[hpsdr] ADC Overload, a conclusion.

[Graham / KE9H]

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:
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>
> 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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