[hpsdr] SMPS the wrong way to go

[Kjell Karlsen]

Hi Francis.

I can assure you that a SMPSU constructed according to the advices given  
by LT in their application reports and using the right components do NOT  
introduce any spurs higher than the noise level in Hermes on any Amateur  
bands (or  outside too). Even the oscillator frequency near 1,8 MHz is  
down to -120dBm. I can not see any spikes higher than 5mV on input or  
output when using an oscilloscope.

I was very skeptical to use SMPSU on the same board as the RX. If you use  
a switching frequency lower than 600KHz it is very difficult to get rid of  
the spurs, but at 1,5-2 MHz using modern ceramic capacitors and ferrite  
beads in addition to shielding and proper grounding there will be no  
problems.

On Hermes Beta the spurs coming from the other clocks on the board are  
much more difficult to get rid of.

73, Kjell



På Tue, 10 Aug 2010 22:14:04 +0200, skrev FRANCIS CARCIA  
<carcia at sbcglobal.net>:

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