[hpsdr] Power supply filtering

[Jeroen Bastemeijer]

Dear All,

Thanks for the link, N0UU. I downloaded the document. Allthough general 
principles still apply, I noticed the AN is quite old (1986!).

Michael Ardai gave a few good suggestions for the supporting electronics 
of Demeter (like the ADC etc.).

Andreas Troschka and Tony Langdon send mails with regard to the EMI of 
switchers. On this point I would like to add the following:

Designing a "quiet" switcher is not as easy as building a "quiet" linear 
supply. However, it is my strong belief that it can be done. By using 
proper grounding, effective filtering and a proper lay-out of the PCB. 
The main advantage of a switcher will be the lower power consumption and 
less heat.
Some other words about EMI: We shouldn't panic too much about the noise 
which is generated in Demeter. The whole HPSDR is filled with all kind 
of sources for EMI (e.g. clock-oscillators and data-busses). One might 
argue that the power in Demeter is higher, but this doesn't mean 
necesseraly that the noise induced in the SDR will be bigger. Some times 
there is a stronger electric coupling (E-field) instead of a magnetic 
coupling. So a small signal clock line close to a sensitive input could 
cause more noise than a "heavy" switcher at couple of inches away....

I'm certainly willing to make some experiments with switchers and see 
how quiet they can get.

Tony wrote: " I would consider a low current linear supply for 
everything except the PA. "

Thsi brings me to the point: How much power do we need? I made an 
assumtion, based on some measurments (from the Jnaus/Ozy combo), but the 
rest of the power consumption is still a mystery....

Next step has to be to mak an inventory of all the "power-hungry" cards 
which will populate the HPSDR. Is this a nice task for Phil? Are you 
willing to do that? Otherwise, I will contact each project-leader myself 
and ask the about real life numbers or good approximations of the power 
needed.

Thank you,  73 Jeroen PE1RGE

stoskopf at tri.net wrote:

>***** High Performance Software Defined Radio Discussion List *****
>
>For a good discussion of output filtering on switcher supplies see:
>
>http://www.linear.com/pc/downloadDocument.do?id=4176
>
>starting at p. 59 of AN19.  Be sure to read the final comments at the end.
> Great sense of humor.
>
>I still haven't figured out the proper source/loads for modeling in say,
>SwitcherCad.
>
>N0UU
>
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-- 
Ing. Jeroen Bastemeijer

Delft University of Technology
Department of Electrical Engineering
Electronic Instrumentation Laboratory
Mekelweg 4, Room 13.090
2628 CD Delft
The Netherlands

Phone: +31.15.27.86542
Fax: +31.15.27.85755
E-mail: J.Bastemeijer at TUDelft.nl
GPS: Lat N52.00002 Lon E4.37157 Alt 46.2m


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