PCM generated radio noise on 146.520

[TvSteve]

I know this is a known problem but someone told me he saw a fix, filter, posted on the net. I searched high and low and had no hits. I'm taking the 99 SW2 on a road trip, NY to Colorado next month and having it would be useful. Any known workaround?

[holydiver]

I wish I knew...I have the same problem.

[adventureoflink]

what exactly is this problem? is it bad? first I've heard of it to be honest...

and if this is a radio frequency I'm guessing I need an advanced radio or a police scanner to pick it up eh?

[TvSteve]

Originally Posted by adventureoflink

what exactly is this problem? is it bad? first I've heard of it to be honest...

and if this is a radio frequency I'm guessing I need an advanced radio or a police scanner to pick it up eh?

You would need a 2 meter ham radio for this to be meaningful. The PCM is generating a rf signal that is picked up at 146.52 which just happens to be the ham 2 meter national call frequency. This has been a problem from day-1 of Saturn. I just brought it up after I was told of a possible cure.

[adventureoflink]

Originally Posted by TvSteve

You would need a 2 meter ham radio for this to be meaningful. The PCM is generating a rf signal that is picked up at 146.52 which just happens to be the ham 2 meter national call frequency. This has been a problem from day-1 of Saturn. I just brought it up after I was told of a possible cure.

Interesting... does anyone know what exactly is broadcasted?

[OldNuc]

Probably the processor clock frequency. High Q series resonant circuit tuned to 146.52 across the battery positive - negative for starters.

[adventureoflink]

Originally Posted by OldNuc

Probably the processor clock frequency. High Q series resonant circuit tuned to 146.52 across the battery positive - negative for starters.

Gotcha. was gonna say it'd be interesting if it were like a subliminal message for those who have advanced radios (the HAM TvSteve speaks of, or a police scanner, etc) and somehow tuned into that frequency, it would loop "buy a saturn... buy a saturn.. a different kind of car from a different kind of company..." over and over and make you buy a Saturn.

[OldNuc]

Seems to be much comment on the intertubes but a complete lack of coherent solutions. Not even any viable suggestions. Seems to be a problem on 146.79 as well which s also most likely the PCM clock in the vehicle involved.

[TvSteve]

Originally Posted by OldNuc

Seems to be much comment on the intertubes but a complete lack of coherent solutions. Not even any viable suggestions. Seems to be a problem on 146.79 as well which s also most likely the PCM clock in the vehicle involved.

Your right on both points. Signal is radiated off the pcm data lines, clearly created by a cpu clock.

[OldNuc]

Hi Q series resonant filter across battery to kill it. Batteries make real good filters but they are no good at the higher RF frequencies. The PCM cable in the car may be carefully wrapped with aluminum foil which should be grounded with a good ground strap, not wire.

[kg6mvb]

Ouch...bad clock choice.

Along with the other suggestions, here are a few more.

An HT with the antenna removed makes a good signal sniffer. If you have too much signal, try the third harmonic (439.56).

If you can pinpoint a source, try putting a snap on ferrite core(s) over the lines as close to the source as possible. Shielding the lines can't hurt either. Finally experiment with antenna locations. You may not be able to get rid of it, but maybe you can lower the level a bit.

Good luck and 73

[OldNuc]

The Gen-2 PCM is inside the car and the entire wire bundle runs through the firewall close to the interior wire harness.

[TvSteve]

Originally Posted by kg6mvb

Ouch...bad clock choice.

Along with the other suggestions, here are a few more.

An HT with the antenna removed makes a good signal sniffer. If you have too much signal, try the third harmonic (439.56).

If you can pinpoint a source, try putting a snap on ferrite core(s) over the lines as close to the source as possible. Shielding the lines can't hurt either. Finally experiment with antenna locations. You may not be able to get rid of it, but maybe you can lower the level a bit.

Good luck and 73

Here's what I found. Holding an HT, no antenna, up to the OBD port S9+60, next to the battery leads 0. Have 2 snapon ferrites on all 4 of the pcm harnesses and reduced signal 2 s-units, still not usable. Signal is radiated from the data/clock lines and what makes it worse is I'm using a scanguage and a ultraguage, all plastic and excellent antennas. This is on a SW2 and antenna is on rear of roof fed with double shielded coax. Just a note, there was a posting on one of the ham boards how a fellows wife's S car would stop his scanner turning into the driveway.

[OldNuc]

The digital data is at the data port and your scangauge and ultragauge are not helping at all. I would disconnect them and see if there is any change at all. There is only a single data line in the ALDL port unless the SDM has the same clock.

[TvSteve]

Originally Posted by OldNuc

The digital data is at the data port and your scangauge and ultragauge are not helping at all. I would disconnect them and see if there is any change at all. There is only a single data line in the ALDL port unless the SDM has the same clock.

Disconnecting makes a slight change but not worth the loss of information. If I didn't have the gauges I would just cut the data lines at the PCM and replace with shielded cable.

[OldNuc]

That may or may not fix it.