Are switch-mode powers supplies suitable for receivers?
Richard
24V @ about 300mA.
Are switch-mode powers supplies alright or are they too noisy to be used for
receivers? TIA.
Mike Andrews
Richard <nearlyne...@ntlworld.com> wrote in
<605sh6F...@mid.individual.net>:
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 Bastard, in rec.org.sca
Allodoxaphobia
> 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:
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>
John Ferrell
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"
K7ITM
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
jack
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 --
jimm...@gmail.com
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
Andrew VK3BFA
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.
Leon
I use a 12V switcher with my FT-817D, it's very quiet.
Leon
Andrew VK3BFA
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.
K7ITM
There's another advantage of a switching supply that is very important
to some of us: efficiency. The receiver I've been working on runs
from 5VDC, but I have to supply power at 1.0V, 1.2V 1.8V, 2.5V and
3.3V, and each one of those uses a switcher. A linear regulator to 1V
from 5V will result in a supply that's 20% efficient. The switcher
I'm using for that supply is about 87% efficient under its operating
conditions. If I tried to run all my supplies with linear regulators,
I'd have to supply over twice the power; it would come close to
violating the power rating of the 5V supply, and power dissipation in
the receiver would result in excessive heat rise.
But even with all those switchers, the only spurs greater than about
-145dBm (antenna-input-referred) and greater than 1.5MHz are from
digital circuits, not the power supplies. -145dBm is, I believe, 20dB
_below_ S1 by usual definition of the S-meter units. Even the power
supply fundamentals are only at about S1. And the supplies are not
themselves shielded. (The receiver RF circuitry is, of course, as is
the whole receiver module.)
I would be much more circumspect about using a switching supply in a
homebrew receiver that was going to be used where power dissipation
wasn't an issue, but then I'd do a lot of things differently than I
have for such a receiver. It wouldn't keep me from using switchers;
I'd just look at the whole design in a different way. On the other
hand, finding ones that would be adequately quiet for a 144MHz
receiver should not be difficult at all.
Cheers,
Tom
Andrew VK3BFA
Hi Tom,
all points noted, and readily conceded - if the things didn't have
SOME advantages besides low cost, well....
You've got yours down to S1 - mm, well,......so thats the noise floor
you are limited to. And thats probably on a small range of
frequencies, gawd knows where else it is radiating...(and adding to
phase noise in your receiver...)
And, lets be honest, if it isn't causing ME QRM, on the frequency I
want to operate, then its OK......fine for VHF/UHF unless a spur is on
your IF frequency...
The only application I can see for them is, as you say, where low
power consumption/efficiency is paramount - but if you can plug your
switch mode power supply into a source of AC power, then whats the
problem with lugging a quiet linear supply as well as the generator
required to run it?
To me, they are a flawed technology, and in a better place would not
be allowed to be used because of their inherent design flaws...
Andrew VK3BFA.
(PS - I do a good "back in the good old days" rant if you like.....)
Bryan
> On Feb 5, 3:52 am, K7ITM wrote:
> > On Feb 4, 3:55 am, Andrew VK3BFA wrote:
> >
> >
> >
> > > On Feb 4, 10:13 pm, Leon wrote:
We use a couple of homebrew regulated DC-DC boost converters during Field
Day, one to run the HF xcvr (13.8VDC @ 25A peak) and one to run the laptop
PC for logging (16VDC @ 4.5A), from a 12V wet cell battery "pack"*. Prior
to use, they were "sniffed" (at no load and also full load) with an HP
spectrum analyzer. The analyzer showed only a few very weak spurs in the HF
spectrum that we couldn't hear at all, even on 80m. Of course, they were
properly designed with this use in mind... good decoupling and shielding.
Switching rate is 500KHz; efficiency is in the neighborhood of 90%.
* Battery "pack":
http://img22.imagevenue.com/img.php?image=65659_battery_pack_122_1054lo.jpg
Bryan WA7PRC
K7ITM
Oh, well, the receiver is 100kHz (nom.; actually is -3dB at about
18kHz) to about 38MHz. It also alternately does 70MHz IF at 36MHz
bandwidth, at about the same sensitivity. Noise figure on HF is
around 9dB at max sensitivity; since switchers are not stable sources,
their output becomes broadband noise by the time you get to bandwidths
low enough to see -145dBm (e.g., 100Hz), and there's essentially no
indication of increased noise floor at the harmonics (past maybe the
third) of any of the supplies, even with lots of averaging. The
master clock is a low phase noise VCTCXO, and it IS run from a linear
supply, with scrubbing added. That oscillator really does set the
system phase noise. There are no other oscillators to worry about in
the signal chain.
You're welcome to rant about the "good old days," but I probably won't
hear it. I'm too busy enjoying the "even better new days" to bother
looking back.
Cheers,
Tom
Andrew VK3BFA
Hey - I agree - I like the modern DDS chips as well, fantastic things.
(Note - AD specify separate ANALOG supply for them...Mmm?)
