Topband: Desktop power supplies

[Ralph Matheny K8RYU]

It is my opinion that there are two kinds of switching power
supplies---the kind that are messing up your radio today and 
the ones that will at a later time.  I believe they are not
compatible with HF radio at a fundamental level, thought we
must learn to live with them.

Two instances...one noise related, the other not.  A few years
back I setup a packet node at a remote BC location, and was 
blessed with a high quality switching supply.  Every time the 
radio was keyed, the supply would sense the load increase as
a short and briefly pulse the DC output.  This reset the packet
controller, which created several trips to the site before I 
scoped the DC and figgered  out what was going on.  In the second
instance, this past field day somebody managed to get a switcher 
hooked up to our 6M radio without my knowledge.  When the radio 
was keyed, the noise from the normally quiet supply clobbered 
the adjacent SSB station.  Reason:  The supply did not like the
square wave from our generator (rather than the utility sine wave)
and the switcher would "panic" when the load was high. Problem
not apparent on the 6M or HF radio while 6M was receiving...only
a couple amps load.

Never would have thought of those problems.  Switching power 
supplies are very sneaky as well as potentially noisy.  They 
work well with steady loads under ideal conditions.  They work 
well when new when all the line-filter caps are in tact, but the
quality of those little caps isn't always the best and they get
popped at the worst time. 

Switchers are a fact of life....but any time you can avoid one 
on your operating table, I say do it.  Same is true of the little
curley-Q lightbulbs (with a switcher inside)...

One man's opinion....


de K8RYU