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Sound Card Packet

Excellent Tutorial!
Ralph Mines (KC2RLM), wrote this tutorial, not just for SoundCards but for all configurations with Packet Engine.Thank you Ralph. It is also available in Francais and Portugese.


SoundCard Modems
Your SoundCard, the one you are using now, has a build in DSP chip. Using this chip we can receive and transmit packets in ,almost, any baudrate. For the moment AGW Packet Engine supports 300b, 1200b and 9600b.

Tuning Win7 Drivers for maximum sensitivity
1. Right click on task bar speaker icon and select "Recording Devices".
2.
3. Select the Soundcard you use for Packet. I select "Behringer".
4. Press [Properties].
5.
6. Select the "Advanced" Tab and open the Format List box.
7. Now select the baudrate Quality Packet Engine Pro uses.By default is 44.100 for VHF and 11.025 for HF.
8. Finished.
9. Now the windows driver will not make conversions. If the Quality was 11.025 and you have 1200b VHF modem then Windows will convert internally the 11.025 to 44.100 and as you can understand this will affect the quality of the sampling.

Problems to Solve
Since we are running under windows it is impossible to access directly the SoundCard, unless we write a special driver. But writing a special driver we will prohibit the usage of the soundcard by other programs. The only way to use the soundcard is to use the build in MIME API. Using it we don't interact with the soundcard but with the soundcard driver. So the performance of our DSP code depends on the soundcard driver. So always search for newer drivers. Another problem is the processor power. DSP algorithms need power, so a Pentium with enough RAM (at least 64Mb for win98) is a must. The last problem to solve and the most important is the switching between transmit and receive. In Packet we must switch between TX/RX very fast so if your computer is not fast enough it is possible to hung up transmitting. Why this happens?? Lets see how we transmit a packet frame. We start processing the frame data and convert them to DSP data, when the DSP data are enough we send them to the Soundcard driver for TX, while continue processing more data. When the driver finishes tx the first chunk of data notifies us about this and we send it more. If our computer isn't fast enough we may still process data while the driver finished TX and that way we aren't able to process the driver notification. The result is that we wait for ever for this lost notification. The situation for SSTV and Filter programs is quite different, since we don't have so fast switching between TX and RX and also the TX time is large enough. So PSE don't shoot the Programmer, try to find a faster driver or computer!!. A way to increase your computer's speed is to check for the follow... Reduce the programs that are running, especially those hidden, like antivirus programs. Press [CTRL+ALT+DEL] to see the programs currently running.

How to Configure it
First of all decide how to control your transceiver ptt. If Ok then select the appropriate Serial Port or Parallel Port. Now be careful, this driver can be used for 300b,1200b or 9600b, so we must inform the driver which speed we wish. So select the appropriate baudrate in the Baudrate field.
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