AM Radio Noise Suppressor

[Charger Fan]

Two questions I'm looking for help answering,
1. How do you check the radio noise suppressor with a multimeter? Is it a capacitance test?
2. I am replacing the factory AM radio with a factory AM/FM stereo radio in my Charger. I have read you only need a suppressor for AM because FM radios have the suppressor built in. Does anyone know if the factory 1971-1974 Mopar AM/FM stereo's had these suppressor built in and will it cover the AM side of the radio or do I still need to have the external one shown below installed on the coil bracket?

 

[HALIFAXHOPS]

Good question on the radio. Yes they are capacitors so test them like one. Think the MF is stamped into the base. Kind of hard to find also new

 

[HALIFAXHOPS]

Basically a go no go test here not the value.
How To Check a Condenser on a Points Ignition

 

[twecomm]

You did not mention if you have points or electronic ignition ?? On the AM vs. FM and noise question, on a car with points in the distributor, the arcing across the points with the energizing voltage being applied and removed to the coil, by means of opening and closing of the points. This creates a spark that will radiate to an AM radio via wiring associated with the ignition system. Since this spark much replicates the "amplitude modulation", process, or AM radio signals, the radio does not differentiate between the transmitted radio stations signal and "static" created by the points. The capacitor basically helps to suppress the electrical energy created by the sparking of the points, and thus reduces interference to the AM radio. It also helps reduce the intensity of the spark at the points, making the points last longer.
FM, or frequency modulation, uses a totally different method of actual modulation of the transmitted radio signal. By the nature of FM, "frequency modulation", it is not sensitive to interference or static caused by sparking, such as created by the points. In cars such as my 66 Charger, that had points and a factory installed AM radio, there was a similar capacitor on the rear of the instrument cluster to suppress the sparking of the the points style 5 volt regulator for the gauges with those contacts opening and closing constantly.
These caps are not that expensive and chances are, due to the heat they are exposed to under hood coupled with age, I would suggest to just replace it. If I recall correctly, both the AM and AM-FM car radios do have some form of suppression that's internal on the 12 V DC input.

 

[Billccm]

All car radios have a input low pass filter regardless of frequency or band coverage. As explained the condenser is a capacitor I believe around 0.01 uf. These generally never fail in applications where the peak voltage is low (like inside the car interior).

 

[Charger Fan]

You did not mention if you have points or electronic ignition ?? On the AM vs. FM and noise question, on a car with points in the distributor, the arcing across the points with the energizing voltage being applied and removed to the coil, by means of opening and closing of the points. This creates a spark that will radiate to an AM radio via wiring associated with the ignition system. Since this spark much replicates the "amplitude modulation", process, or AM radio signals, the radio does not differentiate between the transmitted radio stations signal and "static" created by the points. The capacitor basically helps to suppress the electrical energy created by the sparking of the points, and thus reduces interference to the AM radio. It also helps reduce the intensity of the spark at the points, making the points last longer.
FM, or frequency modulation, uses a totally different method of actual modulation of the transmitted radio signal. By the nature of FM, "frequency modulation", it is not sensitive to interference or static caused by sparking, such as created by the points. In cars such as my 66 Charger, that had points and a factory installed AM radio, there was a similar capacitor on the rear of the instrument cluster to suppress the sparking of the the points style 5 volt regulator for the gauges with those contacts opening and closing constantly.
These caps are not that expensive and chances are, due to the heat they are exposed to under hood coupled with age, I would suggest to just replace it. If I recall correctly, both the AM and AM-FM car radios do have some form of suppression that's internal on the 12 V DC input.

It's a 1973 Dodge stock electronic ignition.

 

[ffgreg32]

I worked at an electronics store (Team Electronics) during the late 60's and early 70's. I installed hundreds of radios, Fm converters, 8-tracks, cassettes, CB's etc. AM suppression was in 2 types back then. The "ticking" of the spark plugs, and the whistling/whine of the alternator. Suppression was accomplished by using resistor plugs and wires to combat the sparkplug noise, and a condensor/suppressor mounted on the alternator (hotwire bertween battery and alternator) , or inline of the hot wire, as I recall.

 

[twecomm]

The after market 60's and 70's stuff you describe that you were installing, typically suffered from varying amounts of " alternator whine". CB radios ,back when that was a popular thing, were especially susceptible to the alternator whine. You could buy a small inductor, or choke that would typically solve the issues when put in series with the 12 V lead to those and other devices.

 

[ffgreg32]

The after market 60's and 70's stuff you describe that you were installing, typically suffered from varying amounts of " alternator whine". CB radios ,back when that was a popular thing, were especially susceptible to the alternator whine. You could buy a small inductor, or choke that would typically solve the issues when put in series with the 12 V lead to those and other devices.

correct, old school days

 

[Charger Fan]

Good question on the radio. Yes they are capacitors so test them like one. Think the MF is stamped into the base. Kind of hard to find also new

Didn’t have anything stamped on the base or anywhere else. I’d like to get a replacement and should be able to find something with the same micro fared rating if I knew what the rating was. Some on eBay but didn’t really want to spend $50 for it.

 

[HALIFAXHOPS]

Definately not cheap. I have some aftermarked older ones if needed.

Mopar one is sold a while ago

 

[Charger Fan]

I have yet to find the microfared rating in the Service Manual on the factory 2884869 capacitor. Does anyone have that?

 

[Billccm]

It's not a critical value. I use 0.1uf 600V "orange drop" capacitors as my favorite for EMI reduction.