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bear;
The Bendix AM radio in those cars is one of the best radios ever! Unfortunately, with excellent receiver sensitivity comes sensitivity to noise...all is not lost however...
Radio noise is caused by two distinctly different mechanisms. These determine the path by which the noise finds itself into your radio, and the manner in which they should be reduced/eliminated. You must first determine the nature of the noise:
1. Generator noise, caused by the sparks which inevitably occur at the generator brushes, and CONDUCTED along the power system of the vehicle...verified to come in on the powerline of radio if the whine remains (at typical volume control settings) with engine running after antenna is disconnected...options to reduce: (ignition type) capacitor at Genny output D+ terminal to D- (housing), add in-line power filter to radio power lead, relocate where power for radio is taken (from ignition switch to directly from battery or fuseblock), or combination of the above...
2. Ignition noise from spark plugs, caused by radio frequency (RF) component of the ignition pulses, and RADIATED from the ignition wires...verified to come in on the antenna wire if you temporarily power the radio from a spare battery, while motor is running...options to reduce: Verify good, clean connections at all ignition wires ends, also 1kOhm resistor ends which clip onto sparkplugs, located at the ends of the plug wires, are in place, and have not been removed, verify good ground on antenna coax braid-to-fender at base of antenna, and at radio, add ground strap (braid) to hood and exhaust system,
Its best to try the suggestions one at a time in order to get a good with/without comparison of any improvement each one might make (or not)...noise locating and abatement is tricky that way...
Cheers. That should keep you busy for a while...
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