On Nov 2, 2008, at 8:16 PM, Sean Breheny wrote:

> As a hobby project I have slowly been building a high-performance HF
> receiver over the last few years. I originally used a switching power
> supply in it. Granted, I'm only slightly beyond newbie when it comes
> to switching power supplies, but I have to say that I found it
> impossible to keep the harmonics from the switcher from making it into
> the receiver. I tried shielding and massive filtering on the input and
> output leads to no real avail. I did not try magnetic shielding,
> however the physical separation between the switcher and the rest of
> the receiver was such that I would find it hard to believe that there
> could be direct magnetic coupling.

Some of the modern "radio grade" switchers provide user controls to  
move the harmonics around by modifying the switcher's frequency, etc.

If you're stuck with a switcher, you might try that.  You could also  
do some reverse-engineering on the Alinco switcher that started the  
trend toward having that type of control back about 10 years ago:

http://www.eham.net/reviews/detail/765

It still gets good reviews, and I know a number of hams using them.

> I'm sure that it is possible to use switchers in receivers but I think
> that lots of effort would be required. I am not surprised if switchers
> are rare in receivers.

Depends on how wide the receiver front-end is, and what you're trying  
to hear.  :-)  I've seen lots of switchers that had fixed frequency  
noise outside of the bands desired for reception.

--
Nate Duehr
nate@natetech.com



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