K3 on Order

[John Ragle]

     This topic goes around every few months, and I hesitated
(unsuccessfully) to add to it this time around.

      I have several inexpensive 25-amp switching supplies from Radio
Shack and Pyramid. I also have a couple of "linear" supplies that are
built like the battleships of yore, and some gel batteries for portable
operation.

     I have used these supplies in various combinations on a K2/100, a
K3/100, and an ICOM 910H. I have never been able to tell the difference
in noise level between any of these sources. My two rigs sit ~2 to 3
feet from a computer,and I have occasionally also put a small laptop
directly in front of the XCVRs. Same comment: no discernible noise from
the computers...they are impressively shielded with finger-stock, etc.
Some lines have ferrites on them because that's the way they came from
the factory.

     I do have a few birdies up and down the bands, but these are
apparently from external sources and disappear when I disconnect my
antennas or switch over to my dummy loads. My antennas are fed with good
quality coax, and I live in the boonies. The nearest above-ground
utilities are a city block away. I imagine this is a fairly quiet location.

     When I bought my first K2 I was concerned about this question,
hence the linear supplies. My current take on this question about
switching power supplies is that it is/was a needless worry. I suppose
that if one is using open-wire feeders the situation might be different?

John Ragle -- W1ZI
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[lstavenhagen]

My experience is the opposite - I haven't yet used a switching PSU that _didn't_ cause some kind of nasty noise in my rigs, usually like computer generated noise. A broadband hash with spikes of hum at various places is usually what I get.

I simply threw batteries at the problem - now I exclusively use my 80AH wheelchair battery for my K2 and K3 with no more troubles. The PSU's either went in the trash or were sold, and the money was used to buy my battery....

73,
LS
W5QD

[Douglas Furton]

I'll add my two cents about switching power supplies here as well.  I bought an HPS-1a PS from Gamma Research.  This is a tiny switching power supply not too much larger than a deck of cards, yet it can deliver about 100W voice, and maybe 80W slow CW with my K2.  It is marketed as a "hybrid" PS because it uses a great bit of capacitance to smooth out the duty cycle, all fed by a small, switching PS.  

In a nutshell, this little switching PS works great.  I use it in my home shack sometimes, and when I set up in my backyard (not quite a DXpedition, but fun...) and have not noticed any noise.  On the down side, this particular unit was a bit expensive.

Anyway, I am a new ham, and originally was convinced by what I read that one should avoid switching PSs at all cost.  Perhaps switching PSs are better engineered now than in the past.  When my main supply -- all iron, size and heat -- gives up the ghost, I'm replacing it with a modern, efficient switcher.

Cheers,

Doug
K8EXB

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[Don Cunningham]

In all fairness to the switching supplies, if you are forced to have indoor
antennas or close to the ground "stealth" antennas, you might not want to
consider them.  Of course they will generate noise in those cases.  I have
decent outdoor antennas and still have to be careful with computer switching
supplies and their placement in the shack.  I probably have a lifetime
supply of heavy, Astron linear supplies, but the size and weight of the
Samlex and other supplies is sure getting tempting!!  That RS-50A is getting
AWFULLY heavy to move, hi.
73,
Don, WB5HAK

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[Vic K2VCO]

I think a lot has to do with the antenna, and how it's connected to the rig. If you are
using a balanced antenna, properly fed with coax and a balun or two-wire line with a
well-balanced tuner, it's unlikely that you will have a problem. If you have a wire stuck
in the coax connector of your rig, then you almost certainly will. Other setups will be in
between.

A dipole fed with coax with no balun will certainly be vulnerable to picking up noise on
the outside of the shield. Noise currents flowing on the shield will then be connected
directly to the antenna at the feedpoint! If the coax runs near power wiring which is
connected to a switching supply (or computer, etc.) then you are asking for trouble.

Having said that, I'm sure some switchers are worse than others. But it's very hard to
make one at consumer prices that doesn't allow some noise to escape.

On 7/17/2010 7:13 AM, lstavenhagen wrote:

>
> My experience is the opposite - I haven't yet used a switching PSU that
> _didn't_ cause some kind of nasty noise in my rigs, usually like computer
> generated noise. A broadband hash with spikes of hum at various places is
> usually what I get.
>
> I simply threw batteries at the problem - now I exclusively use my 80AH
> wheelchair battery for my K2 and K3 with no more troubles. The PSU's either
> went in the trash or were sold, and the money was used to buy my battery....
>
> 73,
> LS
> W5QD

--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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[Jim Brown-10]

On Sat, 17 Jul 2010 08:32:24 -0700, Vic K2VCO wrote:

>I think a lot has to do with the antenna, and how it's connected to the rig. If you are
>using a balanced antenna, properly fed with coax and a balun or two-wire line with a
>well-balanced tuner, it's unlikely that you will have a problem. If you have a wire stuck
>in the coax connector of your rig, then you almost certainly will. Other setups will be in
>between.

