> if no signal was converted during the A to D stage, there will be no
> signal to "dig out" during the D to A stage.
The A/D conversion sensitivity is easy to calculate, more bits mean more
sensitivity, more samples more definition, more sample rate more definition.
The issue is before and after the A/D. Most new radios are using SMD
inductors that saturate with RF energy outside the band. High IP3 radios,
real IP3 use large inductors, 1/2" diameter can barely hold 30 db IP3, SMD
inductors saturate with RF energy and generate reciprocal noise and
intermodulation's. A good filter on topband is a must before a good
preamplifier.
The issue after the A/D is the software filter, making it easy; to get sharp
edges, the signal goes several times though the same filter, this number is
called TAP, increasing the numbers off Taps, you have a sharp filter, but
more phase noise. That phase noise covers a weak signal. Here the more you
make the filter sharp; more you cover the weak signal. Most SDR filters are
designed for deep and clean filters, not for weak signals. It is a hard work
and needs a genius to figure it out. Example. Doug NX4D reduced the numbers
if TAP on his Ten Tec Orion to be able to copy weak signals, the filter
becomes wide and round shape. It is complicated to adjust for good shape and
low phase noise.
I am not a software guy; my experience was based on analog signals
amplifiers and transducer for instrumentation; before A/D's.
73's
JC
N4IS
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