It's kind of a pain to swap out my power supply, but I'm going to see if I can solder in a cap on CAP15 for his extra PSU and give it back to him. Of course that is not easy because it is surface mount and the connector is in the way. Still waiting to hear back from ituner.
Durwood summoned me over here for the challenge
What happens when you take the power INPUT wires for the PS and move them around? Does the noise change? AS LONG AS the chassis is sealed up well then noise SHOULD NOT get out. Does the chassis share car ground? If not, is it bad if it does? If so you could try to couple the computer chassis to the car ground with a good cap at a value that will pas 88.5-108 Mhz with little attenuation. One could also try putting ferrites on the power input wiring or even wrapping the wire or making a temp pigtail of a wire wrapped around something ferrous, if that works pull the metal and see if an air-coil will work. ALL PS's of this nature will make noise, we just want to contain it as much as possible noise within the machine is fine, lets not let it out.
Keep in mind that many car antennas that are not long, old-skool, masts are likely pre-amplified including most glass style, sans the old Chevy "windshield dipole." Make sure the preamp is energized, distance is key, keep any and all wiring away from the antenna lead and make sure that antenna lead is GROUNDED TO CHASSIS or it will attempt the force the unbalanced coax to become balanced and reception will go to hell. Ground is key on an antenna system and remember that RF ground and DC ground can be VERY different. For example cap coupling the chassis of the computer tot he car IS RF ground, but as you can imagine it makes a damn lousy ground at DC potentials.
I'll go back and re-read but I wanted to jump in and see if we can sort this out. RF can be goofy sometimes.
you reminded me of other things we did try in his car. We did take a ferrite and wrap the power wires through it. No change.
Cases: Both are wood. However mine has a perforated mesh cover, not sure if that would do some blocking of sorts. Cap coupling the computer chassis to the car chassis is going to be hard.
In my car, the antenna is not old school mast 33" style, but a shortly with a wire wrapped around it. Mine is not amplified because there is no power to it and I still get reception.
His car is a civic, and you know how noisy those civics are.
Ouch, wood case, regardless the PS should be metal right? Is that chassis ground?
It's tough to screw up FM to be honest, really easy to screw up AM, what's likely happening is that the interference is strong enough to de-sensitize the tuner!
FM works by frequency deviation, the amount of deviation of the frequency determines the audio, in fact modulation level is determined by the amount of deviation, whereas AM is simple amplitude modulation and modulation level is determined by the amount of signal strength over the carrier. So in order to screw up FM you have to either desens the tuner OR have SO MUCH noise that's broad banded that it completely wipes out any intended deviation that's getting in there. and if the latter is the case, that's pretty amazing, beyond noisy civic amazing
As for antenna amplification, does the stock stereo supply DC along the coax in a "phantom power" type of scheme? Have you ever had the antenna apart or have anyone from forums that can tell you if there are active electronics in the antenna base?
Now you feel me/us.So in order to screw up FM you have to either desens the tuner OR have SO MUCH noise that's broad banded that it completely wipes out any intended deviation that's getting in there. and if the latter is the case, that's pretty amazing, beyond noisy civic amazing
Well, let's assume we both have amplified antennas then that takes another piece out of the equation.
I think I'm lost now. IF it's amplified and it's NOT receiving power then your reception will flat out suck, maybe not in Chicagoland but it won't be pretty. AM will REALLY suck. Does the civic antenna look like this? (sans the XM antenna)
The civic antenna is part of the window disguised as defroster lines near the top of the window. Mine is about that length of yours but also has a wire wrapped around the mast. For the civic, there is a box in the passenger side c-pillar, two wires going from antenna to the box and then a two wire plug plugged into the other end. Box appears to be shielded and grounded via the mounting bolt.
We swapped M2-ATX's mine for his and even though mine has the CAP15, it still caused interference, so that isn't the problem either. I did not check mine because the HDradio was disconnected, but let's assume it would have worked fine as normal in my ride.
So get this though, he found an old school mast antenna in his shop, we used that instead of his window antenna no change UNTIL I was also touching the antenna portion, then loud and clear. I told him I could be his antenna at a small cost.
So it appears this is the problem-> combo of vehicle and power supply. I guess all the stars aligned to really screw this up. This is still no good, however there is hope if we can get an old school antenna to work. Any more thoughts? Bad grounding scheme of PSU? Bad grounding scheme for antenna (we tried a new ground point)?