Your scenario is one I've seen a number of times, so experimenting with different power plug arrangements can make a difference.

Hi

Well, if you can design an ADSL modem that can reject AM radio interference and still use the frequencies occupied by that station, then you ought to patent it, because you would make an absolute fortune !

Already done, it's called common mode noise rejection, which is why we use twisted pairs and is how the modem can reject the noise of distance MW radio stations.

I think you would be quite surprised to see just how much power 20 feet of copper wire will pick up from AM radio stations - enough to directly power a pair of headphones with no amplification at all (i.e. a "crystal set").

Which is why telephone cable is twisted pair and common mode noise rejection is used to cancel out the picked up noise. Yes I know all about crystal radio sets, a design to pick up radio waves, ADSL modems are designed to reject them.

I still stand by my opinion that the biggest problem to ADSL is AM radio broadcasting, but what would I know ? I've only been a licensed radio amateur for the last 27 years !

AM radio is a problem, I never said it wasn't. What I was saying is that noise at night isn't due to distant MW radio stations and their signals bouncing hundreds or thousands of miles around the globe. Those signals are very weak and very easily rejected by modern methods used in modems.

Regards

Phil

Edited by deleted (Sun 08-Nov-09 11:24:33)

The causes of this sort of problem are many and various, it can be caused by mains borne interferance, from the phone line itself, a faulty appliance, just about anything. So when dealing it with take a logical approach.

(1) if you can, put the router close to the master socket and use a filter faceplate. this often moves your router away from the rest of your kit and the filter faceplat will help to reduce anything picked up by extension wiring in your home Do try to do this, if only for a few days to see what happens.

(2) Check appliances you use to see if they can provoke the problem.

Interesting; I thought it may just have been some random thing I'd come across.

I don't know if it's an issue with Netgear routers, but they seem very sensitive to very slight power fluctuations. Our lights dimmed briefly the other week (I think the Americans would call that a power brownout!). Nothing was affected, except the router which was bizarrely sort of half-reset as it lost synch but the wireless stayed on.

Hi

Weak distant stations no real issue, nearby powerful ones, it may be just about OK during the day.

People can tell the frequency of stations from the bin plots, which effectively end up in a notched arrangement of bins. Early ANFP docs were concerned about AM radio being affected by ADSL.

I agree and see the same thing, my point was that distant weak radio stations that appear at night are not the main reason for increased noise levels and by design can and are rejected.

Heating pumps not seen those as an issue, but spark igniters and timer relays have been an issue, i.e. people getting a new boiler and not finding out the problem until central heating is on.

Not a good example really I know, I meant that during the night more electrical items are in use especially during the winter. Anything that is electrical is creating some form of noise and the background noise level goes up and we see reduced SNR margin and/or reduced sync speeds. Distant MW radio stations aren't to blame, it's us using all our electrical stuff/

I do wonder what effect the move to energy saving lights is/will have? The humble incandescent bulb doesn't create much in the way of electrical noise I would have thought, but switch all these to high frequency switching compact fluorescent tubes?

Regards

Phil

CFL's have a varying effect, i.e. some cause issues, some dont

In reply to a post by PhilipD:

Already done, it's called common mode noise rejection, which is why we use twisted pairs and is how the modem can reject the noise of distance MW radio stations.

Common mode rejection can stop interference from reaching the modem, but once it's there, the only way that a modem can reject the noise is by not using those frequencies. This will invariably cause a drop in sync speed, because of the reduced number of bins that can be used. Also, the number of twists in the pair are quite low, because a greater number would result in a longer wire length, which would have affects on the attenuation and the capactitance of the cable.

Hi

Common mode rejection can stop interference from reaching the modem, but once it's there, the only way that a modem can reject the noise is by not using those frequencies. This will invariably cause a drop in sync speed, because of the reduced number of bins that can be used. Also, the number of twists in the pair are quite low, because a greater number would result in a longer wire length, which would have affects on the attenuation and the capactitance of the cable.

Wow, for someone who said sarcastically I should patent the idea of common mode noise rejection what a turnaround

The modem will not pick up directly distant radio stations bounding in at night (which is the context of my original post) as it doesn't have an antenna tuned for receiving such signals..

I standby what I said, night time ADSL noise problems being attributed to distant MW radio stations bouncing off the ionosphere is more a myth than the reality.

Regards

Phil

In reply to a post by PhilipD:

Hi
Wow, for someone who said sarcastically I should patent the idea of common mode noise rejection what a turnaround

Oh dear, so you can't read either ?

What I actually said was "if you can design an ADSL modem that can reject AM radio interference and still use the frequencies occupied by that station"

I think maybe you ought to get a printout of all the tones that your router can't use, and match them up with MW radio stations. You may see a link. If a router cannot use a bunch of frequencies, this will reduce the efficiency of the router, especially when the range of frequencies that it is able to use is reduced by the effects of the length of the line. Sure, common mode rejection happening in the twisted pair cable will reduce the amount of interference picked up by the cable, but it won't completely stop it, and at night MW radio signals bouncing off the F layer can be extremely strong.

In reply to a post by PhilipD:

The modem will not pick up directly distant radio stations bounding in at night (which is the context of my original post) as it doesn't have an antenna tuned for receiving such signals..

LOL ! So you don't think a couple of hundred yards of copper cable would make a good antenna ?

Twisted-pair cables were first introduced when newly-installed electric trams were radiating impulse noise into the telephone cables in the 1880's, and twisted pair does also reduce the pickup of wireless signals, but it is nowhere near 100% effective. Sure, a lot of this wiring is underground, but in most installations you will have about 100 metres of overground cable. And guess what 1/4 wavelength of Radio 1 (909kHz) is ?

80 metres. 80 metres of copper wire will give you an excellent radio aerial for Radio 1 AM.

In reply to a post by PhilipD:

I standby what I said, night time ADSL noise problems being attributed to distant MW radio stations bouncing off the ionosphere is more a myth than the reality.

You can stand by what you say for as long as you like, chum, but it doesn't make it correct.

hi,

Have been drawn to post on this thread as all this talk from a poster about "ADSL modems not being tuned to radio stations" is utter rubbish..

Common mode rejection helps.. but it is not infinite.. overhead lines and drop lines are ready antennas for medium wave transmitters.. At night as mentioned these signals are propagated over considerable distances and as the transmitters that send them are usually transmitting megawatts then there is a good chance the signal hitting your line will reach considerable levels , fluctuating of course as various multi path signals from the source arrive in/out of phase etc..

An ADSL modem has no tuning, it is a wideband receiver, it lets in everything in its passband, it receives ALL ! , repeat they have no tuning!.

The ADSL modem on a long line is only receiving signals of -60dBm or less, this is way less than the field strength of a MW station being stormed in via reflection from the atmosphere. Even on short lines the upper frequencies are -60dBm or lower.. this means bins get wiped out and overall SNR takes a dive.

do hope that clarifies. it is no myth.