I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding
24V @ about 300mA.

Are switch-mode powers supplies alright or are they too noisy to be used for
receivers? TIA.

On Mon, 28 Jan 2008 11:27:20 -0000,
Richard wrote in
:

I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding
24V @ about 300mA.

Are switch-mode powers supplies alright or are they too noisy to be used for
receivers? TIA.

Some switchers are very good, some aren't very good at all. One friend
has the Icom PS-120 (I think) for his Icom transceiver, and finds it
to be so noisy as to be unusable .Other friends have other switchers
and find them to be OK, and a third group find them somewhat noisy,
but tolerable if you don't mind tuning around the birdies.

I use a Samlex 30-Amp switcher to drive my Yaesu FT-897D in the shack,
and it's just fine above 500 KHz or so. It *does* put out some hash in
the 20-500 KHz region; my SDR-IQ receiver's waterfall display shows it
quite plainly.

You may find a linear-mode supply (xfmr; half-wave, full-wave, or
bridge rectifier; filter) to be better for your use; I don't know of
a lot of 24V switchers. Certainly a linear supply will be quieter if
done well, as the only noise will be from ripple that gets through the
filters, and the tiny bit of hash from the rectifier junctions turning
on and off.

--
I had the largest, strongest tornado ever recorded march by just four
miles away in May of '99, I could feel the house breathing from the
subsonic pressure wave. It's a Live Thing, like Fire.
-- Charly the *******, in rec.org.sca

On Mon, 28 Jan 2008 11:27:20 -0000, Richard wrote:
I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU
feeding 24V @ about 300mA.

You are almost talking about a wall-wart there, aren't you?
Or, possibly, a desktop 'brick' PS.

Are switch-mode powers supplies alright or are they too noisy to be
used for receivers? TIA.

Just make sure the PS is enclosed. And, use ferrite beads/doughnuts on
_all_ input\output wiring. And, it wouldn't hurt to put .001 uF bypass
capacitors on that wiring, too, betwix the ferrites and the PS.

My venerable IC-551's (6M) internal power supply went kah-kah and I
replaced it with a switched-mode PS from Marlin P Jones:

http://www.mpja.com/

That was some time ago, but what I bought was similar to:

http://www.mpja.com/prodinfo.asp?number=16001+PS

My original requirement was _size_. I wanted to stuff the new PS into
the same cavity in the IC-551 where the old PS came out. So, having
installed the new switched-mode PS _inside_ the rig -- with all the
install 'details' I listed above -- I saw no appreciable rise in the
no-antenna-connected noise floor.

Plus I could 'tweak' the output voltage -- setting it at 13V -- and "amp
up" that IC-551 to a blistering 11W or so. HI!HI!

I encouraged a feller in Kansas to do likewise with his IC-251 (2M) that
had a dead PS, and he reported similar success.

Of course, YMMV
gl es 73
Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
*** Killfiling google posts: http://jonz.net/ng.htm

On Mon, 28 Jan 2008 11:27:20 -0000, "Richard"
wrote:

I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding
24V @ about 300mA.

Are switch-mode powers supplies alright or are they too noisy to be used for
receivers? TIA.
Some are, some are not. You have a lot of choices available at 300ma.

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"

On Jan 28, 3:27 am, "Richard" wrote:
I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding
24V @ about 300mA.

Are switch-mode powers supplies alright or are they too noisy to be used for
receivers? TIA.

The receiver I'm building uses switchers internally to take 5V down to
various other voltages. Total power supplied by the switchers is
around 20 watts. They're little open modules. I can "see" the
fundamentals (200kHz-700kHz range for these supplies) and the first
few harmonics if I go looking for them, but they're certainly not an
issue at 144MHz. With enough shielding and bypassing (done right), I
suppose any switcher would be clean enough. With a switcher of good
design, you won't even need any additional shielding or bypassing.

Cheers,
Tom

You can tweak up the power on a 24VDC switcher to cover the headroom for a
linear regulator following the switcher. This is an old technique - and
still used. My preference would be an adjustable regulator with the adjust
pin bypassed with 10uF. Linear Technologies has some regulator chips that
out of the box have noise lower than garden variety LM317/337.

You may have to shield the supply --

John Ferrell wrote:
On Mon, 28 Jan 2008 11:27:20 -0000, "Richard"
wrote:

I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding
24V @ about 300mA.

Are switch-mode powers supplies alright or are they too noisy to be used for
receivers? TIA.
Some are, some are not. You have a lot of choices available at 300ma.

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"


I tried one that created all kinds of interference. I was able to
solve the problem by installing caps in parallel with the rectifiers, .
005uF disc I think.


Jimmie

On Jan 28, 10:27 pm, "Richard" wrote:
I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding
24V @ about 300mA.

Are switch-mode powers supplies alright or are they too noisy to be used for
receivers? TIA.

Their noisy period, but you might get away with it on 2m. But you will
still be QRM'ing everyone else...
Hold AM transistor radio next to it, have a listen as you tune across
the band....not nice, lots of spurs with rich harmonic content...

Its your choice. The dark path or the light path of Radio Karma....

Andrew VK3BFA.

On 28 Jan, 11:27, "Richard" wrote:
I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding
24V @ about 300mA.

Are switch-mode powers supplies alright or are they too noisy to be used for
receivers? TIA.

I use a 12V switcher with my FT-817D, it's very quiet.

Leon

On Feb 4, 10:13 pm, Leon wrote:
On 28 Jan, 11:27, "Richard" wrote:

I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding
24V @ about 300mA.

Are switch-mode powers supplies alright or are they too noisy to be used for
receivers? TIA.

I use a 12V switcher with my FT-817D, it's very quiet.

Leon

You were lucky - you got a quiet one. And its the luck of the draw,
unfortunately.

How come we have all been conned into these switchmode things? - by
their very nature, without a lot of effort, they are noise generators.
Their cheap to make, thats their only advantage - everything else is
part of the spin cycle. And if it works on 2m and above, fine - you
will just be adding to the already horrendous RF pollution from
thousands of the bloody things already on HF - the suburbs are getting
unbearable, S9 plus noise, every night, on 80m.....160 aint to crash
hot either...

I refuse to have to work on a power supply to get it quiet enough to
be used with a radio. I am interested in the radio, not fixing
shortcomings in design of things that , by their very nature, are
unsuitable to be used near radios. That sucks. Linear technology is
far easier and quieter...

Andrew VK3BFA.