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Author Topic: Serious interference around 700Khz  (Read 26720 times)

roseway

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Re: Serious interference around 700Khz
« Reply #15 on: February 19, 2013, 10:07:27 AM »

If you look at MW channels in the UK you can see that 612kHz is fairly well removed from any UK transmitter frequencies. I guess that there's a degree of arbitrariness in the choice of that particular frequency, but it's not a bad choice.
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JGO

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Re: Serious interference around 700Khz
« Reply #16 on: February 19, 2013, 11:17:59 AM »

" It's not 'special', it's just the frequency our Chief Engineers Office recommend. I believe it's due to there not being much else around that particular frequency to cause disruption. However, one can hear a (I think it is) French radio station until approx. 0830 in a morning."

OK.  I agree it is quite a good choice, but the general impression is that there IS something special, which suggests that ADSL works in some unique way.  As to  "Chief Engineers Office recommend",  someone once told me of a Chief Engineers Office approved design which involved drilling a 1" diameter hole in a 1/2" strip ! 
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sheddyian

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Re: Serious interference around 700Khz
« Reply #17 on: February 19, 2013, 11:43:48 AM »


It seems to me that the choice of 612kHz as a frequency to detect REIN on is a bit arbitrary, given that ADSL uses frequencies from 25kHz up to 2200kHz.

In it's favour are (as pointed out) it's a generally quiet frequency with no UK stations on, and it's at the lower end of the spectrum where everyone will have some ADSL signal, regardless of line length or ADSL technology.

Maybe it's also got some harmonics further up that are relevant too?

I'm not disagreeing with the choice, if you've got to have a "standard", that one seems good.  And now I know what it is, I'll be using it in future.  Yesterday I just had a vague remembering that it was the lower end of the MW scale that was important, hence tuning around that end until I found noise, and trying to find where it came from.

And, interestingly, my radio dial appears to be misaligned a fair bit...  I tried a different radio earlier, which has a quite basic digital display of the frequency.  And discovered that I'd tuned my original radio far nearer to 612kHz than the 700kHz I thought it was on!  :D

Update on the original problem : with the 'rogue' PC unplugged since early evening, I've had no ADSL disconnections or resynchs since, and the error seconds are currently showing as 375 after 18 1/4 hours of uptime, which I make as an average of 0.34 errors per minute.

Sadly the modem doesn't tell me error seconds in last hour or other divisions, just an overall total.

I've now ordered a new PSU for the PC  ;)

Ian
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Black Sheep

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Re: Serious interference around 700Khz
« Reply #18 on: February 19, 2013, 12:24:30 PM »

" It's not 'special', it's just the frequency our Chief Engineers Office recommend. I believe it's due to there not being much else around that particular frequency to cause disruption. However, one can hear a (I think it is) French radio station until approx. 0830 in a morning."

OK.  I agree it is quite a good choice, but the general impression is that there IS something special, which suggests that ADSL works in some unique way.  As to  "Chief Engineers Office recommend",  someone once told me of a Chief Engineers Office approved design which involved drilling a 1" diameter hole in a 1/2" strip !

Life's full of misquoted urban myths, JGO. Someone once told me that their Uncles deceased pet dog, contacted them to say Elvis was indeed driving a red London bus, on the moon. As regards this particular 'ChEO' advice, it's listed in all our official documents and compiled by people with lots of letters after their name, who spend all their time working on these issues.

I'd say it's more than just "a good choice".  ;) ;D
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Ezzer

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Re: Serious interference around 700Khz
« Reply #19 on: February 19, 2013, 05:15:26 PM »

If thats the same French station I always picked up then it's at 624kHz It can be handy as a rough calibration for your radio.

612kHz is the next harmonic up from the key frequency near 300khz from which DSL has its foundation. Interfere with that and you'll really upset your DSL signal.

(MW radios don't go down as far as 306Khz so you make do with the next harmonic)

Each harmonic up has an effect although the magnitude reduces the further away from. It works much like musical notes; harmonics, semi tones etc. Be it sound, light, or electro magnetic.

Using the 444b is like using a radio, but the 444b broadcasts a wide range of radio frquencies all at the same time, unlike a typical radio where you concentrate on one (with a little bit of signal either side)

But tracking down a noise at a different frequency you are opening up yourself to chasing red herrings. Yes what you pick up @ 700kHz could well be having an effect on your DSL. ALthough the type of noise makes a difference as well. It's like having a conversation with some one and there is backround noise. Some noises are really distracting and throw your conversation off completely. Some noises seem to have little distraction. Although it would still be a little easyer without it.

DSL is the same, if the noise is similar to the digital signal of dsl then it has a greater effect on your speeds. This is why dsl still works dispite so much emf around us.

