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Thread: power supplies with minimal radio interferance?

  1. #11
    Car Audio Moderator durwood's Avatar
    Join Date
    Sep 2006
    Chicagoland (St. Charles,IL)
    First, I'm still not ready to blame the M2-ATX until all troubleshooting has been verified. I have an M2-ATX (don't know what revision level) and the Directed HD radio. I get reception, not quite as good as my stock radio, but it works. Stock radio reception is also unaffected by the PC and/or M2-ATX being on.

    nrgizer-was the PC in the car when you tried the standard ATX supply? How far away was the standard ATX from the actual car?

    will-this is a RF interference problem, not related to noise in on the audio signal. I think you are still getting confused about this.

    Does anyone know what the switching frequency of the PWM power supply in the M2-ATX is?

    Also, what cars are you guys having problems in? My friend that has this issue tried a standard ATX and still had no reception. I just talked to him about it. He even had issues with his GPS antenna not working in the rear of his vehicle where his PC was located. He had to fix that by moving the GPS up front. This was in a Civic.

    Also, does this happen with the car running, not running, or both?

  2. #12
    Constant Bitrate
    Join Date
    Jun 2006
    durwood, I've got a toyota corolla - euro model.

    The case I use is a Jye Jou Nu528 which came with a power supply. When i use this power supply i have zero reception problems. When I use the m2ATX with any combination of source power it screws up the reception. I'm convinced its the M2.

  3. #13
    Car Audio Moderator durwood's Avatar
    Join Date
    Sep 2006
    Chicagoland (St. Charles,IL)

    well my friend has tried a different supply and still had reception issues. A desktop PC also causes interference on an Alpine radio when located close to the desktop PC (standard PSU).

    Found some info I was looking for:

    The 3.3V and 5V rails operate at 300Hkz. The 12V rail works at ~500Khz and the -12V rail works at 100Khz.All inductors are shielded (closed magnetics) and the M2-ATX has 2 stage input filter, hopefully it will stay very quiet. Pre-scans conform with FCC/CE in the 0-30Mhz (conducted) and 30-1Ghz (radiated) emmisions.
    For something to disrupt reception through RF it would have to be in the same freq range. According to this, the M2-ATX should not have a problem with this. In most modern computers, CPU, FSB, RAM ETC can operate at 100MHz (x multiplier) however. Uh oh, this is in our FM band range. This is why I think it somehow has more to do with the PC than with the PSU. I cannot explain why it worked for you to change the PSU and problem goes away, but for someone else it does not.

  4. #14
    Constant Bitrate ronjon228's Avatar
    Join Date
    Dec 2005
    Grand Blanc, MI
    In my case I think it's my touchscreen that causes reception issues on my FM reception. I can't be sure though. Same thing though, FM radio reception is horrid with the PC on, once the PC is off, reception is great. You can sit there and watch the computer go into hibernate and the whole time static is rolling on my HU (in the glove box). Then AS SOON as the PC goes into hibernate, BAM full reception.

    Very strange issue. I'll have to turn off my LCD separate from the PC and see if that makes a difference. Haven't tried that yet because I pretty much got used to just having the PC off when I'm listening to the radio.
    1.8GHz Northwood, Intel 845 Mobo, 512MB DDR, 1x20GB + 1x160GB, Intel GPU, SB Live 5.1

    Sound System:
    Phoenix Gold RSD 65cs 6.5" Drivers, Infinity Tweets, Pioneer 305DVC 12", PPI Sedona 630IX, Alpine MRP-M500

  5. #15
    Constant Bitrate utd09bry's Avatar
    Join Date
    Sep 2007

    i'm having the same battle. i've had this issue since i first got my hd radio unit up and running and have never really figured it out.

    obviously the thing that i wish i could try is: a new mobo, a new power supply, a new case. seems to me one of those or a combination would end up fixing things..

    please keep this thread updated with any findings

    im running an M2-ATX and a Via VB7001 mobo in a Mo-Co-So case.

    i've tried split beads on the wires leaving the case, aluminum foil, unplugging all accessories, monitor powered down, powering the radio from the PC or from the HU stock connections, serial connection, USB connection, you can practically name it.

    i'd love to believe that i can just replace the M2 and my worries would be gone

  6. #16
    Constant Bitrate
    Join Date
    Jun 2006
    the opus isn't perfect, i lose radio text when i use the opus but its a damn site better than the M2.

  7. #17
    Constant Bitrate utd09bry's Avatar
    Join Date
    Sep 2007
    I bought a power inverter today and tried out a regular old ATX power supply in the car.

    I was able to tune and stay steady-locked onto many HD signals without much problem. Some stations without HD had a little bit of static, but to be fair I had my computer laid out in the back seat.. out of the case and everything, in order to attach the PS.

