[hpsdr] About the Dynamic Range of Receivers

[Greg Overkamp]

I have a question regarding this explanation of
instantaneous dynamic range. After decimation, the
instantaneous dynamic range is measured only over the
bandwidth of the output of the decimation filter. What
if the weak signal is within the passband of the
decimation filter, while the strong interfering signal
is in the stopband of the decimation filter, but below
fs/2 of the A/D converter. Can the dynamic range still
be considered to be improved by decimation? In this
example, can the dynamic range still only be measured
over the bandwidth of the output of the decimation
filter? If this same strong signal necessitates a
reduction in gain ahead of the A/D in order to keep
the A/D from saturating, can the instantaneous dynamic
range still be considered to be increased by the
decimation process and only measured over the BW of
the decimation filter passband?

This has been bugging me for awhile. Any help on
clearing this up is appreciated.

Greg Overkamp
WD9DEX



 
> 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). DSP  is decimating 
> the ADC sampling rate from 100 kS/sec down to rates
> appropriate to  the actual 
> CW / SSB signal bandwidths of 300 / 3000 Hz (meaning
>  Fs= 781 / 12.5 kS/sec). 
> 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