Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[JGO]

So most Radios built up to about 1965 had a mains transformer as a deliberately built in jammer ? !

[Black Sheep]

The only hum I've heard from a transformer is from the laminated cores ? I'm not into the science as deep as you guys though. 

[sevenlayermuddle]

Mains transformers can generate a 50Hz field that will find its way into audio circuits through simple induction and present itself as 'hum'.  I would not exert that to affect DSL however.

But that is distinct from the situation here, where there appeared to be a well-defined carrier circa 270kHz, modulated by a 'buzzing/hum' sound. 

[NewtronStar]

I'm not into the science as deep as you guys though. 

Yes BS we know, thats why the uk nation as a whole suffers from Interference on the OLD copper part of FTTC and ADSL at some point or another but it was a good effort to keep the price down for the consumer 

[Black Sheep]

So you're saying it was a conspiracy by the GPO to only lay Cu/Ali cables, knowing that DSL was literally just 70yrs around the corner ??

[NewtronStar]

So you're saying it was a conspiracy by the GPO to only lay Cu/Ali cables, knowing that DSL was literally just 70yrs around the corner ??

Sorry BS I keep forgetting how old the GPO infrastucture is, and it's way older than me, how things have changed in the past 17 years we are using the Phone line less for voice communications and using it more for Broadband data communications and still it amazes me how 5000+ kbps can be moved around from one part of the globe to another using two wires 

[NewtronStar]

Mains transformers can generate a 50Hz field that will find its way into audio circuits through simple induction and present itself as 'hum'.  I would not exert that to affect DSL however.

But that is distinct from the situation here, where there appeared to be a well-defined carrier circa 270kHz, modulated by a 'buzzing/hum' sound. 

My Radio Scanner will not go below 300KHZ  the only radio station I can see that transmits at 270KHZ is CZE  Radiozzurnal - Czesky Rozhlas 1
OKA    CZE Uherské Hradisztez-Pre            24H
on LW http://www.dxinfocentre.com/lw.htm

[sevenlayermuddle]

Mains transformers can generate a 50Hz field that will find its way into audio circuits through simple induction and present itself as 'hum'.  I would not exert that to affect DSL however.

But that is distinct from the situation here, where there appeared to be a well-defined carrier circa 270kHz, modulated by a 'buzzing/hum' sound. 

My Radio Scanner will not go below 300KHZ  the only radio station I can see that transmits at 270KHZ is CZE  Radiozzurnal - Czesky Rozhlas 1
OKA    CZE Uherské Hradisztez-Pre            24H
on LW http://www.dxinfocentre.com/lw.htm

Then, if my analysis is correct, they'd better hope nobody in the neighbourhood of any of their listeners ever wants to operate a flood abatement pump that uses powerline comms.   

[JGO]

Sevenlayermuddle,

Thinking  a bit more about it, your explanation seems most plausible since a large 50Hz component wouldn't be acceptable on a system passing any appreciable information rate, either an analogue broadcast station or  data. However for a simple ON/OFF it  could even be part of the system.
If it were the 50Hz power system acting as a spark transmitter, modulated by 50Hz,  (sparks are supposed be due to dirt on insulators and are cleaned off by rain) then the frequency would NOT be closely defined,anything but.

Looking back you don't mention using DSLstats ? Using this on the "Tones" setting is the nearest most of us can get to a spectrum analyser, and would show up 550 kHz and all   harmonics as dips in the tones. 

I would have said that a BT RF3 mode filter should see off any interference (re)radiated from 50Hz wiring and picked up on the 'phone line, but when I tried one, it added attenuation of wanted ADSL tones at low frequency, although it improves things higher up ! 

   

[boost]

burakkucat noted some interference on my QLN around tone 64 that might be related to this?

http://forum.kitz.co.uk/index.php?topic=13931.0

[sevenlayermuddle]

I'm now convinced the flood abatement pumps were the root of the problem.   They have now vanished, and so has the AM radio noise.    It is also worth emphasising that whilst I was fascinated to identify the cause, the impact on DSL was never that bad, just a couple of dB on SNR.   Probably equivalent to living nearby a powerful MW transmitter.

The main symptom was the incredibly strong audible signal on AM radio.   And whereas AM radio noise from, say, a plasma TV tends to vary slighty in pitch and frequency depending on picture content, mine was a rock solid 'hum' on a carrier frequency that never varied.   Obvious, with hindsight, it really had to be some kind of deliberate transmission using the power line as medium.

I do have an RF3 installed, who knows... the impact on my broadband may have been much worse without it?