Switching Power Supply Hash - Questions

Discussion in 'General Technical Questions and Answers' started by K1DJE, Sep 19, 2019.

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  1. SM0GLD

    SM0GLD Ham Member QRZ Page

    I have a schaffner dual stage main filter.
    It can very often eliminate all noise comming from the AC side.
    I have it in a box when I am on RFI hunt.
    I donĀ“t use it as soon the problem is solved.
  2. SM0GLD

    SM0GLD Ham Member QRZ Page

    I found a schematic.
    If this is your PS there is no filter on the DC side.

    Attached Files:

  3. K1DJE

    K1DJE Ham Member QRZ Page

    Mike, thanks for the info. I guess I'm not surprised by the lack of filtering. Buy cheap, get cheap. But I got what I was able to afford, so now I need to address the issue. Ferrites are a relatively cheap fix so that will likely be my first step on the DC cables. At least this isn't keeping me off the air as it's only on 80 & 160, but with low-band season getting close I want to fix it quickly.

    Clif, I appreciate the 'scope suggestion but I don't own one. I can see the problem visually on any of my digital waterfalls, and can see exactly what happens when I transmit. The load on the PS causes the hash to drift.

    Thanks for all the input!

    Dave - KB3MOW
  4. KT5WB

    KT5WB Ham Member QRZ Page

    I need something like that. Does it look something like this, except with an RF connector to your rig in place of the meter?

  5. SM0GLD

    SM0GLD Ham Member QRZ Page

    Yes exactly! but only one turn pick up coil is needed.
    I have one ferrite with a fairly large hole to go around fat cables.
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    There are a few switching supplies that have a variable frequency PWM oscillator adjustment on the front panel.

    You can move the switching noise off of your operating frequency.

    Chances of a switching supply having zero noise across the radio spectrum is slim.
    SM0GLD likes this.
  7. SM0GLD

    SM0GLD Ham Member QRZ Page

    If we look at the s-400 schematic it would be possible to add that feature by replacing R17 with a pot.
    I would aim for +/- 2-3 kHz variation maximum on the fundamental frequency.
  8. K8ERV

    K8ERV Ham Member QRZ Page

    Just put the hash in a skillet with some butter----

    TOM K8ERV Montrose Colo
    SM0GLD likes this.
  9. ND6M

    ND6M Ham Member QRZ Page

    and throw in some okra, butter, salt, pepper, cook it all up.

    throw it in the trash can,

    eat the skillet
  10. KA2IRQ

    KA2IRQ Ham Member QRZ Page

    Don't go cutting cables too quickly. I had a similar problem with a power supply and the RF was not coming from the cabling, it was coming from the well shielded case of the supply itself. With long enough wires, the problem was solved by moving the power supply far enough away from the radio that the radiated "hash field" no longer affected the radio.

    I originally thought I blew out a filter cap in the supply, because it was never a problem in the past (old station had them separated, new layout had them closer together). There's something to be said for separating DC power equipment, computer equipment, and radios.

    Heck, everyone told me my computer monitors would not interfere with my HF rig.

    Uh huh. Worst noise generator in my station is my computer monitor. One generated hash from 3 to 30 MHz, the other just generates birdies every 30 KHz. PITA.

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