Testing the Radio Noise Suppressor?

Cougar Community Classic Cougar Maintenance Restoration and Repair
1

Hey Gang,

So the other day I was cruising the Eliminator and listening to some good ol’ AM stations, and I noticed that when I came to a stop with my turn signal on I am getting a “crackle” feedback into the audio system.

I thought the radio noise suppressor was supposed to take care of this, but maybe mine has finally given up the ghost.

So I’m wondering, is there a way to test the radio noise suppressor? Does anyone have any insight on voltmeter measurements to expect for a good vs bad noise suppressor?

Thanks!

2

I think to test one you would need to own a Fluke meter or equivalent with a Capacitance function. I would expect a reading around 200 MF if it is functional. An open reading would mean it is shot.

3

Thanks Royce! Now I’ll have to check my Fluke and see if it will do the trick (not a normal measurement for me, but I do have a pretty robust model).

4

I have a NOS one so it is a curious thing to me to read what it should be versus an old one that has been installed for decades.

5

So my meters are all pretty basic, I don’t have any that measure capacitance. As such I set the meter to RX1 and measured resistance. I did not expect to see what happened.

The NOS unit shows resistance briefly then it shows open. If I reversed the polarity of the leads, it shows the exact same thing. I believe the Capacitor is charging then shows open when it is fully charged. Any electronics experts are free to comment here. I am not sure my conclusions or methods have any relevance.

I did find a General Motors radio static suppressor for sale on eBay with a rating of .5 MF.

6

Caps don’t pass DC. What you saw was the meters integration time, some function of 60hz depending on the meter. You can get a relatively inexpensive multi meter that will measure capacitance. What is expensive is being able to test really big capacitors. Basically the meter charges the cap and then measures how long it takes to discharge into a given resistance.

7

I measured a used radio noise suppressor (capacitor) @ .458 uF (not 200 uF).
A similar physically-sized points capacitor measured .232 uF. YMMV

Another simple test for a capacitor would be to measure the resistance across it on the highest scale of your ohmmeter - it should read full-scale (infinite resistance). Any less indicates a leaky (failing) capacitor.

Another test would be to measure the capacitor breakdown voltage but that is probably beyond the scope of this forum.

Note that some Fords used chokes (inductors) for IVR noise suppression. I’ve never seen one installed on a Cougar but these parts come in a dealer-installed radio kit.

8

Do you have the factory radio?
Do you have the OEM sequential system?

1 Like
9

Yes, all original factory radio (AM/8-Track).

I converted the sequential system to the full solid state setup that WCCC sells for the '70 a few years ago. Didn’t have an issue with radio crackle until recently.

Measured my suppressor’s capacitance yesterday: 0.475 uF
So very close to what Bill measured on his used one.

10

Are you using LEDs or incandescent bulbs?
Is the cackling synchronized with the turn signal flash cycles?

Vic Yarberry
Cougars Unlimited LLC

11

Hi Vic,

Yes, converted all to LED (except headlights), and yes the crackling is synchronized with the turn signal flash cycles.

12

Does the cackling noise occur across the AM band or just on some channels?
Vic Yarberry
Cougars Unlimited LLC

13

Not sure on that. I’ll have to test it out next time I have the car out.
I can say that it doesn’t seem to occur when I’m using the 8-Track player, if that matters.