Ignition Noise Picked Up by Radio

This suggests that the interference is coming into the radio via the antenna connection, since with FM interference is better rejected than AM. If the interference were coming in though the +12 power supply connection, it is likely that the interference would be the same regardless of the modulation system (band).

I'd check to make certain that the radio ground had a short, hard connection to a point on the chassis of the car as close as physically possible to the radio. A long ground wire is an antenna.

Go to a car stereo shop and let them analyze the noise and recommed whatever filter device they feel will cure the problem. They see this stuff all the time, especially with the high power boom boom stuff.

-ANT

ANT's not wrong. Me, what I'd do, is disconnect the antenna and insert a

50-ohm dummy antenna plug in the radio. If it goes real quiet, you'd know the noise was coming in through the antenna feed. If not, then power supply needs filtering or bypassing, or a quieter ground needs to be be found. Do as ANT sez and get help from the boom-de-boom-de-boom kids with their hats all on backwards and stuff.

You NEED some resistance in the ignition secondary circuit to damp out the RF oscillations which show up as audio noise on your radio. Since the very early 60s all VW have come equipped with spark plug connectors which contained resistors and distributor rotors which also contained resistors. If you are still using the OE style of parts here you will find that your ignition is well suppressed. There is no advantage to using resistor plugs, too.

If you have replaced your spark plug wires with a set which does not have resistors in the spark plug connectors, then switching to resistor plugs would be a benefit.

In the long run it is cheaper to ue the OE setup (resistor rotor, resistor SP connectors, plain spark plugs) because the resistor SP connectors will outlast many spark plugs and you pay a lot more than the paragraph above suggests for spark plugs with resistors. OTOH, the resistors in the OE style SP connectors occasionally fail and cause problems until you figure that out and replace them, so there is some advantage to just getting a new resistor with every new plug.

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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That's funny that you said that..............for years I've been threatening to drive thru the hood with a loud system blaring opera just to see the looks on all their faces.

Of course I'd need an armored personnel carrier to do this in. Bwhahaha

-ANT

In the bad old days of 6 volt cars one trick was to run solid wire spark plug wires along with resistor plugs. This gave you some RFI protection while allowing the full voltage to reach the plugs (the resistance was at the end of the circuit)

Not sure if this is a correct theory or even explanation, but it seemed to work for the most part.

-ANT

I did that when I was cruising the Main Drag in Dallas for a year or two,................I at least played something that most could recognize , whether they knew who it was or not. It was a tape of Beethoven's 5th...............and I sometimes took home audio speakers and hooked them up for better volume.......and put them in the bed of my toyota pickup, firing up of course. No armored vehicle needed.

Remove "YOURPANTIES" to reply MUADIB®

It's is not, it isn't ain't, and it's it's, not its, if you mean it is. If you don't, it's its. Then too, it's hers. It isn't her's. It isn't our's either. It's ours, and likewise yours and theirs. -- Oxford University Press, Edpress News

threatening

If you don't, it's its.

and likewise yours

Does this not suggest that it is not the antenna? The external aerial is FM is I am not mistaken, so the interference is from another source. It might contain frequencies that affect FM more than AM, but I suspect power or ground.

Would a short ground lead not act as an antenna of a different frequency? Replace the cable with shielded cord?

Or perhaps there is something else emitting interference - fans? that sort of thing?

HTH Anto

Or it could be a bust unit! just a thought...

Bad old days? 6 volts was enough to get me to work today.. ;)

Charlie Houston, TX '66 Bug "Whitey"

Early suppression wiresets used a sort of carbon-loaded string as the center conductor. These wires were fragile and also had a lot of resistance. They were replaced in the mid 60s by copper wire and lumped resistances in the SP connectors. These wiresets are quite reliable.

You certainly have the right idea.

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Wagner. Ride of the Valkyries.

The very nature of AM makes it more susceptible to interference. That was one of the key selling points of the frequency modulation system when it was introduced in the 50's. The same sparks and whines that totally overwhelm AM signals can be successfully rejected by FM demodulation. If you hear a lot of interference when listening to AM and not much when listening to FM, it suggests that you are hearing the interference on the antenna feed. BUT it could also be creeping into the radio chassis through the power supply and radiating all over the inside of the thing there. Take it to a pro.

As it is shortened, it becomes sensitive to (or does a poorer job of earthing) higher and higher frequencies, and less so at lower frequencies. Get it short enough and it only acts as an antenna (or does a poor job of bypassing) frequencies so high that your AM/FM radio does not care - it ain't listening out there.

Sure -- anything could be causing it. If the noise happens only when the fan is on, well, there you have it.

The external antenna serves both as the AM and FM antenna. There is even a special trimmer in most radios to null out the capacitance in the antenna for the AM input.

VW even sold a special type of grounding clips for the front wheel bearings in the early 60s. I heard about them and bought a pair. One fit under each grease cap on the end of each front axle. They seemed cool, but I could never tell that they made any difference.

They were supposed to ground out static charge generated by the rubber tires. It always seemed to me that the bearings themselves did a good enough job of this.

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Ok having done a little research now I agree, and it shows the gaps in my knowledge...I also found this -

Could it be am amplified aerial that isn't receiving power?

Anto.

An active (powered) antenna?!? Kewl. The link presents a troubleshooting procedure.