Long Wave interference problem

[MurphyNut]

I listen to my vintage radios down the end of the garden, well away from the house and enjoy very good reception and clear sound. However every now and again I get something to spoil the enjoyment.
Over the past 5 days I’ve been experiencing a lot of background noise on LW almost like the station is out of tune, yet MW is fine.
I have a few battery transistor radios and when they are tuned into radio 4 Long wave I don’t get any problems, I was assuming it’s coming in from the mains supply but as MW is fine perhaps not!
Nothing has changed at the house so I’m a bit perplexed to what’s going on.

One way to 'prove' it is the mains is to quickly unplug the radio, there will be a second or so of sound before it stops working. Unfortunately interference below FM radio in frequency isn't though of as bad these days as long as the majority have TV and mobile 'phone access all is well.

I had a very odd interference problem years ago, every 10 seconds there was a burst of 'hash' all the way from LW to SW on my end of garden loop. Turned out to be a hedge trimmer charger in the "other end of the garden" neighbours keeping said gadget topped up.

[Skywave]

Interference coming in via the mains feed: yes, a real possibility.
Since your battery transistor radios are not affected, when the interference is present, try holding a transistor radio (tuned to LW) close to the mains lead of the affected radio to see if it picks up radiated RF noise. That will establish if the interference actually is mains-borne.
Is only one of your mains-powered radios so affected? Can you run a test with another mains-powered radio? Could the interference be due to a fault in the affected set itself?
If the noise turns out to be mains-borne, then ideally, once - and if - the source is located, you might be able to solve the problem. However such an ideal 'fix' is often not practical. Alternatively, it might be easier to tackle the effect rather than the cause. A coil & capacitor RF filter for the incoming mains supply to the radio might help - with that filter located as close to the radio as possible.

Al.

[MurphyNut]

Thank you very much for this advice, all my sets suffer with this problem. I did as you suggested and held the transistor radio next to the mains lead that feeds my radios and sure enough it started picking up exactly the same interference. So this establishes the interference is mains-borne.
How would I go about creating a filter to hopefully sort out this annoying problem? or perhaps there are mains filters commercially available.

[MrBungle]

I would go round and turn everything in the house off one thing at a time and try and isolate it first. Best to fix that if you own it than the radio if you can.

Failing that, RSGB sell big ferrite rings here: https://www.rsgbshop.org/acatalog/On...ilters_41.html

I wrap the mains lead around them as many times as possible. I’ve only had to do this on one thing so far and that was on the source of a problem ie a cheap wall watt SMPS.

[Skywave]

Yes, ideally, try to find the cause - and then suppress the RF at that source. Failing that, address the effect - a mains input filter. A quick look around the internet reveals that there are many 'ready-to-use' products available. But apart from that, I found the two links below which focus on the problem you have. Reading them gives some insight as to what a typical mains filter looks like, typical performance, design criteria, etc.

http://www.audiomisc.co.uk/mains/filters1.html

http://www.zen22142.zen.co.uk/Circui...ainsfilter.htm

Al.

[Jonster]

If you had a ferrite rod from a scrap set then try wrapping the mains lead around that, a dozen turns should suffice.

[Bobdger]

Have you just installed a network extender?. These plug into a 13A socket, the network cables are feed to one unit from your hub, the other matched unit is connected to your tv or other device. Some of these units radiate a lot of hash on to the mains supply.

Bob.

[Hybrid tellies]

Interference from mains wiring is really bad these days. Sometimes I find that all my mains operated radios are totally useless as even the strongest AM signals on both Long and Medium waves are either being drowned out by a hash or suffer with loud unpleasant background hums and buzzes. Whereas a battery operated transistor radio works really well in the same room.

[MurphyNut]

I've worked around the house switching off everything individually connected to the mains and returning each time to my sets but it's made no difference what-so-ever.
I'm wondering now if this interference is out of my control and coming in from outside.
This is quite a blow to me as up until a week ago I used to spent many happy hours listening to Radio 4 with really good sound on my valve sets.
It's strange as MW is not effected at all, a pity Radio 4 isn't over there!

[michamoo]

"It's strange as MW is not effected at all, a pity Radio 4 isn't over there! "


But it is from Crystal palace on 720Khz which is sort of near to you.

[music-centre]

One of your neighbours has probably bought some gadget giving out loads of interference or they have something that's recently become faulty and now gives out noise.
After I moved house a few years ago, my mains radios were unusable on LW and MW was nearly as bad even with everything in my place switched off.

It was like that for probably 9 Months and then suddenly one day it was gone.!
Pretty quiet now but I guess something similar will be back!
Steve.

[PaulR]

I greatly improved this by putting a class x cap across the pins inside a couple of 13A plugs. You can move them around to get the best effect. Just be aware that the caps carry a small charge when unplugged and can give a bit of a "nip" if you touch the pins. It isn't anything serious and you can easily short them to discharge the cap.

[MrBungle]

If you’re going to do this stick a 1M resistor of suitable voltage across the X2 cap. I’ve had the nip and don’t wish to recreate it

[MurphyNut]

Originally Posted by PaulR

I greatly improved this by putting a class x cap across the pins inside a couple of 13A plugs. You can move them around to get the best effect. Just be aware that the caps carry a small charge when unplugged and can give a bit of a "nip" if you touch the pins. It isn't anything serious and you can easily short them to discharge the cap.

Thanks Paul, I'll give this a try, what microfarad value should I consider.

[PaulR]

Sorry for the delay Clive. I used 0.1uf

[Hybrid tellies]

Did you use just one cap across live and neutral or did you also put one across the live and neutral pins?

[Herald1360]

What's the difference?

[PaulR]

Yes across live and neutral. I found that the cap would just fit into the space where the cord grip should be.

[ukcol]

Hi Clive

I sympathise, I had a problem with R4 LW interference although not quite the same situation as yours.

See

https://www.vintage-radio.net/forum/...ad.php?t=99980

If you look at post number 21 in that thread you will see details of a tuned frame aerial I made in an attempt to solve the problem. Later in post 24 Chris, (Herald 1360) pointed out that I could have achieved the same results with a ferrite rod which is probably the easier route to take.

One aspect of interference worth mentioning is that engineers often speak of "mains borne" OR "air borne" interference. In practice it can often be both. You can have an efficient filter in the mains supply to your receiver only to be defeated by air borne interference re-radiated by the mains wiring in the building.

Something else worth mentioning that may or may not be relevant to your problem is the earth path. As well as having a clean mains supply and a good strong signal from your aerial, a clean earth path is desirable. The earth path in a domestic mains supply is a safety earth that may be quite dirty (contain noise). A separate clean earth (perhaps water pipes that don't have plastic in the path) may improve matters.

As others have said, identifying and killing the source is the best solution but often nowadays very difficult.