[hpsdr] hpsdr] About the Dynamic Range of Receivers

[KA2WEU at aol.com]

About  the Dynamic Range of  Receivers

It has nothing to do with the  instantaneous dynamic range, which is
defining
the radio's capabilty to  discern a weak signal (near the noise floor) in
the
presence of a much  larger signal. The maximum possible  ratio of the two
signal's levels  is called instantaneous dynamic range).
The overall instantaneous dynamic  range of the receiver is not limited by
the nyquist dynamic range of the  16-Bit ADC (about 95 dB).

N1UL:
 

Please  note ADC's quantization noise having a part in the receiver's
overall noise  figure (NF): At the ADC input the thermal noise from the
front end and the  quantization noise will add up. To keep the ADC's part in
overall NF as low  as possible (<1dB), the gain from antenna to ADC should
be set so that  for the front end noise will dominate the quantization noise
from ADC by  about 10 dB. This will further reduce the overall instantaneous
dynamic  range of the receiver !

DSP is decimating the ADC sampling rate from  100 kS/sec down to rates
appropriate to the actual
CW / SSB signal  bandwidths of (50)300 ... 3100(4500) Hz (meaning  Fs=
781.25 / 1.5625  / 3.125 / 6.25 / 12.5 kS/sec)./N1UL
 

Noise  coming from ADC (including the  quantization noise) is reduced  by
just
the ratio of ADC's nyquist bandwidth (=50  kHz) to the  signals bandwidth,
thus
giving a corresponding gain in dynamic  range  of  ...     >
>  _______________________________________________



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