[TenTec] Station power supply??

[Bob McGraw - K4TAX]

Not only is the fan quiet there is NO RF NOISE of concern from the Astron 
SS-30M.  There are a few birdies that I found, but these are not in any ham 
band or even close and with an antenna connected, they are buried in the 
noise.  I've looked at the output on the spectrum analyzer just to make 
sure.   I also used a bias T with the radio on a battery and the supply 
feeding rated current and tuned the ham bands.  No power supply noise found. 
This is on a current model Astron SS-30M.

There are a few things to look for or check:
** Make sure the 3rd pin is connected to the chassis. Scrape the paint away 
on the inside as necessary.
** Make sure the DC minus is connected to the chassis, same point.
** Make sure the top cover of the supply and the bottom pan are connected. 
I found it necessary to put an internal tooth lock washer between the top 
cover and the lip of the bottom pan just to make sure.  In in doubt, sand 
away some of the paint on both pieces around the screw holes.

Early linear Astron supplies did not have the negative connected to chassis 
internally.  This was originally intended to use in pairs to produce a 
bipolar supply for audio system use.  And these were noted the OVP circuit 
would fault into over current the result of a nearby lightning strike or 
spike on the power line.  The article on "repeater builder" is very clear 
and informative on this point.  Read it and believe it.  (someone else 
posted the link on this topic)

Now here is a switching supply of concern with regard to RF noise.   It is 
3200 VDC @ 1 amp......that is the switcher I use on my VHF and UHF amp.  It 
is about the size of a shoebox and can easily be carried in one hand. It 
does have a pair of hefty fans that do talk to each other as the tip speed 
is not exactly the same.  However the blower on the amp make more noise. 
The good news, there is no RFI coming out on the AC line, on the DC line or 
radiated.  When the HV bypass cap in the amp failed the PS simply shut down 
with absolutely no damage or component failure.  Once the fault was 
corrected. the power supply resumed its normal function.  The bad news is 
that it cost about $0.50 per volt.

I still believe that switching supplies have a valid place in the ham 
station.  Be advised that not all switchers are created equal.  Some are 
indeed noted to produce some RF noise.  Just be sure and select one that is 
designed for HF station operation and not some cheap imitation or knock-off 
or hamfest flea market bargain designed for some other application.  Good 
ones will operate over an input range of 85 VAC to 250 VAC with no range 
selection making them ideal for conditions of varying line voltage.  Their 
output regulation is excellent from no load to rated load.  And good ones 
will have a thermostatically controlled fan and ideally a stepped speed fan 
that increases cooling as needed.

73
Bob, K4TAX


----- Original Message ----- 
From: "Donnie" <cfzepp at gmail.com>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Tuesday, September 04, 2012 7:47 AM
Subject: Re: [TenTec] Station power supply??


>I recently purchased a new Astron SS-30M switcher and the fan is extremely
> quite, unlike a SS-30M I purchased new about 10~12 years ago.
>
> Donnie / WA9TGT
> On Sep 4, 2012 8:42 AM, "Chuck N4XS" <chuck at n4xs.com> wrote:
>
>> There seem to be pros and cons to every power supply choice. The linear
>> supplies are not very efficient, and use a lot of power just idling,
>> particularly the big ones. Switching supplies are more efficient but can
>> add
>> RF noise. I generally get along fine with switchers, but the most 
>> annoying
>> noise for me is fan noise. I bought an MFJ 75-amp supply with lots of 
>> nice
>> features but the fan is much too loud and runs all the time. I considered
>> relocating it to the other side of the wall or building a soundproof
>> enclosure so I wouldn't have to listen to it. Someday I may look for a
>> quieter replacement fan. I have an Icom switcher with a quieter fan, but 
>> it
>> cycles on and off, and even though I am half deaf, it still bothers me.
>> Right now I am using an Alinco DM-330 which is pretty quiet and 
>> efficient.
>> I
>> don't notice any bothersome RF noise from it, but I do have lots of 
>> toroids
>> on my AC power lines, DC station wiring, and antenna cables.
>>
>>
>>
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