Radio problems
 

Hi, for the past 4-5 years I've been having trouble with the factory radio, i really like it because it simple to use and you don't need a magnifying glass to find out how to change the station. But on lower frequency channels , ex. 540, 600, 620, 830, and up to about 910 it just makes a chk, chk, chk noise very fast. But it doesn't do this on higher channels, (like 1210) or on FM, just lower channels on AM, i'm finally getting angry at it, because you cant listen to those channels, as i live in a rural area with few stations, they are all in that range except a few. Now I'm finally going to trouble shoot now. Any one else have this problem ever. I know this must be hard to understand, but the noise is a chk noise, you can still hear the station but this is "over top" of that. Sorry for the confusing way i describe this but i don't know how else to explain it. This is for my 2000 XLT power stroke in my sig. The radio is the premium for that package, it was extra money, it has the 6 programmable buttons at the bottom.

I have the same problem...(2000 7.3L 4x4), except not quite as bad as yours. A couple of quick questions. Does the interference "chk" change speed with enginer RPM? Mine doesn't. Also, is it there without the engine running, but with the key in the 'run' positions? I only have the noise when the radio station signal strength is weak.

Mine isn't to the objectionable point yet, so I haven't traced it down yet. In my case, I suspect the fuel pressure pump starting and stopping.

BTW, I'm a 55 year Ham radio operator and a Professional Engineer.

I don't have time to research the problem for about the next week - my wife & I are leaving for our summer snowbird trip (out of the desert heat). As soon as we get there, I'll see if I can trace my noise down. This is when I do mosts of the mods to my truck. PM me so that I can have your return address.

Bob

I can't help much, but what I can say is I get a bunch of weird "static" in my aftermarket head unit. If you have some gauges or a CB or other accessories wired in the truck, try to move those wires away from the antenna cable and see if it helps.

RPM's don't affect it, it is not there when the ignition is turned to "radio" but in the run position it is there. It was there before i started wiring fog lights, and CB's in the cab.

bringing this back to see if anyone else has had this problem.

So the noise was there before you added any aftermarket electrical items?

yes it was there before anything else was installed..it gets even worse if you plug anything into the 12v socket (cell phone charger) Then a squeeling noise completely covers up the radio so you can't even here it anymore.
If you turn the key backwards it is gone.

Is it possible that there's an issue with the power supply to the radio? You could try isolating the main power feed to the radio and running a wire directly to the battery. That should tell you if the noise is caused by the power supply or if it's coming from the antenna.

ok, thanks i'll try that tommorow.
thanks again

If the interference is there with the key in run, but not in accessory, something is definitely causing interference. Put the key in run, and pull fuses for different items. Maybe you'll get lucky and find a circuit that is causing it and can work from there.

If I had to start some place, I'd be looking at the digital communication bus that ships information around between on-board computers. It's square-wave information, and square waves are the sum of a sine wave and an infinite number of odd harmonics. Remember, Bob?

I suspect you're hearing some of those harmonics at the "word rate".

Data cables are ideally twisted, shielded pair, and there's nothing in the wiring diagrams to indicate that they are. I haven't torn into any of my harnesses to see for myself, however.

Although less-suspect, another source of square waves that is not engine speed dependent is the pulse-width-modulated panel lights dimmer circuit. Remember, that circuit feeds directly into the radio. However, it should be easy to determine if it's the source. Any noise with the lights off?

Pop

How about just going around all that and running a dedicated power and ground wire to the radio?
Straight from the battery.

I suspect that if this were a power purity problem, the noise should also be heard at least in the upper-end AM frequencies, too. So, if it's receiving radiated noise, the additional wiring will all be for naught and a waste of time, and the noise will still be there.

If I wanted to ensure pure power (assuming I suspected it to be a problem), a large electrolytic filter capacitor across the power input (and ground) would be easier to accomplish than running the wires out to the engine compartment.

I have noticed this noise, too, but not to the extent that it's really annoying. As I recall, it's more pronounced at only certain frequencies. That lends more credibility to the hypothesis that the data bus is the source.

Pop