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MG Midget and Sprite Technical - Radio Interference

Looking for any advice on dealing with radio interference - and do NOT start off on how much nicer it is to just listen to the exhaust note!

I am getting a swooshing noise on the radio. Nothing when I first start the engine and set off, but it gradually increases over the first few miles. Noise is a bit like the sound of waves drawing back down on a shingle beach. No crackle as one might get from ignition or buzzing like from a wiper motor, just this swooshing noise.

I added an extra earth wire to the radio chassis but that has made no difference. The thing that is puzzling is that it isn't speed related but the noise increases in volume the longer I drive.
Guy Weller

Sounds like its related to a component warming up somewhere as the operation of the car or radio increases with time to me. Used to get it on old transistor based radios as they got older and the insulation in a component leaked out and the component begin to fail. Radio would be fine to begin with.

Have you changed anything with the car or radio or aerial?
Dave Squire (1500)

something warming up would be my guess as well - perhaps something or harmonics of something in the rectifier circuits in the back of the alternator.

The P6 does a high pitched whine on it's radio that's definitely engine speed related.

Or it's something wrong with the actual radio. Is it on the whole frequency range?
Rob Armstrong

Thanks for replies.
The story is this: I used to have a Sony radio which was quite good - certainly good enough for my ears and for the mobile listening environment! It was fed through a basic wing mounted aerial.
Eventually the Sony packed up - too much damp and water around I think. After doing without - and listening to the induction and exhaust notes - last September I lashed out on a £49 Halfords "special" a Pioneer I think it is. Main selling point being that it has bluetooth (for my phone) and a USB port on the front.

Connected it up and all worked well. Then one day some low life had a go at my Sprite (a first in 20+ years). Nothing serious, they snapped off the aerial and pinched my valve caps. (rough neighbourhood). I replaced the aerial with another cheapie from Halfords.

I am not sure that any of this relates to the radio problems as I cannot really recall when it started, but I don't think it was as a direct consequence to the aerial change. It just sort of crept up on me.
Guy Weller

That swooshing noise is similar to what we used to get when we drove along the M6 at night at 70 -(just)- in the late 60s and early 70s at night. There would be a sort of whistle noise going up and down the frequencies and underneath that a sort of whooshy sea wave / swell noise. The volume would change as well and of course someone needed to keep retuning it as we went along. We were listening to Luxemberg and Caroline. (I assume that the BBC wouldn't pay overtime at the time). The M6 was empty (no crash barriers or lights either).
The problem we had was that I lived in a rough area and the bird (now SWMBO) lived 14 miles away in a nice place. So portable tranny radio with big batteries had to go out of the Victor or Moggie when I parked outside the house. (I lived in the lock capital of the empire so no trouble for anyone taking stuff from cars). Therefore no aerial (would have only been vandalised anyway) so poor reception during the wrong parts of the wavelength as we went along the road. It was fine in the day time with BBC reception.
That radio lasted years and was still going when we chucked it for being too big and bulky and having no cassette player. (Before we chucked the cars, I had my 1970 Moggie from 1971 to mid 1979 and hammered it).
I'd check the aerial for connectivity first.
Dave Squire (1500)

So are you saying I should check that the aerial is plugged into the back of the set properly?
Guy Weller

Is this just a radio or does it take a CD? if not can you use it as an amp in some way? If so use the CD function / other input to check if the unit is OK.
If not above then I would check the aerial itself, the aerial connectors and the input to the unit to ensure there is no damage. Cheaper electrical units tend to have flimsy connectors that are easily damaged. (not a critiscism by the way, I am not putting an expensive bit of kit in my car) If that all seems OK put the radio unit in another car or the other way around and see what happens when its in there.
Fault find to the problem part. Is it the aerial, the radio or the car? Then fix it.

I know I am talking to the converted so ... Wheres my hard hat?
Dave Squire (1500)

Dave, Thanks. That's just the sort of basic help I am after! I can logically fault find mechanical problems, but for some reason when it involves invisible radio waves that to me create mysterious effects my normal logic approach goes out the window!

I will give it a try with the CD and also try playing some toons from my phone through the USB port. Only thing is that the problem isn't instant - it takes a while for the noise to pick up so this will involve a few trips out in the Sprite, just to test it. Oh dear!
Guy Weller

Yes sounds like a real chore. If you want me to test it (you said it was a mark 1 sprite didn't you?) cos you can't be bothered just let me know and I'l arrange to fly up, I'l even put the petrol in! Sounds like on a good day this would be a great excuse for me to have a drive. supposed to be working all day today ... hmmm.

BTW How bad is the snow your way? Since coming over here in 78 its never been as bad as in the West Mids and certainly not as bad as the North and Wales. We always feel like the bad weather news is virtual. (virtually not there at all). Although we do care.

PS I would unplug the aerial when testing with CD so no other effects at all. The only other thing is the speakers but chances of problems coming on slowly from them are very remote. They tend to be s or b. Remember if you need to test, metal coat hangers make good arials as well with good contact :-) (My Itals all had such and were fine for reception).
Dave Squire (1500)

Dave, This is on the MK1V Sprite. The MK 1 is still just a bare shell with welding still to be done, its a long slow job that one!
No snow here in Cumbria, well, not in this part of Cumbria anyway. But it is surprising what a distance of just a few miles makes!
Guy Weller

Glad to hear the weather is OK. Thats how it is here. All hell can break loose around us but usually we have a calm and relatively mild bit compared to even just 5 miles away.

Good luck.

Now out to do those bits that need doing from the long run on Thursday. Three layers, hat, woolly socks.
(I am becoming a wimp!)
Dave Squire (1500)

This thread was discussed on 24/03/2013

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