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Old 27th Jul 2019, 3:56 pm   #1
The Philpott
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Default (Another) MW/LW interference problem

On testing an old car radio with an improvised antenna i have encountered a regular and consistent 'bzzt-bzzt-bzzt' interference across most of the MW band, highest at 1000Kc/s. It is also appearing on LW at around 280Kc/s.
I blamed the test rig set-up, until i tried another radio and encountered the same regular pulse.

Having moved away from the workshop, up the garden and into the house, the intensity remains more or less the same- it therefore looks like it is a reasonably powerful signal, and somewhat distant from the receiver.

At least it shows the radio is working, but what a pain! Any ideas?

Dave
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Old 27th Jul 2019, 5:13 pm   #2
Mike. Watterson
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Default Re: (Another) MW/LW interference problem

Complain to Ofcom.

I complained to Comreg and it took a YEAR. Faulty SMPSU in next door's HDTV.

There is NO in market validation that products meet CE. What is imported often has less or no filtering compared to what was submitted for CE test. The main culprit is National Regulators only interested in collecting revenue from Telecoms operators, not the EU.

There is though an issue with how power line Ethernet and PSUs /Ballasts on LED and CFL lamps are tested. Also self certification.

Could be anything from a Cattle Fencer to a satellite box SMPSU using the external coax to radiate.

Or even the car electronics. The Electronics on my 2008 Diesel car generates more RFI making R4LW barely usable than the ignition did on my 2000 Petrol car!
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Old 27th Jul 2019, 6:03 pm   #3
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Default Re: (Another) MW/LW interference problem

Are there any solar panels nearby?

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Old 27th Jul 2019, 7:05 pm   #4
The Philpott
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Default Re: (Another) MW/LW interference problem

No solar panels close by, as all gable-ends are north-south aligned in this road.
Not vehicular interference as it was on the test bench.
I will try it at different times to see if it's an appliance that's in intermittent use.

Thinking about it the car radio i have in use has MW and LW ranges, so it might be a case of driving around Gestapo style to see how localised the effect is.

I might even have to enlist Guy's help to triangulate it next time he's in the area!..

Thanks for your suggestions.

Dave
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Old 27th Jul 2019, 8:43 pm   #5
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Default Re: (Another) MW/LW interference problem

Can you null it out or establish a direction on a set with a ferrrite rod aerial?
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Old 27th Jul 2019, 9:53 pm   #6
The Philpott
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Default Re: (Another) MW/LW interference problem

A cunning plan. I should find my smallest transistor set, ready for when the rain stops. I got blamed for GENERATING the noise earlier on. I had to explain that I was receiving it.. Such is life.

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Old 27th Jul 2019, 11:11 pm   #7
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Default Re: (Another) MW/LW interference problem

Quote:
Originally Posted by The Philpott View Post
A cunning plan. I should find my smallest transistor set, ready for when the rain stops.
And that's another thing... Is the interference weather-dependent? Do you have overhead rural distribution electricity supplies or is it all underground?
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Old 27th Jul 2019, 11:18 pm   #8
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Default Re: (Another) MW/LW interference problem

Have you tried it in a place well away from phones?
This applies to both masts and hand sets.
I have often heard those noises when there is a phone close to almost anything with a bit of gain.
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Old 27th Jul 2019, 11:46 pm   #9
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Default Re: (Another) MW/LW interference problem

Only just detected this interference today, so not sure if weather dependent. No phone in the workshop, mobile,cordless or otherwise. Power cables are underground. Nearest 11kv transformer is some distance away (if that's at all relevant.)
There are no booster masts in the immediate vicinity.

The signal is sufficiently strong that i don't think it will remain anonymous for long.
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Old 28th Jul 2019, 8:21 am   #10
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Default Re: (Another) MW/LW interference problem

Stupid question, but, you or your neighbour have not just installed plug in adaptors to carry ethernet signal over the mains have you?
I started using these to get the internet down the garden to the workshop as I did not want to run cat 5/cat6 cables down there.
I then had the same 'bzzt-bzzt-bzzt' interference everywhere, I even saw it on my scope when testing audio.
I got rid of those plug in units, they send data by sending rf at frequencies up to 30MHz down the mains. Inventions of the devil as far as I am concerned (rant over).

