[hpsdr] ADC Overload, a conclusion.
Graham / KE9H
KE9H at austin.rr.com
Sat Oct 20 06:21:09 PDT 2012
Jeff:
Some curiosity questions:
When you say a level of -18 to -16 dB's, do you mean dBm or dBFS or ... ?
Preamp on or off when you were having the overload?
What brand and model of power supply? (This is one to watch out for !)
Thanks,
--- Graham / KE9H
==
On 10/18/2012 7:37 AM, Jeff Cook wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Using KISS Konsole (thanks George) as a spectrum analyser I was able
> to see a large peak very much down at the LF end of things. Going over
> to the narrow band view and tuning, I found the peak to be at 0.7033
> MHz with diminishing harmonics at either side. This peak was at some
> -18 to -16 dB's and was static in amplitude and width, therefore not a
> broadcast station but something much closer to home. This ghastly RF
> noise was being generated by my main switch mode power supply which
> supplies 29 amps at 12 V. Switching this off and reverting to my
> linear 25 amp power supply removed the spike, further tuning revealed
> a another series of spikes centred on 0.4525 MHz only half the size
> but nonetheless there. These were being generated by another switch
> mode power supply, a smaller one with 3 different voltage outputs on
> it used to power my Trimble Thunderbolt GPS disciplined clock, the 10
> MHz output of which I use to synchronise Excalibur.
>
> This has completely solved the ADC overload problem I was having on
> receive, however I'm still grappling with a transmit ADC problem.
>
> Thanks to all that helped to point me in the right direction. I'm now
> going to do a carte blanche capacitor replacement in my two switch
> mode power supplies, or, I may just chuck them in the bin.
>
> Jeff Cook, G0AFQ.
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