If it back feeds down the mains then you tend to get the noise popping up everywhere. The source could be anywhere in the noisy reigion, not just the centre. Switching fuses off on your consumerboard one by one may help in working out which group of items could be the suspect


Looks like you are finding out what locating a REIN fault is like. And why most engineers seem to run from tackling REIN. The 444b seems to be looked apon like a poison chalace.

You have to think back to your old school physics days, think about how magnatism forms around wires (hence radio waves) Think about the type of noise signal, in comparison to a dsl signal (the hissing noise you heard, Hold the radio by the router or phone cable to get an idea what it sounds like. Tune your car radio to 612kHz and you'll hear it each time you drive under a drop wire with DSL)

And think of all this EMF like an orchestra. Harmonies, but in electronics harmonies can be the opposite of making good music.
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Black Sheep

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Re: Serious interference around 700Khz
« Reply #20 on: February 19, 2013, 08:52:09 PM »

Great info, Ezz.  :)
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burakkucat

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Re: Serious interference around 700Khz
« Reply #21 on: February 20, 2013, 12:54:10 AM »

A few quick comments from The Cattery:
  • The 2Wire 2700HGV and 2701HG-C devices actually quote the Downstream attenuation at 300 kHz: X.Y dB on their statistics pages.
  • I use an ICOM IC-R5 as my receiver of choice for REIN investigations. With the squelch wide open, I will first check on 612 kHz and then repeat the sweep on 300 kHz.
  • The noisiest switching mode PSUs that I have ever discovered are the white-cased, BT-branded ones that come with the Huawei HG612 modems, type 3B, supplied by Openreach as the active CPE for their GEA product!
  • The quietest switching mode PSUs of the many that I have examined are the genuine 2Wire devices for the 2700HGV modem/routers. (A.k.a. the type 1 & type 2 BT Business Hub, Version 2.)
(Edited to insert the forgotten parameter that the 2Wire devices report -- having just powered one up to check.  ;)  )
« Last Edit: February 20, 2013, 06:16:28 PM by burakkucat »
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sheddyian

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Re: Serious interference around 700Khz
« Reply #22 on: February 20, 2013, 11:07:05 AM »

All fascinating, thank you  :)

Quick update : since disconnecting the noisy PC, I've had 42 hours of uninterrupted connection, with a total of 811 errored seconds.  During the peak of the fault, it would usually lose synch several times in an evening, so this is looking good.

burakkucat : I've used a very ordinary MW radio before to detect interference, and found various switch mode PSUs making noise, but only in their near vicinity.  This noise was something else entirely, to be heard at the same level anywhere in the house as I walked around with the radio, only fading when I went outside, then increasing again as I went into the shed.

Given that unplugging LAN cables from switches would partially silence it, and I could also silence it in the shed by disconnecting the mains feed to that building, it seems it was being radiated through the LAN and the ring main.

Wonder if it was affecting the neighbour's ADSL ?  :-[

I tried to make a recording of the noise on my phone, but I've not checked if it worked yet.  If it did, I'll upload a recording later, if anyone might want to hear it  :D

Ian
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burakkucat

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Re: Serious interference around 700Khz
« Reply #23 on: February 20, 2013, 11:19:54 AM »

Given that unplugging LAN cables from switches would partially silence it, and I could also silence it in the shed by disconnecting the mains feed to that building, it seems it was being radiated through the LAN and the ring main.

Yes, I agree. It clearly had two methods to propogate.

Quote
Wonder if it was affecting the neighbour's ADSL ?  :-[

Well, it isn't, now!  :-X

Quote
I tried to make a recording of the noise on my phone, but I've not checked if it worked yet.  If it did, I'll upload a recording later, if anyone might want to hear it  :D

Yes, please.

I just wish I had some means of recording the noise radiated from that Beattie branded PSU. It was quite distinctive, pulsing at approximately 2 Hz.
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sheddyian

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Re: Serious interference around 700Khz
« Reply #24 on: February 20, 2013, 12:10:40 PM »

Okay, I have recordings!

The first one was recorded whilst I was still trying to determine where the noise was coming from.  I set the radio on the other side of the room to one of my Gigabit Ethernet switches.

The noise was to be found across a reasonable sweep of the bottom end of the AM radio dial. I believed the peak to be around 700kHz but now realise the dial is inaccurate, and it's a lot nearer to the magic 612kHz than I first thought.

The noise was very loud, tuning the radio to a pop music station, the music was quieter than the interference.

The pulsing sound you hear coincides with activity lights flashing on the switch, this is why I at first thought the switch or it's own PSU was to blame. 

The pulsing is actually a dropping away of the noise, which is otherwise constant.

As you listen to the recording, you'll hear the pulsing stop - this is because I am at this point unplugging the Ethernet cables from the switch.  I then try powering down the switch, but the noise remains constant.

