the house is rather nice: there's an external splitter next to the NID, and it's Cat 5 from there, all the way around to the DSL modem jack (the DSL side of the wiring has only one jack).
Testing at the NID reveals no difference in quality, between what I have at the DSL modem jack, and what I got when plugging the DSL modem directly into the NID (cutting off voice service at the house). So the post-NID wiring doesn't appear to be a problem. | |
Krellan
join:2001-06-06
Castro Valley, CA | reply to d_l
As for the frequencies of the holes in the graph, I looked them up, and sure enough, they do correspond to major radio stations in this area.
Bin 130 = 560 KHz = KSFO
Bin 158 = 680 KHz = KNBR (Go Giants!)
Bin 189 = 810 KHz = KGO
KGO is a real blowtorch. It's the strongest station in the neighborhood: a friend showed me a homemade crystal radio set that receives all stations simultaneously, as it has no tuner, and KGO is clearly audible above the din.
Interestingly, I live in a valley, that does a good job of blocking radio signals (it makes it hard for me to listen to the radio when I want to). I'm surprised my dropouts in the DSL correspond almost exactly to the frequencies of these major radio stations in the area. My DSL impairment matches the AM radio dial almost exactly: there's a few 50,000 watt monsters near the low end of the dial, then at the high end of the dial, there's so many little small stations that they all disintegrate into noise against each other.
The same friend of mine has a very fancy ham radio set that can take a spectrum analysis of signal strength over a range of frequencies. He lives very close to me, so the radio situation should be fairly similar. I'll ask him to scan the AM radio band, and see what kind of interference there is. It will be interesting to hold up his bandplot, and compare it to my DSL impairment! | |
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