Switching Power Supply Hash - Questions

Discussion in 'General Technical Questions and Answers' started by KB3MOW, Sep 19, 2019.

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  1. KB3MOW

    KB3MOW Ham Member QRZ Page

    I'm convinced! No cable-cutting here. I have the PS about 3 feet from the rig and can move it to about 4 feet.Any farther than that and I have to put it in the closet!

    I've been lucky with computers & monitors. My old CRT did throw some junk, but only when the display was very light. Had to change all my background colors in Excel! Now I have a 20" and a 24" LED monitors and get no interference from them.

    Tnx Mario es 73
    Dave - KB3MOW
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Unless the power supply is radiating directly through its case and your rig is unshielded by anything, proximity of power supply to rig usually doesn't matter because it's the antenna, not the rig, that's picking up the interference (noise).

    DC power lines could be radiating, but it's more common that the AC power cord is conducting RFI back into household wiring, so the "radiating antenna" is everywhere.

    A good AC power line filter might help.

    My lab used to perform EMC testing on everything including power supplies, and those included radiated emissions, conducted emissions, and electromagnetic immunity (the latter of which was never required by FCC, but was and still is required by CE for Europe) and some switchmode power supplies were absolutely excellent while some were really terrible. Most, not all, of the really terrible ones came out of China. But that was also 5-10 years ago, and stuff changes.

    It was interesting "back then" when we had an FCC certified EMC lab (which we have since sold since we didn't really need it anymore -- we sold it to Keystone Compliance in PA, who now runs the same lab from back there) that when it came to the Chinese products, if the manufacturer submitted test samples they were often just fine, but if we purchased exactly the same products on the market via Amazon.com or wherever, they were not just fine and failed the tests. The difference was the manufacturer-submitted samples included critical RFI-reducing components which have real cost, while the "market purchased" samples lacked exactly those components.:p
     
    WA7PRC likes this.
  3. N8VIL

    N8VIL Ham Member QRZ Page

    I cleaned up my Samlex switching supply (SEC-1223) switching supply considerably by using three 1.5 uF @ 100 volts polyester film capacitors. I placed 1 across the positive and negative terminals. I also placed 1 on the positive and 1 one on the negative terminals to chassis ground. Possibly may work for your power supply. The birdies are almost gone.
     
  4. N8FVJ

    N8FVJ Ham Member QRZ Page

    Like I said, why do you have to clean up a power supply that the extra parts costs money and your time screwing with it. Buy an Astron linear type power supply- No filter and other accessories required. Done deal.
     
  5. N8VIL

    N8VIL Ham Member QRZ Page

    I had 3 given to me with bad filter capacitors that I repaired. They were free and were worth my time and a couple bucks. I would never purchase one new as a power supply for my main rig.
     
  6. KG7FIU

    KG7FIU Ham Member QRZ Page

    Had bad luck with MegaWatt P/S supplies myself, but there could be different factors involving your configuration, so it might be unfair to characterize anything.

    Might suggest you simply borrow a more expensive power supply -- and then run a simple A/B test using your radio. That should tell you all you need to know -- about how good your MegaWatt is (or isn't).

    Good luck.
     
  7. N8FVJ

    N8FVJ Ham Member QRZ Page

    I would not use a used switcher on my 1000 dollar transceiver.
    I would never use a junk power supply supplying DC to my expensive transceiver. I also do not know if the junk power supplies have an overvoltage crowbar in the event of a voltage regulation failure. Buy a good linear power supply and use it for the next 40 years- done deal. Cost per year is less then $5 for a 35 amp power supply. I have an extra $5 per year.
     
  8. N8VIL

    N8VIL Ham Member QRZ Page

    I would not use "junk" power supplies either. Samlex happens to be one of the better quality switchers. Properly repaired they are a decent unit. They also made power supplies for OEM companies.
    I have repaired many power supplies in over $1000.00 rigs (at the time of when they were purchased new by someone) that are mains powered with internal switching power supplies and worked fine. Many of the Icom internal power supplies that I rebuilt were nothing more than Icom PS-30 supplies mounted inside the radio.
    I agree that a linear power supply is the way to go. But if someone has a switcher and is a decent unit there are ways to clean up the output and make it a viable option for them. I have a nice Astron. I also have an "El Chepo" 20 amp linear that has no crowbar protection. (Pyrmaid). I wouldn't trust it to power anything but a light bulb. I use it for electrolysis rust removal and electroplating.
     
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The advantage of switchers is size and weight; I use only big, linear power supplies at home ("shack" supply is an RS-70M) but how would you pack that in a suitcase for air transport to operate somewhere not near home? You really can't. Too big, too heavy. A 50-70A switcher can be half the size and 1/4 the weight.

    At "home," for a ham station I don't bother with switchers, either. We all have enough of them running in appliances all over the place! And one of the problems de-bugging RFI is some of those switchers are never shut off until you literally unplug them from the wall outlet; just "turning them off" often doesn't really turn them off -- it just puts them in "standby" mode, but they're still working. Any appliance that has a remote control to use it, which allows powering it on and off via a remote, is never really off.
     
  10. N8VIL

    N8VIL Ham Member QRZ Page

    Whenever I get on the radio, I have to go to the kids rooms and unplug their stuff to get noise to go away. Video game power supplies, phone chargers and such. I built a linear supply for my wife and myself to charge phones and tablets and has a crowbar circuit that shuts it down with anything over 5 1/2 volts. Need to make a few more for the kids. I have a SM car battery charger that makes broadcast radio reception impossible when in use.
     

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