> 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 _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
