--- In [email protected], "Greg - ZL3IX" <[EMAIL PROTECTED]> wrote:
>
> Hi Guys,
>
> Let me introduce myself, as I am a new member to the group.
>
> My name is Greg, and my call is ZL3IX. I am interested in HF
> radio, with the 160m band as a speciality. My station is
> completely home brew and the receiver has a back end that uses a
> Motorola 56002 DSP eval board.
>
> The front end part of my radio is now very old, and I am in the
> process of building a new one, using DDS local oscillators. I am
> considering using a PC sound card as the back end for this version,
> but have never written programs for a sound card before.
>
> Could someone please tell me if there is any educational literature
> on the use of sound cards - how to write code for them, how to
> avoid timing interruptions by the O/S, whether the processing is
> done on the card or in the PC itself, etc.
>
> Your help would be appreciated.
>
> 73, Greg, ZL3IX
Hello Greg,
welcome aboard. The sound card topic is a very important one for the
SDR, at least until the ongoing HPSDR project will have released its
Mercury card, capable of digitizing at more than 135 Msps with 16 bits
of amplitude resolution. The data will then be sent, after decimation,
to the PC through the USB 2.0 interface, and the sound card will stop
obsessing all the SDR experimenters... :-)
Until then, here are some considerations, in no particular order.
- The sound card is used only for its ADC and DAC functions. No
digital processing whatsoever is done on the card,
- The amplitude resolution is important to determine the dynamic range
of the final product. The best cards have 24-bit ADC, though those 24
bits are just nominal. With the best the market can offer, you can
hope for 110 dB of dynamic range.
- The card is not directly accessed by the user program (otherwise it
would be a nightmare to offer support for the hundreds of cards
present on the market), but via one the software interfaces offered by
the operating system. Speaking of Windows (maybe others could spend
some words about Linux), the two major interfaces used are MME (Multi
Media Extensions) and DirectSound. You can find the relevant APIs
(Application Programming Interface) both described on Internet or in
some specialised books. And you can browse the source code of my
program Humid (which stands for Hum Instant Destroyer....) which I
have just uploaded in the Files section of this group. Look under the
I2PHD folder. Humid is very simple, it reads the incoming audio
stream, applies a comb filter at multiples of either 50 or 60 Hz, and
resends the audio data to the sound card for real time playback. Maybe
it can be useful to see how the MME APIs can be used. And you can also
follow the suggestion of Tilman, and have a look at the source code of
Linrad of Leif SM5BSZ, both the Linux and the Windows versions.
Good luck with your projects !
73 Alberto I2PHD
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/soft_radio/
<*> To unsubscribe from this group, send an email to:
[EMAIL PROTECTED]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
