[hpsdr] Demeter: PSU's

[Andreas Troschka]

Let me spend my 50Cents on this topic too.
>From the reading of the various posts showing pros and cons of linear and switching power supply technologies I could notice that one important point has been disregarded, EMI.

At the contrary of linear power supply solutions, switching circuits are kings on generating spurs and heavy wideband noise signals.
This attitude is to be conducted to their typical working way, abrupt switching full tensions with very short rise and decay times on each pulse.
This behaviour causes strong RF harmonics generation. Efficiently shielding of such a circuit is far from being such simple as it may seem.

So far a switching power supply is used for computers this is really not worth the attention but this can't be really said if we intend to use it for radio RTX purposes.
We are attempting to extract signals at levels near fractions of microvolts in the HPDSR system. Every dB is important in this attempt or we can delete the "HP" letters from the acronym of this radio project.
We really do not need to increment the overall noise with artificially generated wideband signals coming from the switching power supply.

This kind of disturbs are able to spread themself trough different media as air and the same conductors of the PCBs! Earthing connections, metal shields (as good as they may be), chokes etc., mostly can't  solve the problem.
It is a very tricky exercise to try to stop them and there is mostly no way to avoid them to finally find their routes to reach the sensible frontend circuits and low signal RF amplifiers.

Yes, there are ways to have them cut-off but they require very much effords and experience to efficiently get rid of this signals.

>From a logical point of view it isn't reasonable to voluntary apply a known source of RF noise and then to attempt to eliminate its products from the system when there is an alternative, well tested, simple to realise, cost effective and of sure and repeatable results: the linear power supply architecture.

I'm not sustaining the idea it is impossible to use some switching circuits in the power supply without getting significant noise increase. It is my conviction it's not worth the effort.

vy 73s de IK2WQI - Andreas Troschka




Henry Vredegoor wrote:
> ***** High Performance Software Defined Radio Discussion List *****
> 
> 
> 
> ------------------------------------------------------------------------
> 
> Document that sums up some differences between SMPS's and Linear PSU's
> in I think a nice way..
>  
> http://www.nemic.co.il/Doc/NewsDec03/linear_versus_switching.pdf
>  
>  
> 73's,
>  
> Henry.
> 
> 
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