Radio interference

testrider

testrider

Active Member
In the quest iron out little niggles to make HOT more enjoyable to drive my attentioned has turned to the radio. It's a period Motorola with an aerial on the roof and a single speaker, but it only picks up Radio4. With the engine at idle the sound is clear, but above 1500rpm the radio picks up a crackling sound. There's no white noise when tuning for another station either.

Suppressors I hear you say! Well, there are little blue capacitor like things dotted around the engine bay, on the coil, dynamo, regulator etc, so I think I'm covered for them, but could they all be broken or is the radio just not very good?
 
Paul

I had a similar problem with Lady C. She has no aerial fitted but does have a radio for my ipod.

RF noise is generated from a number of areas in a car. If it increases with engine speed then it is more than likely the dynamo. Suppressors are just capacitors like the condensor in the distributor. The dielectric in a capacitor (the insulation between the metal plates) breaks down after a while rendering it useless. I'd replace all the suppressors that are fitted.

As a last resort, and I discovered this purely by chance, fit some modern spark plugs as NOS ones are less likely to have effective suppression. This cured all my radio crackles on Lady C.

Dave
 
If it's a crackling noise, then it's most likely ignition. The dynamo tends to sound more like a high-pitched scream. There should be about 10-20 k ohms resistance in the plug leads. If resistive ones have been replaced by by plain copper, then resistive plug caps are needed or else a cut lead suppressor in the distributor king lead. Other than that, make sure there is a good earth to the radio case.
 
Thanks for the suggestions. It has old NGK leads and new NGK plugs fitted, but I don't know what their resistance is. If it was the plug leads, why would it only become apparent with the revs above 1500(ish) rpm, wouldn't it make a noise at all revs?
 
testrider said:
If it was the plug leads, why would it only become apparent with the revs above 1500(ish) rpm, wouldn't it make a noise at all revs?
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If it was HT interference it would sound like sharp clicks at idle, at a rate of around 2Hz (ie 2 per second), with the clicks becoming more frequent as you rev the engine. Suffolkpete is correct in that generator interference sounds more like a scream that increases in pitch as you rev the engine. This is because generator interference is at high frequency due to the quickly changing magnetic fields in the dynamo coils as they rotate. With HT interference the clicks don't appear to change pitch because they're low frequency. They do become more frequent (which in turn affects their pitch) but your ear won't be able to distinguish that at such low frequencies. There will just be more clicks per second.

There's a huge amount of infomation available that explains RF interference on ICE and how to counter it, but it often comes down to trial and error.

Dave
 
Thanks Dave, when I get bored of rear springs and oil leaks I'll take the radio out and check the wiring.
 
stina said:
DaveHerns said:
Is there anything worth listening to on medium and long wave?
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Absolute Radio , Classic gold . There are a few down here .
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You can't beat the nostalgic experience of sitting in that light airy cabin, with the thin-rimmed plastic steering wheel in your hands, with Classic Gold on the AM-only Motorola as you cruise down the quiet country roads :D
 
With the engine off, how well does the radio work? If it is not very sensitive and cannot pick up any stations other than Radio 4 on LW, then, any interference issues aside, you could simply have a problem with things like:-

1. outer co-axial screen on co-ax between radio and ariel not being earthed to chassis properly.

2. as already mentioned, the radio case isn't earthed properly.

3. poor continuity in inner co-ax conductor between ariel and radio.

4. insulation breakdown on co-ax.

You can check all of the above with a multimeter on resistance/ohms setting. Even easier, perhaps, is to remove the radio from the car and connect it to a 12V supply with a bit of long wire stuck in the ariel socket. If it works OK on the bench, problem must be with earthing or co-ax connection to ariel. Alternatively, if you have another old radio lying around, you could connect this up in the car to see if the reception/interference problems improve.
 
Sorry but I think AM radio is a waste of time these days .Just think of the stations you could have got when the cars were new , Radio Caroline , Radio London and other pirate stations , Luxembourg to name but a few
Absolute Radio , Classic gold
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- that's why I said worth listening to !
 
It's not too bad around Glasgow. We have a local station, Clyde2, broadcasting on 1152KHz. They mostly play 60s and 70s music. I sometimes like to tune in for that authentic 70s sound you can only get from AM lo-fi :) .
IIRC, many of the singles recorded back then were produced so that they sounded "punchy" on the AM car radios and domestic "trannies" of the day.

TBH, it is also very nice to have the quality and choice of FM & digital as well :) .
 
I agree that there isn't much to listen to on MW now, but that's not the point, I'm trying to figure out why it won't pick up anything other than Radio4. If I can make the standard radio work without any crackling then I can think about changing it for an FM radio or adding a lead for my ipod.

With the engine off it still only picks up Radio4 so I'll start with JVY's suggestions of looking at the ariel wire and casing.
 
Has this radio got a trimming screw ? If so I think you tune the radio to a station about 200/250 on MW and tweak the screw till the signal is loudest
I tried my daily driver on AM today and there aren't many stations
 
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