[time-nuts] Thunderbolt Supply

[Larry McDavid]

I think you should look at the specifications for the noise-rejection 
capability of those three-terminal regulators. They are simple and 
inexpensive but not particularly good at noise rejection. Some of the 
noise from the switcher supply will pass through. Is it enough to cause 
a real problem? Unknown to me as yet.

The power requirements of the Thunderbolt are not the usual ones you see 
standard supplies designed to meet. I have yet to find a small linear 
supply that is adequate that does not absolutely dwarf the Thunderbolt 
itself!

Back in The Day, one could find a good assortment of multiple-secondary 
power transformers that would allow us to build a simple linear supply 
with the three-terminal regulators; there would no switcher to generate 
noise. Alas, these transformers are no longer easily available today. I 
think it can be done with two separate transformers but with the 
filters, regulators and actual wiring, this adds up to a lot of work!

TAPR does offer a 13 vdc input, three-output power supply kit for their 
software-defined radio kits, but its -12 vdc output comes from a 
switching dc-dc inverter. That -12 vdc does supply the Thunderbolt OCXO 
so I have some concern about noise on that power feed.

One could get a custom-designed PC board mount transformer and develop a 
board to supply adequate power. I doubt there is enough interest or 
purchase volume to justify this, however.

So, I'm still looking for a compact linear power supply. I welcome your 
suggestions!

Larry W6FUB


On 2/14/2011 10:06 AM, EWKehren at aol.com wrote:
> Yes I am doing it with some very low cost switchers off ebay, followed by
> linear regulators as I mentioned previously. Works great.
> Bert Kehren
...

-- 
Best wishes,

Larry McDavid W6FUB
Anaheim, CA  (20 miles southeast of Los Angeles, near Disneyland)