There is one point where the sound fades away, this was either me retuning the radio or moving the mobile phone I was using to record the radio as I repositioned it.

I eventually tracked the noise down to a rogue Dell PC downstairs, which was switched off but plugged in to the mains, so the PSU was still "live".

The second recording is one I have just made, to show how that same frequency sounds with the rogue PC unplugged from the mains.  Although it sounds as loud as the first, in actual fact I have turned the radio volume up full as I was concerned the sounds wouldn't be heard, they are MUCH quieter than the interference was.  To me this now just sounds like typical AM static.

http://sheddyian.hopto.org/interference1.mp3 < Interference 1 (This was heard all around the house)
http://sheddyian.hopto.org/interference2.mp3 < Interference 2 (AM silence once the rogue PC was disconnected!)

Ian
« Last Edit: February 20, 2013, 04:05:33 PM by sheddyian »
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Ezzer

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Re: Serious interference around 700Khz
« Reply #25 on: February 20, 2013, 03:52:11 PM »

The first one I've heard before and yes I would say DSL would be affected.

Similar to the noise from some flat screen monitors (one of the most common culprits I found) But usually continuos. The stuttering... I've heard this exact noise before, but its driving me mad as to where and what it was. :wall:

 You're right about REIN greatest hits. This tune is the type that is in your head and you go mad trying to remember the artist

Sounds like some appliance plugged into the mains thats back feeding the noise into a ring all right.

I would look to switch each ring off at the consumer board one at a time to see which causes the noise to stop then go along each item connected to that ring one by one, switching off and disconnecting.

The second noise is a bit hit and miss as to wether it would effect DSl. I've often heard similar without it  making any difference.
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sheddyian

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Re: Serious interference around 700Khz
« Reply #26 on: February 20, 2013, 04:03:41 PM »

The first one I've heard before and yes I would say DSL would be affected.

Similar to the noise from some flat screen monitors (one of the most common culprits I found) But usually continuos. The stuttering... I've heard this exact noise before, but its driving me mad as to where and what it was. :wall:

 You're right about REIN greatest hits. This tune is the type that is in your head and you go mad trying to remember the artist

Sounds like some appliance plugged into the mains thats back feeding the noise into a ring all right.

I would look to switch each ring off at the consumer board one at a time to see which causes the noise to stop then go along each item connected to that ring one by one, switching off and disconnecting.

The second noise is a bit hit and miss as to wether it would effect DSl. I've often heard similar without it  making any difference.

The pulsing noise corresponded to the activity lights on the ethernet switch, so I think that was somehow modulating the interference.  Disconnecting the switch from the mains stopped the pulsing, and the noise became continuous.

The source of the noise is a Dell Dimension 5100, when it's unplugged from the mains, the noise goes away.  This is repeatable, so I'm confident it's the problem.  I've ordered a new PSU for it now.

The second "noise" isn't really noise as far as I'm concerned, it's just a loud recording of AM background static really - I recorded it only to demonstrate a "before" and "after".  Now that the Dell PC is disconnected (but everything else is powered as before, including the Ethernet switch that had been modulating the sound), the loud noise has gone away and the ADSL has remained in synch for 47 hours and counting.


Ian
« Last Edit: February 20, 2013, 07:47:14 PM by sheddyian »
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Ezzer

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Re: Serious interference around 700Khz
« Reply #27 on: February 20, 2013, 05:16:43 PM »

Thank you, Now I remember, it was a Netgear ethernet switch, 16 ports I think. Noise and stuttering. Once you mentioned the ethernet ports it came back. I'm sure it was that one.

Been going round East Anglia in my mind trying to remember

Now what's that  1982-83 tune is that that Lilly Allen lifted ? :hmm:
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burakkucat

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Re: Serious interference around 700Khz
« Reply #28 on: February 20, 2013, 06:28:05 PM »

Okay, I have recordings!
<snip>
http://sheddyian.hopto.org/interference1.mp3 < Interference 1 (This was heard all around the house)
http://sheddyian.hopto.org/interference2.mp3 < Interference 2 (AM silence once the rogue PC was disconnected!)

Very interesting to hear. Thank you. I must admit that I have never come across 'modulated' REIN, as in your first example, so that is something new for me to remember.
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sheddyian

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Re: Serious interference around 700Khz
« Reply #29 on: February 21, 2013, 07:02:20 PM »

Quick follow-up :

New ATX PSU arrived today, fitted it to the rogue PC.

PC working fine (though it was never exhibiting any problems itself), but more importantly.. radio tuned to 612kHz AM just gives me occasional distant foreign station fading in and out.  Tuning up to 700kHz is equally noise free.

Sorted!

Anyone want to buy a used ATX PSU?  Working order, many hidden features, sold as seen  ;D


Ian
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