sensitivity & selectivity in SDR's
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sensitivity & selectivity in SDR's Expand / Collapse
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Posted Monday, June 7, 2010 6:01 PM
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I am new to SDR's.

What I do not understand is how can you control or make better the sensitivity and selectivity of an SDR ?

Would not sensitivity all be done outside the software/PC with regular RF amplifiers ,tuned stages ,etc ?

How do you control the selectivity of an SDR ?

I could maybe see selectivity being done by software ( this is done at audio ,correct ) but how can you improve on it ,with new software or a new PC ,how far can you go ?
Will you not eventually only be able to make an SDR so much selective and that's it ?

Looking forward to all responses,

Al ( al2 )
Post #2779
Posted Tuesday, June 8, 2010 1:02 PM
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Al,
Sensitivity of an SDR radio are determined at the input to the ADC... In the case of the Flex series of SDR's ( see exception below) with the internal preamp on, there is more than enough sensitivity on the HF bands such that the your demodulated signal to noise ratio is determined by your antenna effecency and ambient noise level. Adding more gain by preamps will NOT improve your recovered signal to noise ratio and may actually make it worse. ( exception: The Flex 5000 suffers a bit on 6 meters and can benefit from a low noise figure external preamp in low ambient noise level locales. The Flex 3000 has a low NF preamp built in.)
As for adjacent channel selectivity, that is accomplished in software.. PowerSDR with a Flex radio has better selectivity than you can get in any non-SDR radio. Probably more than I will ever need.. But if more is required, its just a matter of having enough computer horse power and a friendly DSP programmer.


AL, K0VM
SDR-1000, Flex5000, Flex user since 2006
Post #2780
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