On 30 March 2012 06:38, Johan H. Bodin <[email protected]> wrote:

Hi Wolf, LF

how much dynamic range is needed in a dreamer's band receiver?
The typical 9kHz signals are very small compared to the noise level so there is
plenty of "natural dither". Do you think that a 8, 10 or 12-bit ADC followed by
decimation in SL would be good enough for mHz/uHz FFT resolution? Will strong
sferics be a problem or will some hard clipping be helpful as a "Jimi Hendrx
mode" impulse blanker if the input BW is selected with care?  Maybe quantization
noise would become a problem with such low resolution?

I am thinking about a front end using something like your old I/Q sampling PIC
with a preamp and a BPF. Fs should be close to 4*9=36kHz for near-DC IF but not
too close in order to avoid 1/f noise from the preamp. If the sampling MCU is
clocked with a precision frequency and connected to a simple serial port, we
could say goodbye to soundcard jitter and jumps and other unexplainable
phenomena! Not a "soundCard" really, but a "dreamCard"...

73
Johan SM6LKM

----

[...]
> "slightly different" sampling rate for the ADC and the DAC,
[...]
> soundcard in a laptop makes
> a step change (!) when windows plays a sound through it
[...]
> different SR which is not an integer multiple (or fraction) of the sampling rate
> configured in spectrum lab.
[...]
> the carrier suddenly jumped up
[...]
> might be due to some glitch