Thread: power supplies with minimal radio interferance?

Wow great news - Looks nice. I had it easy as I had some high current case mounting bolt-on caps so was just a matter of drilling a few holes and soldering the leads. If you use any form of GPS did you notice any improvement? FM went from nothing to really good as well but GPS and DAB also showed huge reception improvements.

I'm using a Navilock NL-402U GPS (U-Blox 5). It is actually mounted in the dash just above the M4-ATX but I did not have reception issues.
Signal strength seems a tad better now, though.

FM reception while driving is okay although stereo reception is still a bit noisier than my stock radio.
DAB is crystal clear. Looking forward to the commercial radio stations going DAB+ later this year.

Originally Posted by TBM

Mickz, big

With your information I just finished my M4-ATX mod.
FM reception was almost non-existent and now I'd say it's at least good.

Helluva job to mod, assemble and solder everything but definitely worth the effort.
btw I did not combine any wires. Each wire got its own ceramic FTC.

Great work

x2!!

As to Mickz' work - what can I say - amazing!
He might be the only Aussie remaining that gives our "clever country" any credence! (Though IMO many ways true, that is more a dig at political lip-service. But certainly. my hat off to Mickz's amazing capabilities and posts!)

Me too!

Finally got it into the car for a test drive. No dropouts on DAB during the drive and good signal (around 55-60%) under the Iron Cove bridge in Sydney. I had 0% signal before.

No pictures as it currently looks like a dogs breakfast. Need to finish off a few items and make a hole for the fan in the lid. But it worked!

Thanks again to Mickz for all assistance and help!


JJ

Just got back to the PC.

JJ, great to hear you had a decent improvement in reception. Its ridiculous that we have to go to all this trouble because most manufactures only play lip service to spurious RF noise pollution.

OldSpark, as usual thanks for the kind words.

just wanted to add some flame on the M4 ATX. no need to mention that when it works, there are no FM anywhere near it.. BUT my problem is bigger.. it induces huge noise in the system, which crosses to my screens , as screen hummin... its driving me crazy. if i power the pc on my house from a 12 v supply, the problem remains. But i dont think its the EMF, because, if my carpc is working, and instead of plugin the vga of the screen to my pc, i plug it to a laptop, there is no humming... any ideas how i could get rid of that?? i just recently bought the ATX and its quite frustrating!!

There are a few transmission paths for noise in a system. The PC and PSU can radiate a small amount of RF but this is minimal compared to the noise that radiates along the length of every cable attached to the PSU or PC. This is why you can power the screen separately from the vehicle and hold the cables close to the M4 and not see the same interference. Some of this noise propagates along the cables more so than coupling between them.

I have never encounter noise in the 8" LCD I use under any condition, 15 foot VGA cable or HDMI to VGA which I currently use. Some monitors are very poor at rejecting noise or are susceptible to noise due to the design of the input stage and conversion/driver circuitry.

When people talk about earthing or grounding of audio equipment and external devices they usually think in terms of DC grounding requirements. Short lengths of 8 gauge cable would be the minimum starting size for noise and ground loop elimination with 4 gauge being the norm. It has nothing to do with current capacity of the cable and everything to do with the impedance of the cable at the offending noise frequencies.

The only way to remove noise from the M4 that is interfering with FM, DAB or GPS is to place it into an RF shielded case with feed-through caps on every lead.

However this may not be needed for Audio noise.

The first thing that needs to be done is to use high quality twin sheathed double shielded audio cables between the PC and the AMP. These cables are around 1/4" thick per channel and have a double shielded (foil and braid) inner cable encased in another outer shield of foil and heavy braid. This is the only true method to eliminate the ground loop (when using this audio setup method) between the Audio source (in this case a PC) and the Amplifier input stages and thereby remove the noise that develops across the interconnect cables. Ground loop isolators mostly work but can reduce low frequency response and cause other undesirable audio effects depending on the quality of the device. A 4G cable between the AMP and the PC can also help and both the PC and the AMP can and usually should be grounded to the Vehicle chassis.

The vehicle chassis CAN (with reservations) be a good DC ground between two or more points, it is a useless (high impedance) ground at higher frequencies and especially so at RF.

The biggest source of noise in the audio system are usually the Line and MIC input stages of the PC. Once again this is a complex interaction between the noise generated by digital circuitry on the Mother board and the digital noise from the PSU and other devices. The only effective low cost way I have found that almost always works is to run an 8G or 4G cable between the tin earth shield surrounding the input sockets on the Motherboard and the external audio source ground.

A special note with the M4, when you start the vehicle the noise often changes in pitch or severity, to simplify, this is the M4 going from regulate to boost modes on the 12v rail as the M4 input voltage tracks the alternator charge voltage.

Also note that some users with an M4 can experience almost no noise in their particular installation.

Finally back to the screen, a quick low cost thing you could try is a 4G ground lead between the LCD ground and the M4 or the PC VGA ground (or both - M4 to PC VGA and then to LCD) The noise may be getting into the PC VGA circuitry or travelling up the cables to the LCD input (or both) - too many paths and unknowns to give a definitive answer, again some monitors reject this noise by design or luck.

so, would a RF shield box, solve the problem, or we cant be sure? cause i have prety much tried everything else.. + noise from mic in is not the case, since before M4 atx, i didint had any noise!