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Old 28th Jul 2019, 10:48 am   #11
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Default Re: (Another) MW/LW interference problem

My workshop is in the loft and I have horendous interference on AM....it makes most radios unusable up there. Move them downstairs and its a different story. Now there are a few things that I have that cause some very localised interference....move a foot or two away and there is no problem. The main problem seems to be my neighbour's security system which uses the internet for communication and also over mains for some other things. I have no arguments with my neighbour so I'm trying to improve the situation in my 'den'. I'm fitting mains filters and next I'll sort out a better aerial system to try and screen the worst of the interference out.

Why is it confined to the loft area?......because that is where all his power supplies and ethernet stuff is.

Alternatively I need to move my workshop downstairs.......!
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Old 28th Jul 2019, 11:17 am   #12
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Default Re: (Another) MW/LW interference problem

No, just a Plusnet unit (the only socket on the rear that is in use is the broadband DSL port)

I have switched the power off at the consumer unit. Whatever the source is, it's in the house. On powering it back up the pulse bzzt-bzzt effect has now become a constant buzz.
Repeating procedure and seeing what happens.
Dave
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Old 28th Jul 2019, 12:18 pm   #13
The Philpott
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Default Re: (Another) MW/LW interference problem

It was the power supply for a (long redundant) stannah stairlift!
Thanks for your suggestions.
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Old 28th Jul 2019, 2:37 pm   #14
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Default Re: (Another) MW/LW interference problem

My old central heating controller (well more correctly the heating/hot water controller generated a significant amount of interference. It was a while before I discovered it and it was only when I heard the heating click on that the interference increased. I thought initially it was the pump but that operates with heating and hot water. I changed the controller for a much later model.....problem solved.
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Old 28th Jul 2019, 2:51 pm   #15
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Default Re: (Another) MW/LW interference problem

Oh drat!! You've solved the mystery!

And it was just getting intriguing too.....
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Old 28th Jul 2019, 6:08 pm   #16
The Philpott
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Default Re: (Another) MW/LW interference problem

Bearing in mind the change in the interference following power interruption i will be opening up the power supply when i get time- sounds like it needs attention should it ever need to be used again!
Dave
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Old 29th Jul 2019, 9:43 am   #17
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Default Re: (Another) MW/LW interference problem

Hi Dave - really pleased that you managed to find the source of the interference.

From recent experience I fully understand how frustrating these issues can be.

See my Post #70 here: -

https://www.vintage-radio.net/forum/...=146402&page=4

And my Post #85 here: -

https://www.vintage-radio.net/forum/...=146402&page=5
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Old 29th Jul 2019, 5:45 pm   #18
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Default Re: (Another) MW/LW interference problem

Aside from the well-known problem of cheapskate suppliers omitting suppression components from circuit boards (after self-certifying compliance with them fitted to the prototype), I wonder if some of these problems are caused by gradual deterioration of X, and possibly Y, capacitors?
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Old 29th Jul 2019, 7:42 pm   #19
Mike. Watterson
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Default Re: (Another) MW/LW interference problem

The modern gear has ceramic disk 1kV X&Y rated caps. I've only seen those fail due to nearby lightning strikes.
The problem is gear with wire links for the chokes and empty holes for the caps.

The LCD PSUs, charger SMPSUs and CFL ballasts (or regular tubes with Electronic ballast) have the problem they use a half or full wave rectifier and electrolytic cap for DC, and then secondary electrolytics if a DC PSU. The electrolytics often have more PSU heat than a valve radio due to zero empty space and dry out. As they dry out the interference rises. Eventually what ever it is may stop working.
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Old 29th Jul 2019, 8:28 pm   #20
The Philpott
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Default Re: (Another) MW/LW interference problem

Post No.17-

Thanks. The real surprise was the effective range of the interference- the test bench is 55' away from the stairlift, with 3 studwork walls and sundry other gubbins between the two.
I just hope none of my neighbours use MW!

Dave
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