little tests this weekend.
The sideband suppression, or rather the fact I can't calibrate the
sound card for better than -25dB sideband suppression, is most
probably related to the SB Audigy board, as it is not present on my
old SB PCI128.
With a generator I injected a -60dBm signal at 2000kHz in the
antenna input, the local oscillator was set at 1990kHz, this
produced a line at 10kHz and one at +10kHz on the spectrum
display.
Sampling at 48ks/s, with no adjustments ("reset" on the calibration
window) both signals were showing -58dB and -56dB respectively on
the display. With the best possible adjustment (the "gain" cursor
entirely upward and the "phase" cursor entirely to the right), gave -
80dB and -54dB respectively, or some 26dB suppression.
To my surprise the results are absolutely identical when sampling at
96ks/s.
Out of curiosity, I repeated the same tests with Rocky 1.5 (no
offence, I still like SDRadio more). Setting "shift right channel
by -1 sample" yields a sideband suppression of almost -70dB,
sampling at 48ks/s. The automatic phase adjustment screen indicates
a phase delta of 3° and a gain adjust of 1.06 Sampling at 96ks/s
did not work at all, for some reason the PC did frieze and had to be
rebooted.
The SB Audigy-SE is a good sound card as it features 96ks/s, 24bit
and has an excellent dynamic range (almost 100dB), it is moreover
quite affordable. So it is maybe a good idea to implement the "shift
right channel by " feature as well in SDRadio.
My design (or rather Gerald Youngblood's) works otherwise OK, it
receives HF signals where it should, etc. Its MSD is well below 1µV
and its noise and intermodulation characteristics seems to be
great. I didn't run all the tests yet, especially (I must confess)
not those above 15MHz (lack of an adequate signal generator and some
other issue, see further).
Thanks also for contemplating the support for external HW through
add-on DLL. It would be nice if this one could be made "open" e.g.
by publishing a template DLL including a "how-to" cook book.
Another way of achieving communication between two programs on the
same PC would be using an IP socket (Winsock32 libraries) to
interchange messages, using "local host" as IP address (a bit of
overkill maybe).
Many thanks again and all the best,
Jean.
--- In [email protected], "i2phd" <[EMAIL PROTECTED]> wrote:
>
> --- In [email protected], "jeanrenier2004"
> <jean.taeymans@> wrote:
> >
> > [snip]
> > I am currently finishing an home build SDR receiver front end
> > project (very much) based on Gerald Youngblood's design
published
> > back in 2003.
> > [snip]
> > 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.
>
> Jean ,
>
> I have no direct experiences with that card, but there are
messages
> on various groups that report that some model from Creative have
the
> left and right channels skewed by one sample in time. Probably
this is
> caused by the use of a single ADC multiplexed between the two
> channels. Some other SDR softwares have an option to delay one of
the
> channels by one sample, to cope with this.
> Given that at 96 kHz sampling rate, one sample time is about 10.41
> usec, you could try with SDRadio to set the sampling rate at 96
kHz,
> leave the amplitude balance control at its middle, and then change
the
> phase slider adjusting it for 10.41 usec (plus or minus, you have
to
> experiment with this). Please report your results, thanks.
> >
> > 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.
> >
> Yes, this would be useful, and I have already implemented it in
> Version 1.0 of Winrad which will be released in a couple of weeks.
> Winrad now supports external hardware through an add-on DLL, the
first
> being coded is that for the SDR-14. When I will update SDRadio I
will
> add this feature also to it.
>
> > 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.
>
> This can be done using the product Virtual Audio Cable, that
> implements a direct channel between the output of a sound card
program
> and the input of another one. Search with Google for that name and
you
> will find it. And with VAC you will need just one sound card, not
two.
>
> 73 Alberto I2PHD
>
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