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More cheap switching power supply hash woes

Discussion in 'Ham Equipment' started by Moleculo, May 19, 2015.

  1. Moleculo

    Moleculo
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    My previous article on the topic of cheap vs. quality switching power supplies, I demonstrated the amount of hash generated in your HF rig with pictures from my panadapter display. After that article, I shelved the cheap Chinese supply and didn't look back. Unfortunately, the old power supply powering my D-Star UHF home repeater died, so I decided to put the cheap switching supply back in service. What a mistake.



    The following panadapter screen captures show the amount of hash being generated by the cheap supply that is being picked up by my Elecraft K3 transceiver which is 4 feet away. In each pic, I powered on the supply and let the waterfall scroll a bit before taking the screen pic so you can see a some before-and-after.

    The first pic is 75/80 meters, The arrow points out one of the frequencies where the hash is present:
    [​IMG]

    This pic is 40 meters. On this band, the problem is not as bad, but it's still there and you can still hear it when dialing by:
    [​IMG]

    Some have commented that they don't hear the hash on 10 or 11 meter radios. The following pic is 10 meters, and as you can tell it's here, too.
    [​IMG]

    In each pic, you can see that the RFI hash repeats every 30khz or so. At its worst, it sounds like a moving tone carrier; at its best it raises the noise floor enough to be annoying. As soon as I can get a new supply, this thing is going in the trash. To prevent any confusion, this is the supply used in these pics:

     
    bob85 and Robb like this.

  2. ButtFuzz

    ButtFuzz
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    "You don't get much for a dollar anymore!"

    -- my grammy, now deceased, back in the day when viewing some scantily clad young ladies at Myrtle Beach, SC.
     
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  3. Moleculo

    Moleculo
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    Yesterday I changed out the cheap power supply for a 30 amp Megawatt and the interference to my nearby HF rig is gone. Not a peep and can't see anything on the panadapter. As a side benefit, the fan speed is much more civil on the Megawatt supply; the other one was always running full speed when the repeater was transmitting, driving me crazy.
     
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  4. Jay in the Mojave

    Jay in the Mojave
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    Hello Moleculo: Impressive article there showing the before and after HF Band Spectrum Measurements, of EMI from the clone power supply. Good going.

    Had a ham type power supply generate a noise on a local UHF Repeater frequency, the EMI signal drifted in and out of the monitored frequency. A few bypass caps and choke in the AC line fixed that.

    I am told that switching powers supplies should be used close to their current rating. To keep EMI noise down. But never tested this, do you see any different noise floor levels under min / max current loads of the Megawatt Power Supply?

    Jay in the Mojave
     
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