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Streetlight interference?

Posted: 18 Apr 2016 09:17
by daveB
For the last few weeks I've been getting interference on the lower part of the FM Band in the evenings. It spreads well below 80 MHz and manifests itself as a long series of humps about 200 kHz apart - 10-15dB above the normal noise floor. This is more than sufficient to mask weak signals. I recorded the spectrum overnight - and lo and behold it switched off abruptly at 05:42 - a few minutes before sunrise. On 89.4 - which was just noise Fr Musique abruptly appeared at the point it stopped.

So the next step is to set up the recording from about 7 pm tonight and then go and watch when the street light turns on - it should be about about 20:20 as sunset is 19:59. If it does appear when the light comes on I'll be out there with the portable to confirm it - the street lamp is only some 10 feet away from the rotatable aerial.

There was meteor activity last night - which I'm pretty sure would have yielded RDS if the interference wasn't there.

Has anyone come across this sort of interference? If I can confirm it is the street light - how long would it take to get the council to sort it out?
FM Interference.jpg

Re: Streetlight interference?

Posted: 18 Apr 2016 10:45
by Andrew Webster,Wigan
Ah yes the good old streetlamp stood there looking innocent but it isn't lots of people have had freeview knocked out by a faulty streetlamp even if it's lit ok.
Councils know of this problem so contact them as to how long it will take well our's take a few days but it could be longer.


Andy

Re: Streetlight interference?

Posted: 18 Apr 2016 11:23
by daveB
Thanks,
I'll make sure to blame the streetlight for the odd pixellation on Freeview! They can't argue with that. Interestingly it is the only 'fishbowl' style streetlight left - the others have been replaced with the ones that only shine the light down. I could complain it shines in the bedroom window - but we have thick curtains.

Re: Streetlight interference?

Posted: 18 Apr 2016 11:34
by John Faulkner, Skegness
If it affects local reception then I guess the council will be more likely to act.

I used to have street light interference at my parent's house many (many!) years ago. It was always a transformer problem. The council always fixed it promptly when I reported it. Things may be different now of course.

There's a street light directly outside the shack window and, so far, it hasn't been a problem.

Re: Streetlight interference?

Posted: 18 Apr 2016 14:30
by satnipper
Normally a faulty insulator or transformer. Mention of fire risk, health and safety, bits falling on people's heads should get a council bureaucrat's attention.

Re: Streetlight interference?

Posted: 18 Apr 2016 20:51
by daveB
OK - it does not appear to be "the" street light or the other one 50 yds away. The interference abruptly switched on at 20:03. but "the" street light didn't come on until 20:12. The other one had come on a few minutes earlier. Standing close by the nearest streetlight I got Fr Musique on 89.4 at around 4dbf on the Tecsun - as I walked toward the next street light the dbf went up to over 20dbf of noise and then faded back down and at the next street light I got Fr Musique at 6dbf.

A bit of further investigation strongly suggests that a pair of ornamental solar lights a couple of gardens away from our house are responsible - they are right at the bottom of their garden by the fence and just the other side the Tecsun is showing 30 dbf.

So next question is - how can I diplomatically approach the neighbour - so as to investigate it further?

Re: Streetlight interference?

Posted: 19 Apr 2016 18:14
by Andrew Webster,Wigan
Hmm that's a difficult one and solar lamps would be the last thing I would think of causing interference I wonder what type of lamps they are.
I can only think the LED driver chip responsible but not heard of those lamps causing it.

Anyway hope you can sort it.

Andy

Re: Streetlight interference?

Posted: 19 Apr 2016 23:45
by daveB
I wouldn't have thought the solar lamps would have driver chips myself and more investigation is needed - like timing when the various lights actually turn on. The interference came on a few minutes later today - but for an hour prior to that some background interference had appeared!

Re: Streetlight interference?

Posted: 20 Apr 2016 00:01
by Julian Hardstone
I have pulled these things apart in the past and they have only the most rudimentary single-transistor oscillator to generate the 3.3V needed for the white LEDs. They seem usually to run at below 100kHz, but that would give 'odd' harmonics every 200kHz or so. I'd be rather surprised if the harmonics would be sufficiently strong to radiate qrn at VHF, so I will be interested in any further investigations you can make

Good luck - Julian

Re: Streetlight interference?

Posted: 16 Mar 2017 22:44
by daveB
It's back again!!!!! The sun is now high enough, and we have had some nice weather, to illuminate the back garden of whoever has the offending item(s). Looks like I will miss out on evening tropo lifts unless they are strong enough. :(

Re: Streetlight interference?

Posted: 02 Apr 2017 18:04
by KPC850
Julian Hardstone wrote:
20 Apr 2016 00:01
I have pulled these things apart in the past and they have only the most rudimentary single-transistor oscillator to generate the 3.3V needed for the white LEDs. They seem usually to run at below 100kHz, but that would give 'odd' harmonics every 200kHz or so. I'd be rather surprised if the harmonics would be sufficiently strong to radiate qrn at VHF, so I will be interested in any further investigations you can make

Good luck - Julian
I opened up some of these Solar charged garden LED lights too.

THe first one as well as a single AAA NiMH battery it had just a 4-pin IC with name 'HW012' and a 100uH inductor that looks like a resistor on the little circuit board

with the light running (dark, LED on) it was switching at approx 150kHz. Holding a portable radio right next to it, harmonics of this could be received across the MW band, but moving radio away some inches the harmonics rapidly diminished in strength.
The switching frequency drifted down in frequency as battery voltage dipped and LED got dim

(2 other - non-functioning ones - different make - I broke up had a similar 4 pin IC but with ICs named 1205 in one, and DC1205 in the other and both with a 'resistor-like' 120uH inductor)

the fact that the wiring in these solar charged lights is so short (and not connected to any external wiring), it is not going to be able radiate interference any distance to be concerned about.

No interference noted on FM band with the functioning light even right next to telescopic aerial on radio.

Re: Streetlight interference?

Posted: 02 Apr 2017 20:38
by Andrew Webster,Wigan
We have a mains powered dusk to dawn light at the back of our house just below my band 1 aerial and that radiates slight hash on band 1 when it switches the waterfall changes colour it's only slight doesn't stop me seeing whats happening in any way but no problems on FM.

Andy

Re: Streetlight interference?

Posted: 15 Jun 2017 21:59
by daveB
Update:
Lovely sunny weather so all the solar lights will be running. Last night (14th) the interference was conspicuous by it's absence. Today I spotted the council had sneaked in and changed the local street lights to LEDs - then I noticed that the solar lights on the side of a near neighbour's garage are dead or gone - he's nice twinkly lights in a bush - so I still don't know the cause. Hope the cure is premanent.
I will say one thing though. I should be able to see a lot more stars on a clear night as the illuminations is all downwards.