[hpsdr] Go linear!

[Ken Klein]

After trying out several ATX power supplies that generated way more noise
into the SDR/J/O system than I could tolerate, I decided to go the linear
route.  I bought an old Radio Shack 13.8-volt 2.5 amp power supply on Ebay
for 10 bucks.  I also bought an LM7805 regulator (Mouser 512-LM7805ECT) to
give me +5 volts, and an L7912 (Mouser 511-L7912CV) for the +12 volts.   For
the -12 volts, I bought an 18 volt 130 ma transformer (Mouser #838-3FD-336),
an L78S12 regulator (Mouser 511-L78S12CV), and a bridge rectifier (Mouser
821-DB102G), and found a handful of junkbox capacitors.  Total cost outlay
for everything including shipping is less than $35 bucks, and it all fits
into the original Radio Shack chassis with its integral power cord, fuse,
and circuit breaker.  I have ample power to power the Janus/Ozy as well as
the 1W SDR, and probably enough power left over for the future projects.
I'm considering buying two 15-volt regulators to add to the soup in order to
get rid of the +/- 15 volt switcher on the SDR.  And it's QUIET!  No need to
go to all the trouble to filter out switcher spikes (or adjust switcher
frequency to get it off the passband).  Most shacks already have a big
linear 13.8 supply; the rest is pretty trivial.

 

So I vote linear.  IMHO, it's cheap, dirt simple, and quiet.  A little
heavier, maybe, and perhaps a tiny bit bulkier, but it's much cheaper and
cleaner.   Remember that we are in an environment where quiet is paramount.

 

Someone earlier asked about design of all this.  Just look up the spec sheet
on any of the regulators for the circuit.

 

My two cents.  Thanks.

 

Ken WR5H     

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