I try again - my point is, why bother to stuff around getting a "new"
technology to work when an "old" technology is cheap, easy,simple, and
it works with no extra fiddling.
And if you need a spectrum analyser to check your power supply for
suitability, - that is a bit ludicrous, isn't it? Mad Scientist in
attic room / Tony Hancock sketch sort of thing. Why make things so
difficult? KISS.
Never said there were no quiet switchers - just that the majority were
not....Google on SMPS noise to prove.....
Andrew VK3BFA.
Ian White GM3SEK
>
>Never said there were no quiet switchers - just that the majority were
>not....Google on SMPS noise to prove.....
>
(as you claimed a few days ago).
It's all about skill and care in the design - above all, the input and
output filtering. Done correctly, there are no problems, as proved by
the many base-station HF transceivers that have a mains SMPS built in.
When you buy a separate SMPS, don't trust to luck. Be an intelligent
consumer: read the reviews, specify what you need, ask what has been
done to minimize the noise levels, and be prepared to return the unit or
walk away.
The only real "luck" is about the SMPSes in other things that your
family and neighbours may buy...
--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
Andrew VK3BFA
MM, well.....ok., I will add a rider to the "luck of the draw" - if
you have the knowledge of the things in the first place, it is
axiomatic that you would need to check it out before you buy it - get
test data, spectrum analyser screen shots, copy of CE certification'
load test data, a copy of the service manual for future
reference...probably a few more things as well, I forget.
The rest of us, well.........we basically know bugger all about them,
and we havent been hams long enough for someone to tell us "Brand X"
is useless. SO we go and buy it, and wonder what the hell went wrong.
And I been fixing the things for 20 years now as a lowly service tech
- horrible things, havent seen a quiet one yet..
AND AND...its going to get worse. Plasma TV's radiate to buggery -
they have big, and good, filters on the SMPS power supply, but they
are S9 at 5 miles.......LCD is better - EXCEPT for the plug pack SMPS
type 12v etc power supply hanging off them...had one in for repair,
the only sign it was polluting was that the (non ham) owner complained
it was interfering with his AM radio reception. (That was interesting
in its own right - he had contacted the relevant authority, they had
sent him a "do it yourself" booklet, and he found it...I thought that
was a pretty good effort)
And the "Brand X" (still on sale, still selling in the shops) - one
hapless inexperienced amateur asked me to "modify" - ie quieten it
down. Plastic from and rear panels. Bugger all input filtering - and
virtually none anywhere else. On 160m, spot frequencies, it was S9+. I
got it down to S3, then gave up in disgust.
So, Ian - love your columns, in awe of your knowledge about practical,
real radio. I certainly havent got all that much. But this is the
view from the trenches, as it were - everyday practical pointy end
servicing - so,if I may, I humbly beg to differ. No offense meant, to
anyone, and none taken. (Yep - its true - I don't like them...)
Andrew VK3BFA
Highland Ham
When using a switcher (in a metal sealed enclosure and with noise
supressors ,as recommended by some in this thread), put a sealed lead
acid battery in parallel.
If still noisy you then can switch-off switcher when rx-ing .
Frank GM0CSZ / KN6WH
Joel Koltner
>> 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.
Other advantages include much better power efficiency and much lower weight.
It's not particularly difficult to make a switcher with very good (meaning
very little) noise output, but relatively few applications call for it, and
given how incredibly competitive the power supply arena is, it's not
surprising that a lot of companies drop a few components to reduce their costs
at the expense of noise.
Andrew VK3BFA
wrote:
re power and weight - I was having a rant, so deliberately left out
the inconvenient facts.....(Yes, I thats unusual, isnt it - I must
reprimand myself)
And yes, will readily concede the " they can be well designed bit"...
But they are not. The percentage? - dont know. All I can do is hear
them, on air. Went away at Xmas, remote caravan park, MILES away,
looking forward to HF radio . Nope, surrounded by modern caravans with
12v systems, run from noisy SMPS power supplies/battery chargers....it
was better, 80m QRM was S3 instead of S9+
Gosh, modern electronics IS wonderful, isnt it....
My point stands.
Andrew VK3BFA.
numeric
"Richard" <nearlyne...@ntlworld.com> wrote in message
news:605sh6F...@mid.individual.net...
Many years ago I designed a switching power supply for aircraft Nav and Com
VHF radios. The switcher was 100% shielded and line filtered to get the
radio to pass FCC and FAA TSO certification. Even though the Com and Nav
radio's are VHF, they were placed next to an ADF radio (low frequency)
without problems. Testing was performed not only for electro magnetic
emissions, but also for line current emissions, with a line stabilization
network, into the radio from the aircraft power. Even if the switcher is
100% shielded, this will not prevent radiation along the input power line.
You need to consider methods to eliminate pulsed current along the input
power line caused by the switcher. This may be hard to achieve, especially
for high efficiency switchers. A good choke will help, but it will also
introduce additional switching losses. So yes, a switcher can be used; but,
IMHO it must be designed for use in an RF environment.