In the APRS world a new piece of software has been creating some excitement. It is a soundcard modem for packet radio by UZ7HO. It runs under Windows and emulates the AGW Packet Engine so that it can be used by any program that is designed to work with it. The reason for the excitement is that this packet modem can decode several packet signals on slightly different frequencies in parallel, resulting in many more decodes on HF where it is quite common for stations to be 50Hz or more off-frequency.
Andrei UZ7HO’s sound card modem currently has the following features:
- 1. 300 or 1200 bd packet operation, configurable by port.
- 2. Supports internal Soundcards or external USB Soundcards
- 3. Runs under XP. Vista or Windows 7, without any need for installation.
- 4. Uses existing preinstalled device driver files for soundcards
- 5. Emulates SV2AGW packet engine, in TCP mode and can be used as a direct replacement.
- 6. Dual Channel operation, for unconnected nets.
- 7. Supports multiple decoder pairs per channel (explanation later)
- 8. Supports Com port 1~10 or parallel ports 1~3 for PTT triggering
- 9. Supports VOX (in the case of Signalink Modems)
- 10. Menu config for basic settings
- 11. .ini file for extended options
The software is still in beta and Andrei is churning out versions rapidly as it gets tweaked. It is has become quite stable in the last few weeks as Andrei has got to the bottom of a few Vista and Win7 bugs.
The application is provided as a zipped single executable, which when extracted and placed in a folder, can be run. It needs no “installation” and creates the .ini file when the application is run.
The application provides dual channel operation and dual waterfalls, so different spot frequencies can be monitored for decoding. Either channel or waterfall can be disabled if not required. Each channel starts off as a single decoder, however, the number of decoders can be increased in pairs either side of the “standard” decoder (subject to CPU “horsepower”, the more enabled, the more resources used).
This allows parallel decoding of “off frequency” transmissions either side of the centre spot frequency. The default step, at the moment, is 30Hz per decoder pair and it is possible to add up to 16 additional decoders per channel (8 either side of the centre decoder, giving approx ±270Hz decoding bandwidth per channel on Rx (Similar effect to the SCS tracker modems) of strong signals. The decoder pairs are enabled in multiples of 2, i.e. one pair either side of the centre pair.
Note: Enabling more decoders than the CPU can handle will cause instability, this will exhibit itself as random locks of the s/w, and horizontal bars in the “quiet” areas of the waterfall.
If parallel decoding is to be used, it is better to increase the number of decoders a step at a time, to ensure reliable operation. DCD only works on the centre spot frequency.