HamRadioScience: Why Apple’s iMac May be the Best PC for SDR Applications

Over on on the HamRadioScience blog, the author has uploaded an article that makes the case on why Apple iMac PC’s may be the best choice for SDR receivers (at least for HF frequencies). In the testing he uses an SDRplay and Elad FM-Duo to show that the plastic case of the SDRplay does not affect the picked up RFI. He shows that when the SDR’s are connected to an iMac the interference from RFI on HF frequencies is minimal. However when connected to a Core i5 PC, there is significant amounts of CPU and monitor noise generated.

The differences in generated noise probably come from the fact that the iMac is probably much better shielded with an aluminum case and that they have high build quality standards for their monitors. The author suggests that an alternative to using an iMac could be to build your own PC, ensuring that dual chamber metal enclosures are used, which ensures that the power supply is isolated in its own separate steel compartment.

RFI is visible with the SDRplay in SDRuno when using the PC. But no RFI is seen with the iMac.
RFI is visible with the SDRplay in SDRuno when using the PC. But no RFI is seen with the iMac.

10 comments

  1. Johnny

    Nice article. I’ve experienced something similar with my Windows machine. i7 – 920 chipset. Whenever WSJT-X decodes, my graphics card will spin up (750ti), and i’ll see the waterfall in WSJT-X spike all over the place. The noise level bounces around constantly too during monitoring.

    On my iMac Mini, the noise level stays consistently at the same level & I don’t experience any spikes on the waterfall.

    • rengar :3

      Shit like that really grinds my gears:
      https://gyazo.com/938cef7d9d959ae66c2ab04d86242ad2 (Note: the antenna is about 10m away from my computer, on my balcony)
      It’s most likely my 760, because if i stress my GPU with e.g. FurMark, the frequency changes. (It could also be my PSU, Thermaltake berlin 630w, shitty psu, i know)
      I wonder if newer GPUs/PSUs also do that. I can’t find anything related to that.

  2. John B Cundiff Jr W3JBC

    Why not separate the ZDR dongle from the computer with a long good quality shielded USB cable. PUT the Dongle at the antenna feed run USB shielded cable inside to computer instead of coax ?:-)

    • Robert

      I must say that is a very interesting Idea . I am going to go today and pick up some shielded USB cable to put inside to computer . I like it , it’s brilliant .

  3. tb

    Really, you repeated this fairly non-technical explanation for less EMI with an SDR? I am very surprised, this site is usually very informative and credible.

    • Robert

      hi tb .
      I see that someones irish is up . You would be surprised how many newbies are out their and don’t know that much about radio electronics . This site is here for newbies as well for us oldies .

  4. August

    Man…….
    Is this blog is poisoned by the APPLE bees?
    Bro if you buy high end samsung or any other brand they have less noise.
    This test is like comparing cheap samsung model vs apple very expensive model
    of course apple wins
    If us true facts man not bias apple view.
    Compare by brand similar models etc

  5. Jenda

    I have seen USB optocoupler in a noisy SCADA environment. They seem to be USB1.1 only, though. No idea how difficult would it be to make a Hi-Speed one.

    Maybe just separating data and power rails in the cable and putting ferrite beads on them might help too.

    • Phelps

      If you read the article, you’ll see that they showed it to be coming in on the antenna, not the cables. The issue is the computer acting like a noise transmitter to the antenna, not internal interference.

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