I am new to this discussion group, so I may comment about items that
have been covered before, please bear with me.
I am currently finishing an home build SDR receiver front end
project (very much) based on Gerald Youngblood's design published
back in 2003. It is based on an AD9854 IQ local oscillator and a QSD
plus a pair of amplifiers, the whole being preceded by a set of HF
filters.
I have written a little application in VB6 in order to control the
DDS frequency and the HF filter bank using the parallel port.
Nothing fancy, just to run some tests.
Currently I use the following set-up: the audio output of the SDR is
connected to an SB Audigy SE sound card of my desktop PC (the laptop
has no stereo audio inputs) which is running SDRadio (version 0.99),
while the control part is connected to the parallel port of my
laptop PC (the desktop having no free parallel port). It is bit
awkward, but it OK for testing, I'll buy a LPT/PCI card for the
desktop one of these days.
SDradio works great, it is a really remarkable piece of programming,
good demodulation in AM and SSB (I did not try NBFM yet). The low
frequency noise, some 3kHz both sides of the 0Hz is very well
visible (and audible), but can be avoided altogether by tuning
SDRadio some 5...10kHz up or down.
I have a problem though, for some reason I can not fully calibrate
the skew of the SB Audigy board, both the phase and amplitude
cursors should actually be set to some position outside their range.
I did the same exercise with an old SB PCI128 board, this one can be
calibrated all right within the range of the cursors.
I prefer however to use the SB Audigy board, as it has the full 96dB
dynamic range when used at 16 bit resolution, which is some 10dB
more than the SB PCI128 board.
Another thing that would be nice, is the possibility to set the
centre frequency of the spectrum display of SDRadio by an external
program, the little application in VB6 in my case. So that it would
be possible to actually change the frequency including the spectrum
display in one single GUI action. Maybe having some API on SDRadio
or possbly a global variable that would be read by SDRadio.
As I use to listen in on the digtal modes (RTTY, HF fax, ...) I use
other programs such as Hamscope connected to the output of SDRadio.
This is done by actually patching the analog signal from the line
out of one sound board (the one with SDRadio) to the line in of the
other sound board (the one with Hamscope). It would be nice if
SDRadio would have some means to perform this on the internal
digital signal, avoiding a DA and AD conversion.
Thanks for any help or advise and all the best,
Jean.
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