'Normal' SNR evening drop?

Hi everyone,

Was just wondering what magnitude of decrease in SNR margin most people see due the various factors at play during the evening? My line now has a traget SNR margin of 15db and sits rock solid at that all day long. Once the evening begins it starts to jump all over the place and will always eventually go negative and force a resync. Is a drop of over 15db from optimum daytime performance to be expected or could something be wrong somewhere?

Thanks

Edited by thompsbd (Tue 06-Mar-07 23:21:23)

It sounds like your internal wiring may be prone to noise pickup, I rarely see more than a 5db swing during the night hours. How is your router connected, eg at the master socket, via a hard-wired extension or using a 'flying lead' extension?

Internal wiring is the main culprit, but some lines are more badly affected than others. I have 2 ADSL lines here - one line is much worse than the other (ironically the one with the better attenuation figure), and the lines take an identical route - the only difference is that the line with the worse SNR and SNR drift is about 12 feet longer than the other (one master socket is in one of the bedrooms, and the other is in the lounge).

My router is connected using a short shielded RJ11 cable to a filtered faceplate on the master socket. Strange thing is that I have a second line into the house (along the same physical cable) which isn't experiencing similar SNR drops. It has a target SNR of 6db and hasn't resynced for ages. I'm struggling to identify anything my end which could be causing it.

Brian

I have a similar drop and have tried all the usual suggestions including ferrite rings and two stage UPS and they make absolutely no difference whatsoever. The problem is external. The initial sync in the morning when I turn the router on gives around 4500 which would give a profile of 3.5mb which I sometimes have, however I have been trying different things and have found if I sync around 3700 the line will not drop but of course with a lower 3mb profile. It depends whether you need the extra speed or just want a stable line.

Ferrite rings are of no use whatsoever. The problem is that the wanted and unwanted signals are the same frequency, and ferrite rings will attenuate both the wanted and unwanted signals.

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Ferrite rings are of no use whatsoever. The problem is that the wanted and unwanted signals are the same frequency, and ferrite rings will attenuate both the wanted and unwanted signals.

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I have put them on the power leads not the adsl leads, the idea being to remove AM frequency noise picked up via the overhead and other wires. I am on a very rural site all our power is via overhead wires.

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I am on a very rural site all our power is via overhead wires.

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Same here, but the inductance of the electricity meter usually takes out these frequencies, which is why Home Plug won't work between houses.

My old house used to see a 10db drop in the evenings most of the time. New location moves probably about 2db if that. Both on the same exchange

Old location, lots of lights further from the exchange, new one hardly any lights, very close to the exchange.

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Same here, but the inductance of the electricity meter usually takes out these frequencies

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That interesting, I had not heard of that before. Our meter is 180 mtrs away

Where electricity is fed via overground wires, the telephone lines are usually overhead too. Removing noise from electric cables is relatively easy, because the mains is 50Hz, and you just filter everything above 50Hz (ish). The problem with ADSL on phone lines is that the interference and the wanted signals both look very similar, so it's impossible to filter out the unwanted from the wanted.

Home plug will not work between adjacent houses because they are almost certainly on a different phase and thus do not have a common live connection. Every third house may receive teh signal but it is likely to be attenuated by distance.

As every socket in the house returns to a common point between consumer unit and meter, the filtering effect you mention would affect connections within the house as it will be presenting a low impedance path for the higher frequencies very close to teh common point and would thus attenuate the signals.

Not true. The attenuation of the HF signals would be due to the effect of the meter acting as a choke in series with the live feed. You may recall that a system which relied on ADSL delivery via mains wiring had to have a box installed in each house, because the ADSL signals would not reliably pass through the electricity meter.

P.S. The practice of wiring "every third house" is not carried out too much these days, because it is dangerous (nearly 500V between lives in adjacent premises is not a good idea when satellite dishes can be 2 feet apart). It is only done to even the load, and this is now achieved by wiring blocks of premises, and rarely done to single dwellings any more.

Edited by deleted (Fri 09-Mar-07 09:54:10)

I was having similar problems with my snr dropping to minus figures every eve between 5.30 and about 8, Idnet my isp did all kinds of test's etc .
I decided to change my internal wiring I fitted an adsl nation pre filtered faceplate and a adsl 2+ rj11 lead . The snr has not dropped since and am synced at 8128 so that seemed to cure my problems may be worth a try cost me