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Author Topic: Whats the rub with switching power supplies?  (Read 2954 times)
KE4JOY
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« on: August 02, 2013, 11:43:56 AM »

I've been shopping for a 20-40 amp 13.8 power supply. Been doing a little reading and often see "avoid switching psu's" they will make your receiver scream and holler!

Is it really that much of an issue?
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KS2G
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« Reply #1 on: August 02, 2013, 11:51:16 AM »

A myth that just won't die.

For routine HF operating, good-quality switching supplies do not cause receiver hash problems.

I use two MFJ-4225MV switchers and never hear a peep out of them.

73,
Mel - KS2G
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K5LXP
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« Reply #2 on: August 02, 2013, 11:53:42 AM »

It was an issue about 20 years ago.  It will take a long time to erase that memory from the old tiimer's minds.  Nowadays it comes down to the application - whether you want light and compact but likely will come with a fan, or heavy, large and no fan.


Mark K5LXP
Albuquerque, NM
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KE4JOY
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« Reply #3 on: August 02, 2013, 12:08:05 PM »

Why did the 'issue' go away? Is it because of better receivers or better psu's?
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N4NYY
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« Reply #4 on: August 02, 2013, 12:34:15 PM »

Why did the 'issue' go away? Is it because of better receivers or better psu's?

I do not know, but in the late 1980's and early 1990's they failed or squealed with regularity. They are much better now.
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AD4U
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« Reply #5 on: August 02, 2013, 12:52:19 PM »

Most switching power supplies today are relatively "quiet".  Some of the older ones spewed various amounts of RF hash all over the radio spectrum, making receiving weak signals rather difficult with one of them nearby.

If a switching power supply fails, they are a lot more difficult for the average HAM to trouble shoot and repair when compared to a linear PS.

Dick  AD4U
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W9GB
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« Reply #6 on: August 02, 2013, 12:55:10 PM »

Quote from: KE4JOY
Why did the 'issue' go away? Is it because of better receivers or better PS?
Switch-Mode Power Supplies (SMPS) have been in US residential homes since mid-1970s.
Sony built some of the first for Steve Jobs/Steve Wozniak's Apple II computer.

These early "first generation" units were well-made and good quality (Japan).  
Radio Frequency Interference (RFI) was a minor problem.

The problems, that I experienced first hand, cropped up in late 1980s and throughout the 1990s with new low cost mfg. in Taiwan and mainland China.  Filtering parts omitted from PC boards, low quality parts used.  This resulted in high failure rates, and widely reported RFI issues (noisy, not usable around radio receivers).

My hospital staff found an issue (leakage and RFI) in new Compaq computers (1993) -- that forced a recall of those defective units as well as warnings listed for hospital users to vigilently check units.  That SMPS supplier was discontinued.

Stick with name brand products, where you can return a defective unit under warranty.

BTW, I use both linear and switch-mode power supplies.  I can easily repair the linear PS for a few $ (unless transformer bad), the switch-mode is NOT economical for major repairs (availability and cost of parts) - capacitor leakage/replacement being exception.
« Last Edit: August 02, 2013, 01:01:14 PM by W9GB » Logged
AA4PB
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« Reply #7 on: August 02, 2013, 01:01:20 PM »

The newer supplies are much better, but I don't think the problem has completely gone away. What you hear in the receiver depends on how much noise is being radiated by the power supply, how far away your antenna is from the power supply, whether you have any common mode issues with the antenna feed line, and what frequencies you are listening to. These variables are why one person will complain about the switching noise from a particular supply while another will use the same supply and tell you that it is perfectly quiet.

If you really want to test one, connect a piece of wire to the antenna jack on the receiver and run the wire along the cables coming out of the supply. Then tune around the lower bands and see if you detect any hash. If you don't pick anything up that way then it should be good with most any antenna installation.
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W5GNB
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« Reply #8 on: August 02, 2013, 01:29:38 PM »

Be careful of the China built stuff, those will still EAT your receivers....
The USA built stuff works well and I have had No problems in years....
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WB2WIK
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« Reply #9 on: August 02, 2013, 02:44:01 PM »

It's still a variable, I've found.

Some of the power supplies sold specifically for the ham radio market are very quiet and generate little to no noise in the RF spectrum above 1 MHz.  But they're not all wonderful, and when the ARRL Lab tests power supplies, they always report on this, with a graphical representation of the RF noise output from switchmode power supplies.  They've found some "stinkers," even pretty recently.  Most are pretty good.

Some of the power supply "bricks" used on laptop computers and similar devices are pretty noisy (even today in 2013) and can generate RFI that can be heard in the HF spectrum by sensitive receivers like we all use.  The switchmode power supply "wall warts" and "bricks" used on some network switches and routers are terrible, even today.  High-end brands that cost a bit more are usually better.

Apple has done a good job IMO on most of their products.  Not everyone has.

The ARRL Lab reports from their Product Reviews are pretty interesting, and all on line.
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WB2EOD
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« Reply #10 on: August 02, 2013, 02:53:15 PM »

Astron or Samlex.  I own one of each.  Both good and quiet

73
WB2EOD
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WX7G
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Posts: 6136




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« Reply #11 on: August 02, 2013, 03:23:43 PM »

Linear power supply:
Quiet, usually no fan
Inefficient
Large and heavy
Easy to repair
No RFI
Price is about the same as a switching power supply

Switching power supply:
Fan noise, usually has a fan
Efficient
Small and light
Often not repairable, disposable
Potential for RFI
Price is about the same as a linear power supply
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AC4RD
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« Reply #12 on: August 02, 2013, 03:39:55 PM »

I've had both over the years; I have never had a switching PS that was a problem for HF/6m.  They're light and I think they're more efficient than linear supplies.  Certainly easier to carry around, too.  :-)  If you GET a switching supply that has bothersome noise on your bands, you can always use it as a backup or something.  Switching supplies make sense to me!  --ken
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NO2A
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« Reply #13 on: August 02, 2013, 03:49:58 PM »

As great as the linear supplies are,I can`t see using anything else. There`s simply no reason to.
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N4NYY
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Posts: 4800




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« Reply #14 on: August 02, 2013, 04:06:25 PM »

I have a linear in my shack. If room is an issue. Get switching. If portability is an issue, get switching. Otherwise, get a linear. They are reliable and easy to fix.
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