Digital Modes Page 5

Copyright © 1999-2011 by Harold Melton, KV5R. All Rights Reserved. Feel free to link.

General Operating Notes

  • Your soundcard clock may be sloppy. All modes will work better if you calibrate it. Use SSTV or FAX software, tuned in to WWV. Set software to a mode with a scan rate (LPM) that is 60 or some harmonic of 60. Adjust radio so WWV tick paints clearly in software program. Adjust soundcard sample rate so tick line is perfectly vertical. You can get within 1 part per million accuracy if you are patient. Record the new settings and error rate. Apply exact sample rate or error correction PPM to all your soundcard programs that will allow it. MMSSTV has the best soundcard calibration utility I’ve ever seen.
  • Don’t use VOX, else you end up with Windows noises illegally on the air (and it irritates the crap out of others). Furthermore, if you use the aux mic input on the radio, and you happen to have the radio keyed (talking), any sound the computer makes will also be transmitted. This may be handy for voice contesting, but otherwise will be playing “music” over ham radio. Any time the computer output is connected to transceiver, you should tuen off all computer sounds. Go to Control Panel, Sounds, and set Scheme to “No Sounds.”
  • Digital modes that use audio modulation must be completely clean. Do not overdrive! If you see ANY ALC, that’s too much! Dummy-load your signal and listen to it with another receiver. Make sure it’s 100% clean. You’ll see dirty, splattering signals on the air, right on waterfall display: A splattering PSK31 signal can interfere with 10 QSOs! Avoid QRO operation. Use modest power that is 100% clean. There must be no clipping or ALC anywhere in the audio chain. Avoid reactance devices that might reshape the waveforms. Never use speech processor or compression.
  • Adjust computer mixer volumes to mid-points, then adjust radio mic gain to normal, then AF gain to normal listening level, then adjust interface pots. Do not expect good signals either way if you have pinched the computer mixer way down. The mixer needs to be fairly open so the software can see a large range of binary numbers coming from the soundcard. Don’t overdrive the soundcard hardware and expect a software mixer to fix it. Likewise, set the computer audio output at a modest level so the output transistors are always on but well below clipping. Most soundcard software drive the soundcard very hard by sending it the full 16-bit range of numbers. Some allow you to adjust the digital ouput going to the soundcard.
  • PC Mixer mixups: Most have two modes: Record and Playback. For INPUTS (mic and line and sometimes aux), the RECORD LINE IN will set the level going into the software. The PLAYBACK LINE IN will set the monitor level. Monitor must be muted if you use VOX, or received audio will loop through the computer and key the radio! (Yes, in spite of antivox). That’s the best reason to build a comm port keying interface, monitor the radio through the radio speaker, and the PC through the PC speakers. PLAYBACK LINE OUT or WAVE sets the output level.


I do not have much experience with logging software, but if I ever start contesting, I’ll just use MixW.

Software: 2003: MixW does it all. Full-featured logger with normal and contest modes, several statistics screens, uses standard ADIF files. MixW can be your main and only logger. Takes input manually and from CAT (radio control connection).

2002 Update: Logger is still the best free logger (IMHO). Unfortumately, HamScope still doesn’t write to it directly — but HamScope does write ADIF files which can be imported into Logger.

Software: WriteLog $75. CW keyer, RTTY, and PSK31 are built-in. Can be networked for multi-op contests. This is called “the ultimate contest logger for Windows.” Even has crossed-bananas and auto-tune. I have not tried it.

Contest Voice Keyer

Since the computer is already connected to the radio, automating repetitive voice messages (like “CQ Contest!”) is simply a matter of recording wave files and setting some buttons and repeat interval options to play them.

MixW, and several loggers, provide this capability.


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