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Thread: power supplies with minimal radio interferance?

  1. #191
    Maximum Bitrate Mickz's Avatar
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    Hi, thanks, the case is homemade, you can jump on it. The PSU is mounted inside the case in the box on the right of the picture.

    There is not much you can do except do as I have and put the PSU inside a box with feed-through caps. The PSU case must not be made of steel, use copper or you can use aluminium if using bolt in feed-through caps

    Steel has a high surface resistance at higher RF frequencies. Short meaning: You get RF voltages developed across the case, it radiates.

    Nothing much you do with CPU frequency will help. Itís the wave shape or fast rise time (square wave) of digital signals, CPU clock, data lines and PSU inverters that produce broadband harmonics content. Changing MB frequency may shift a beat/mixing frequency that appears in the FM band, but will do little for the de-sensing hash that makes clear reception difficult.

    Just Putting the PSU inside its own case, without feed-though caps on the leads, will do little.
    Itís not radiation from the PSU board itself; itís from the cables connected to it.

    The case with feed-through caps bypasses this crap from the lead exit/entry points into the very low impedance earth formed on the inside of the case, with no way for the RF currents to transverse through the wall of the case.

    Finally, placing the MB and shielded PSU into this aluminium case made a small but measurable improvement to the final noise level. Iím just blown away by the noise improvement in this system.

    From no GPS ďnot even one satelliteĒ to wall to wall signals. From almost no FM except for one local station to every weak signal FM station with no interference

  2. #192
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    Sounds like a project for the near future....I'll definitely need a smaller case though. I'll have to take some measurements of where it will go up behind the dash. Did you use anything special to bend the aluminum?

  3. #193
    Maximum Bitrate Mickz's Avatar
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    No bends just aluminium angle strip and self tapping screws. Off the shelf at my local hardware.

    BTW if you mount the PC in the dash, donít plan on using a GPS receiver in the front of the car; at the very least you will have poor satellite levels Ė which may be ok until you get into a bad sat location. FM was Ok though after the PSU mod, but its perfect now with the PC relocated to the trunk.

  4. #194
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    so even after the caps and casings...you still get bad GPS signal? crap. I was trying to avoid the long cable runs with my pc in the trunk....I might just get different/better cables and leave it in the trunk.

    The way my setup is now, I get the fm signal degradation...but the GPS signal is extremely high...near perfect. The GPS receiver is located in the very front of the dash behind the security light (so it's really inside the dash) and about 2" below the windshield. The pc is in the steel travla case in the trunk...and the radio antenna is embedded into the rear window...that's probably why I have good gps signal, but poor fm right?

  5. #195
    Maximum Bitrate Mickz's Avatar
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    Yes, my GPS receiver is in almost the same location. In my case moving the PC to the trunk did not "completly" fix the GPS. In my earlier post I mentioned how variable this is with car wiring, voltage, cable layout and the wind. The PSU mod finally fixed the GPS.

    I was concerned with Video, however a good quality 5m cable gave no change to the video quality, of course this may depend on the video card output circuitry. In the end all you can do is try a test setup and see how the GPS runs, you may get lucky.

  6. #196
    Variable Bitrate
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    Yeh, for my computer, its located between the two front seats, underneath the storage bin inside the centre console (Tucked in around the back of the handbrake!).

    I get perfect gps reception, with the receiver in the bottom right hand side of the front windscreen, but I get average, noisy reception on the Directed HD radio (AM/FM only, I'm in Aus!) which is located in the centre of the dash, right where the OEM radio sat.

    So for me, I think there is enough shielding (My body, the steering assembly and some huge crossmembers inside the dash) between the computer and the gps, but only 2 layers of plastic between the computer and the radio.

    Which really does show how variable this is, I remember seeing an article by an antenna engineer, who said its almost a black art rather than a science, and while they can design a system that "SHOULD" work, sometimes it just takes an engineer tweaking things slightly to make a massive difference in how it works.

  7. #197
    Raw Wave
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    Woosy engineers. Antennae are well understood.
    Batteries are a black art. Or at least grey. Lead-gray.

    The only black art with antennas is everything around them - like ground-planes, static, noise (electrical, EM, sun, atmospheric, communications...), obstructions, reflections, doppler, cross-modulation....
    And that can be ascertained for a few thousand dollars for that day, that weather, that location, and only those conditions.

    That's not a black art - that is called "fluke" or "luck" or "coincidence". (More so with with there associated blind-, bad- and unfortunate- adverbs or adjunktive adjectives <whatever> respectively.)

    Injuneers! What would they know? (And did they ever know it?)
    Engineering is nothing but black humor. (Though being into batteries, I now have a grey taint.)

  8. #198
    Variable Bitrate
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    Just wait till someone comes up with a battery powered antenna. It could be even more devastating than the LHC, we might just see the end of civilisation as we know it

    And are you sure the grey taint isn't just the hair on the noggin Spark?

  9. #199
    Raw Wave
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    How dare you suggest grey hair!

    What - you think I am one of those half-greys - you know, the type that uses that advertised hair dye so they are both young (energetic LOL!) enough and experienced enough to get the job? (Yeah dudes - keep some grey! )

    Nah - I'm the full pinko.... Now turning redo for the later browno and cancero.



    But battery antennas - I've had a few.... they're great!
    For a bunch of alleged wooses, they design great stuff!!! (I swear by my GFs powered PhaseLink antenna for TV, and my old active car antennas were pretty good.)

  10. #200
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    Quote Originally Posted by Chester View Post
    Cool, I'm happy to spend more on the more expensive ones, even allowing for around 10, thats still not a huge cost overall, for what sounds like a huge improvement.

    I will mount a strain relief on the outside cable to remove any chance of me yanking the cables off the caps, that will be easy enough to do, and should also make it look neater, as I can use shrouding on the cable to make it look all nice and pretty, and tie that in with the strain relief tiedown.

    Awesome, got a few evenings of fun ahead of me now, I'll post up how I go! hahah
    so any progrees of this?I will propably make my self the mod too but i must find a how to with good pictures.Can anyone help me about the soldering on these capacitors?I believe from what i understand here i need 9 capacitors 1000pF feed thru 200v or 500v correct?Mickz if you have better pictures that would be very big help.Thanks

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