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Author Topic: Serious interference around 700Khz  (Read 21205 times)

burakkucat

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Re: Serious interference around 700Khz
« Reply #45 on: March 04, 2013, 02:24:22 AM »

That is quite a mystery.  :o 

For both your own and your neighbour's house, do you have any idea of the route the incoming electricity supply cables takes from the street to your respective main fuses? I am wondering if there could be a defect in the electrical distribution cable close to your houses. But that does not account for the observed timing effect.  ???

Perhaps you could interest Walter to trundle his wheel-barrow in your direction . . .  :-X
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Re: Serious interference around 700Khz
« Reply #46 on: March 04, 2013, 08:21:19 AM »

The neighbour shouldn't be on the same phase so if its conducted noise then its coming through neutral (which in theory should be grounded at the substation, but you should never assume it is - many connections aren't grounded).

Example - house #1 will be connected to the red phase; house #2 will be connected to green; house #3 will be connected to blue; house #4 will be connected to red; house #5 will be connected to green etc etc Only earth and neutral will be "common" to all the houses.

I'd be inclined to go for a walk up and down the road checking every third house as they'll be on the same phase. If the noise isn't varying at all (just decreasing) then its unlikely to be conducted emissions and if it is then its more than likely propagating over the neutral wire. Having said that, turning off the mains power at the fusebox doesn't disconnect neutral from the internal wiring so it could be conducted emissions causing the initial problem.

Your last recording sounds like a dodgy ballast (or possibly a wall-wart PSU) to me, so I'd also watch for that and given the hours this happens it may well be external lighting at fault.

Not an easy one to find....
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sheddyian

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Re: Serious interference around 700Khz
« Reply #47 on: March 04, 2013, 11:06:38 AM »

For both your own and your neighbour's house, do you have any idea of the route the incoming electricity supply cables takes from the street to your respective main fuses? I am wondering if there could be a defect in the electrical distribution cable close to your houses. But that does not account for the observed timing effect.  ???

The timing effect is the killer here.  Sunday evening seems to be problematic.  But why?

The neighbours attend church on a Sunday, and also don't watch TV on a Sunday, but DO play an electric organ (the husband plays organ in the church they attend as well).   Potential pattern match there - different behaviours on the day I get interference!

BUT

It seems to start when they're out at Church in the evening.

Wandering around their house with a radio couldn't pinpoint it's source

Switching off ALL their electric didn't silence it.

I will keep the radio switched on a lot more, and see if it comes back (perhaps at reduced strength) at other times.

Sunday evening seems to be the day to lose synch, but I have seen higher (but not drastic) error levels during the week as well.

And just to recap, this recording from Sunday 24th February is the noise I was hearing yesterday (Sunday 3rd March) http://sheddyian.hopto.org/interference3.mp3 across most of the lower end of the MW band, certainly on/around 612kHz.

The interference was so strong in the neighbours house that I couldn't find Radio 5 Live, which usually comes in strong around here!

Ian
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Black Sheep

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Re: Serious interference around 700Khz
« Reply #48 on: March 04, 2013, 11:24:56 AM »

If you've switched off ALL the electric at the mains board, then it can't be emanating from your neighbours house and you're wasting precious time.

Haven't time to read back through this thread, but are you fed Overhead, or Underground ??
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sheddyian

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Re: Serious interference around 700Khz
« Reply #49 on: March 04, 2013, 11:45:59 AM »

If you've switched off ALL the electric at the mains board, then it can't be emanating from your neighbours house and you're wasting precious time.

Haven't time to read back through this thread, but are you fed Overhead, or Underground ??

My last post wasn't very clear, I'd intended it to be a "here's the oddity of it" - they appear to be prime suspects with significantly different behaviour on the day the noise appears, and it being very strong in their house YET it can't be them because switching their mains off didn't silence the noise even slightly. 

So, yes, I have ruled them out.

The phone wires are underground all the way, excepting the last 2 metres which runs up the wall in the middle of our semi-detached to an external grey junction box.  This feeds us and immediate neighbour.  (this is different neighbour to  the one I thought the noise came from).  When present, noise is quietest on this side of the house.

Mains electric also comes in underground, also on front of house but on other side.

Have quickly scribbled a plan, in case it's of any help to understanding what's going on.

Ian
« Last Edit: March 04, 2013, 12:01:48 PM by sheddyian »
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asbokid

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Re: Serious interference around 700Khz
« Reply #50 on: March 04, 2013, 12:14:02 PM »

Probably a silly question, but how have you eliminated Neighbour #1 and Neighbour #4 from being the cause?

« Last Edit: March 04, 2013, 12:32:02 PM by asbokid »
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Re: Serious interference around 700Khz
« Reply #51 on: March 04, 2013, 12:15:41 PM »

If you've switched off ALL the electric at the mains board, then it can't be emanating from your neighbours house and you're wasting precious time.

Mmmm not quite.