    So, this easy and maybe not 100% definitive test showed me that the M2-ATX seemed to have created quite a problem in my install. Unfortunately there are still a lot of factors and variables involved (technically, I relocated the PC slightly during testing, and I dont know what kind of filtering might be involved with the inverter I bought).

    In any case, I would love to test out another DC-DC PS. I might see if I can get my hands on one.. I'll keep this thread updated... others, please update on your own progress!

  8. #18
    Variable Bitrate
    Join Date
    Mar 2004
    Quote Originally Posted by utd09bry View Post
    Thanks for the update; I've been waiting for a normal desktop ATX power supply in the mail (for another computer) so I haven't tested my install yet

  9. #19
    Join Date
    Mar 2008
    Quote Originally Posted by dyne View Post
    My m2atx no longer survives cranking, so I figured I'd get a new power supply and hopefully fix my radio reception problem (I can't get any radio stations with my carputer on). I already have the carputer fully enclosed in an aluminum Mo-Co-So case, but that doesn't block the radio interference.

    Are there any power supplies out there that don't really interfere with the radio?

    I noticed my M2ATX stocked surviving cranking this winter; and next thing I knew I needed a new battery. If might be your battery can't keep the voltage high enough on a crank.

    I am highly suspicious of my M2ATX. I am think about getting an Opus.

  10. #20
    Car Audio Moderator durwood's Avatar
    Join Date
    Sep 2006
    Chicagoland (St. Charles,IL)

    So I visited my friend who was having the static problem, this time he really had tried a desktop PSU and found that he could get reception (don't ask). Sorry for not believing the PSU was causing it. He also had another M2-ATX that we did some testing with.

    1) With only the M2-ATX powered up, a little bit of static, reception got worse but was still getting stations.
    2) Loading down the power supply by actually powering up the PC, reception completely killed. Makes sense, whatever is happening occurs as the supply is forced to create more power.

    Now we had verified that the M2-ATX infact creates interference in the FM radio band. But, why?

    My car also has same tuner and M2-ATX although my M2-ATX is older by about 2 years.

    So the only two different factors are

    1) Older vs newer M2-ATX
    2) My car has external antenna, his has an in the window glass antenna (amplified).

    He did not have a good external antenna to try, so we could not rule that out. But I did wonder about the M2-ATX versions. Digging up the changelog:


    01/15/2006 Production release
    01/15/2006 Firmware release 1.1 (from M1-ATX)
    04/15/2006 Rotate 12V ATX connector (mechanical issues)
    04/15/2006 Connect R33 pull-up to VLIN5 instead of VCC
    09/15/2007 Firmware release 1.2: Timing changes for PS_ON, 5VSB ON-delay
    05/17/2007 Firmware release 1.3: Fixed PWR_OK delay at shut down
    06/23/2007 Change R24 to 46.3k (12.05V output), fixed 12 V rail over-shoot
    08/10/2007 Removed C1, 5V rail fix
    08/10/2007 New PCB UL number UL mark: E154554
    08/10/2007 Introduced serial number sticker UEC07xxxx and higher
    06/06/2008 Serial number UEC0819xxx and higher
    06/06/2008 C41 (was 10nF) 15nF X7R 10% 3.3/5V startup timing fix (6-26V)
    06/06/2008 C35 (was 10nF) 22nF X7R 10% 3.3/5V startup timing fix (6-26V)
    06/06/2008 Put back C15, 0.1uF X7R 10% 3.3/5V startup timing fix (6-26V)
    06/06/2008 Firmware 1.4: Shut down while ACPI is not fully up fix via 60 second AutoLatch feature
    06/06/2008 Firmware 1.4: Officially introduce3 more timing schemes:

    0001 10 minutess / 1 hour
    1001 15 minutes / 2 hours
    0101 1 hour / 1 hour 15 minutes
    NOTE: These changes were availabe in firmware version 1.3 but never advertised to the public.

    06/06/2008 Firmware 1.4: In P0 (dumb PSU mode) if ignition is used, can act as an UPS system.
    (consult M2-ATX product page for more information)

    ================================================== ===
    06/18/2008 Extended availability for the next 5 years
    ================================================== ===

    06/26/2008 Serial number UEC0819xxx with silver mark or serial number higher than UEC0822xxx
    06/26/2008 Changed C35 to 15nF
    06/26/2008 Removed C15 in order to prevent rare cases in which 5V starts oscilalting at startup.

    11/01/2009 Serial number UEC0850xxx and higher (m2-ATX, M2-ATX-HV)
    11/01/2009 changed C15 to 0.1uF X7R 10%, revert to change made on 06/06/2008
    I figured that since my power supply works fine, there must be a filtering issue and low and behold cap changes and oscillating problems are noted. I looked at his power supplies, both were missing cap C15, mine has Cap C15. It is located nearby the 4 pin 12V connector. Interesting.

    I'm contacting the company who makes these PSU's to see if I can get more info from them.

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