Question about HDSDR and rsp1 dbfs numbers

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Wizard6733
Posts: 33
Joined: Thu Feb 02, 2017 7:36 am

Question about HDSDR and rsp1 dbfs numbers

Postby Wizard6733 » Mon Nov 13, 2017 12:41 am

While using hdsdr for NOAA satellite reception...I wondered what the numbers meant in the tuning window of hdsdr. The numbers usually flip between a green RF-15 to RF-19 and sometimes it goes to RF<-20...is this good?? When I move the if gain control slider down in the extio...the green numbers increase to RF<-30 or more. I've also seen it red and say !!!clip!!! I'm just not sure what it means and what's good or not

Thanks
Joe

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g1hbe
Posts: 228
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: Question about HDSDR and rsp1 dbfs numbers

Postby g1hbe » Mon Nov 13, 2017 10:20 am

I haven't used HDSDR for ages so I can't help with those numbers, but the CLIP warning means you've got too much gain in the system and the ADC is hitting the stops.

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Andy

DanubeBCL
Posts: 179
Joined: Sat Jul 02, 2016 12:39 pm

Re: Question about HDSDR and rsp1 dbfs numbers

Postby DanubeBCL » Mon Nov 13, 2017 12:13 pm

https://en.wikipedia.org/wiki/DBFS
In short: When a signal is 0 dB FS the ADC converter only creates logical "1"s and cannot discriminate the spectrum signals any more. It overloads. The db FS value indicates how "far" a signal is away from the highest possible value the ADC can handle. It is not a measurement of the quality of the reception. It indicates how much "room" is left before the ADC full scale (overload) is reached. I think a good advice is to keep it below appr. -20 dB FS. The automatic tuner AGC does this for you.
Has also been addressed here:
viewtopic.php?t=389#p1482
73, Heinrich

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