>A dipole fed with coax with no balun will certainly be vulnerable to picking up noise on
>the outside of the shield. Noise currents flowing on the shield will then be connected
>directly to the antenna at the feedpoint! If the coax runs near power wiring which is
>connected to a switching supply (or computer, etc.) then you are asking for trouble.

Exactly right. What matters is not proximity of the power supply to the rig, but the power
supply to the antennas!  

I have some switchers in my shack and in my house. Most of my antennas are high and away from
those noise sources, but two antennas (160M and 2M) are quite close to the shack. I have
ferrite common mode chokes on ALL of those switchers, and I had to get VERY serious with the
two cheap switchers in my shack that float-charge my batteries to kill the noise on 160M and
2M. They're now quiet, but they didn't come that way. :)

73, Jim K9YC



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[John Ragle]

On 7/17/2010 11:10 AM, Douglas Furton wrote: (JLR edited)
> ...Perhaps switching PSs are better engineered now than in the past...
=====

I can tell the assembled multitude that this assessment is correct.
Before retirement, I did a lot of weak-signal work in the lab (related
to NMR imaging), and in the earliest days of this work, ca. 1970 or so,
I used Apple-2-Plus machines for data collection. Some of you may recall
that these small microcomputers were powered by open-board switching
power supplies, and the cabinets contained no shielding whatsoever. They
were exceedingly potent sources of RFI and had to be kept "isolated"
from the spectrometer circuitry. At some point, I considered "isolating"
them by taking them out in a field and burying them. Fortunately,
technology advances.

My comments about proximity were to the point that modern devices
(computers or switching power supplies) are very well shielded, as are
modern XCVRs. The Radio Shack 25 amp switchers that I have contain good
shielding AND massive ferrites on the inside of the cabinet directly on
the DC terminals. The AC line cord is similarly ferrite-trapped,
directly inside the metal cabinet. The computers (a la FCC
type-acceptance regulations) have RF-tight enclosures with close-fitting
fingerstock around the openable places and below-cutoff screening on the
fan ports. My K2 and K3 are exceedingly well shielded...surely an open
100-watt source a couple of feet from a computer would make itself known.

I think it is really a question of "physician, heal thyself" -- I
believe that some truly have the problems they report, and that they
have taken the correct steps to ameliorate them. But...my overall
opinion is that switching power supplies have taken a bad rap. My linear
supplies are gathering dust, keeping their shelving from floating up
into the air. Maybe the way to convince oneself one way or the other is
to buy an inexpensive Astron or Radio Shack supply and try it.
Also...with care...batteries make very good "filters."

John Ragle -- W1ZI





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[Jim Brown-10]

On Sat, 17 Jul 2010 12:47:44 -0400, John Ragle wrote:

>But...my overall
>opinion is that switching power supplies have taken a bad rap.

There are switching power supplies and there are switching power
supplies. Not all are created equal. If you go to an electrical
supply store to buy a transformer to run 12V lighting, they will
sell you a switching power supply that is a holy terror. They call
it an electronic transformer. Ask them for a real transformer and
you get a blank stare.

Most wall warts that provide DC power for battery charging, or to
run consumer electronics of all sorts are switching power supplies.
Many of them are quite noisy.

73, Jim Brown K9YC



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[Vic K2VCO]

Two Field Days ago I brought along a little clip-on lamp. It was small, bright and very
convenient. Its 12v bulb was powered by a tiny switching supply.

It was only turned on for about a minute. Now I call it the Hissing Lamp from Hell. I
don't know if it also generates the usual unstable noise vortices that roll around the
bands, but it does produce a loud wideband hiss that sounds like nothing as much as the
noise generator that I use to adjust my K2's filters. In fact, I could use it for that
purpose.

Cheap switching supplies: really bad technology whose time has come!

On 7/19/2010 8:15 AM, Jim Brown wrote:

> On Sat, 17 Jul 2010 12:47:44 -0400, John Ragle wrote:
>
>> But...my overall
>> opinion is that switching power supplies have taken a bad rap.
>
> There are switching power supplies and there are switching power
> supplies. Not all are created equal. If you go to an electrical
> supply store to buy a transformer to run 12V lighting, they will
> sell you a switching power supply that is a holy terror. They call
> it an electronic transformer. Ask them for a real transformer and
> you get a blank stare.
>
> Most wall warts that provide DC power for battery charging, or to
> run consumer electronics of all sorts are switching power supplies.
> Many of them are quite noisy.
>
> 73, Jim Brown K9YC

--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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