Do they have an alarm system? The thought occurs as there seems to be a corrrelation between them being "out" on Sundays and the problem occurring.
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Black Sheep

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Re: Serious interference around 700Khz
« Reply #52 on: March 04, 2013, 12:38:23 PM »

If you've switched off ALL the electric at the mains board, then it can't be emanating from your neighbours house and you're wasting precious time.

Mmmm not quite.

Do they have an alarm system? The thought occurs as there seems to be a corrrelation between them being "out" on Sundays and the problem occurring.

If i'm reading this right (and I often don't  ;D), Ian has switched off all the electric at the mains (in the neighbours house), and the noise is still present ?? Whether the alarm is set or unset with the electric back on, it shouldn't play a part, as the noise is there regardless ?
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guest

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Re: Serious interference around 700Khz
« Reply #53 on: March 04, 2013, 12:56:11 PM »

The alarm panel will be battery backed up so killing the power will have no effect on it at all - if its generating noise then the noise will still be present whether mains is on or off.

I doubt that's it but the cabling on alarms is just bellwire and generally about the right length to radiate MW/HF. There's all sorts of different sensors as well - we have dual PIR/microwave sensors but the microwave element of the sensor is only turned on when the alarm is set - so there's plenty of potential for issues.

The only time correlation Ian has managed to make is when the neighbours are off out godbothering so maybe worth a try.
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sheddyian

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Re: Serious interference around 700Khz
« Reply #54 on: March 04, 2013, 01:14:10 PM »

Probably a silly question, but how have you eliminated Neighbour #1 and Neighbour #4 from being the cause?

I haven't directly eliminated them, no, because the apparent centre of the noise was either myself or neighbour "3".

Neighbour "3" doesn't have an alarm, and aside from a programmable thermostat for their heating which seemed to be battery powered, I can't see anything else that might be making noise without mains power.  The stat made no noise, with or without power!

The noise was a lot quieter around "1" and "4".

HOWEVER

I've just been round to neighbour "3" for a chat, and took my radio to demonstrate that the noise was gone today.

Or, as it turns out, gone in my house, but still present in theirs, albeit quieter than last night. 

And the strongest source is their party wall with "4".  If I go into "3"'s garden, hold the radio close to the house and the party wall, it's worst in that corner (back corner, farthest from road).

So it looks like it could be coming from "4".

A walk around the block shows that I can't detect it at all from outside, only in "3"'s house where it adjoins "4"

But it's odd that last night the strongest point appeared to be centred between "2" and "3".  Now it's between "3" and "4".

How could this be?

I don't know the people at "4" at all, so I've go to play this carefully so I don't look mad, turning up on their doorstep asking if I can walk around their house listening to noise on my radio....  ???

Ian
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sheddyian

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Re: Serious interference around 700Khz
« Reply #55 on: March 04, 2013, 01:18:51 PM »

If i'm reading this right (and I often don't  ;D), Ian has switched off all the electric at the mains (in the neighbours house), and the noise is still present

Yes, that's right. Switching off mains in my house "2" and neighbour house "3" does nothing to silence or even reduce the noise heard on the AM radio when it's present.

However, my suspicions are now on house "4" which seems to be emanating the same noise, though at reduced intensity compared with last night.

Ian
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burakkucat

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Re: Serious interference around 700Khz
« Reply #56 on: March 04, 2013, 06:38:31 PM »

Having said that, turning off the mains power at the fusebox doesn't disconnect neutral from the internal wiring so it could be conducted emissions causing the initial problem.

I thought that all main switches were double-pole?  ???
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sheddyian

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Re: Serious interference around 700Khz
« Reply #57 on: March 04, 2013, 07:11:06 PM »

Having said that, turning off the mains power at the fusebox doesn't disconnect neutral from the internal wiring so it could be conducted emissions causing the initial problem.

I thought that all main switches were double-pole?  ???

Good point there - I'm pretty sure they are, as the incoming Live & Neutral from the meter go straight to the main switch.

As an aside, I think all but the cheapest switched mains sockets are double pole too.

Ian
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Re: Serious interference around 700Khz
« Reply #58 on: March 04, 2013, 07:32:17 PM »

Having said that, turning off the mains power at the fusebox doesn't disconnect neutral from the internal wiring so it could be conducted emissions causing the initial problem.

I thought that all main switches were double-pole?  ???

Why would you think that?

The way this is supposed to work in the UK is that you fuse live and RCD earth in the premises. You fuse live at the tails on the meter.

Edit - to clarify, the only current path to neutral/earth is via the fused/switched live side so why would you expect switches that isolate neutral?
« Last Edit: March 04, 2013, 07:35:16 PM by rizla »
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Black Sheep

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Re: Serious interference around 700Khz
« Reply #59 on: March 04, 2013, 07:50:56 PM »

All modern split-board consumer units, should use the 100Amp double-pole breaker.
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