I was in the USAF from 1968 to 1972 but did not work in communications (more along the lines of security, HI). It was not until a few years after I was relicensed in 1980 that I got involved with digital modes buying a Model 15 and making a simple TU promoted by the ARRL as a state of the art TU even though knowledgeable digital ops knew it certainly was not anything of the sort. But I did not realize it until I started using it. It did work acceptably when its primary use was on our local RTTY 2 meter regenerative repeater system, but on HF it was close to unacceptable in performance. I built my own homebrew loop supply and even borrowed a tube TU loosely based on the ST-6 design.
No one was happier than me to get away from the noise and smell and mess of TTY hardware when the computer became affordable with the Commodore 64 and interfacing. The main modes were RTTY and Amtor, the first digital amateur ARQ mode. Other modes followed and we saw improvements in error free transmissions with Pactor and Clover II. After selling everything digital to come up with enough money at the time to buy the HAL P-38 ISA board for my IBM 286, I was forced to completely quite HF digital modes when I returned (at a loss) the pathetic P-38 which never was able to properly operate Pactor. In fact HAL would not even call it Pactor and referred to it as P mode. The main digital mode became packet on VHF, but then the invention of PSK31 changed everything. Hardware modems were no longer necessary, not even the alternative separate DVM 5600x series outboard units. You could do it with just the sound card. The sea change was quite large and hardware modems became mostly obsolete except for the high end SCS units which are still sold to a few who mostly use it for e-mail. The new modes that were developed after PSK31 have not been so much better that there is a wide spread movement to them. Some are better than PSK31 for some purposes, but when you factor in all the parameters for the average casual operator, PSK31 does well. No other mode is as narrow for the speed. It may not be very resistant to doppler or interference but when conditions get bad, the majority of hams turn off the radio and do something else rather than attempt to get through with modes that can handle those kinds of conditions. The way that the modes stack up for me for practical use: PSK31 - the most commonly used mode where you can almost always make a contact 24/7 on some HF band at any given time. If you actually used a digital mode to make an emergency communication contact, this would be the first choice over all other digital modes assuming you would actually use digital modes over tactical voice which is preferred for this purpose. MFSK16 - moderately narrow mode, critical tuning, thus requires accurate sound card calibration, works much better into the noise than PSK31 and is one of my preferred modes. Olivia - more robust with interference and sometimes with weak signals but requires a combination of very slow throughput and/or very wide bandwidth to maintain the robustness. Also, there are so many combinations that it can be difficult to quickly match the baud rate and number of tones from the other station and you may miss them. FAE400 - currently the best ARQ sound card mode by far. No other SC ARQ mode can come close to the convenience, weak signal ability, relatively narrow bandwidth, and speed along with quasi duplex operation (no need to have an "over" command). If I could only have one SC mode, this would be the one. However, it is rarely used since it is only available on Multipsk and most hams don't have a need for error free contacts. I try not to use modes wider than 500 Hz in the narrow RTTY/Data portions of the bands as I consider it to be very poor operating. The one exception is wide band ALE which is 2000 Hz and it probably should only be used in the phone/image portions of the bands and then for initial contact. The speed is very slow for the wide bandwidth and it is not very robust. I realize that the thinking is to include hardware backward compatibility, but this is an older legacy mode (developed in the 1970's for voice channelized commercial/government use) and newer modes such as FAE400 would be far better for amateur use as a more appropriate ham friendly technology that uses a similar waveform. The other criteria for me is that the mode must at least work at 30 wpm or better. Anything slower is too slow to interest me. Some digital operators may have modest or even very slow keyboarding skills and would find slower modes acceptable to them. 73, Rick, KV9U
