[hpsdr] Analog Vs. Switching power supply for OZY Janus...

[Tony Langdon]

At 05:50 AM 6/12/2007, k5nwa wrote:

>The problem I see with switchers is that although they could be made
>quiet, many do so at different degrees of success, so buying one is
>somewhat of a gamble unless someone else has had experience with the
>particular model that one is interested in. With an analog supply on
>the other hand, it's a non-issue.

I'd agree switchers can be a gamble.  My experience with cheap 
computer switchers is they are highly variable, from quiet to 
noisy.  On the other hand, the 40A switchmode I use in one of my 
shacks is quiet as a church mouse.  One of the local hams actually 
disassembles his and found at least 5 separate stages of 
filtering.  On HF, there were some birdies that were barely 
detectable with no antenna on the radio.  When the antenna was 
connected, the HF noise floor swamped any noise from the power 
supply.  My experience is identical.

OTOH, the difference in heat dissipated and the light weight of the 
power supply are readily apparent.  The supply powers a small 
repeater, and it's nice to not have to worry about how hot the thing 
is getting.  The previous linear supply used to have a 5" fan aimed 
at its heatsink to ensure proper cooling.

Another subtle thing - a common failure mode of linear supplies is 
for the pass transistor to fail shorted, so you need a good crowbar 
to protect the radios.  Switchmode supplies most commonly fail with 
no output, so if it smokes, the radios have better odds (though like 
everything else, there is always the possibility of linear supplies 
failing dead and switchmode ones putting excessive voltages onto the 
supply rails, as anyone who's had computer parts fried by a wonky 
power supply can attest to.


>Hopefully as people try out different models they will publish their
>results so a list of good switchers can be compiled.

Well, once a good switcher is identified, that's what I intend to go 
with for weight, space and power consumption reasons.  Just have to 
find a suitable one that's as quiet as the big bench 
supply.  Speaking of which, I've seen another 13.8V bench supply 
(switchmode) come onto the market - the other shack is likely to get 
one of those, and the linear supply retired to light duty elsewhere 
in the house. :)

73 de VK3JED
http://vkradio.com


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