Part 1: Hardware and Software
 n the fall of 2001, I presented a program to PARC on the use of a sound card digital interface for the transmission and reception of PSK-31 signals. At that time, I was just beginning to get interested in other modes that are conveyable by such a device. I hadn't yet discovered multimode software and the added flexibility that came from using it. There have been several changes in my strategy since then.
Virtually any common operating mode can be run through one's computer, depending on how much work you want to go to use it. It makes things convenient for contest operation, since a lot of the computer logging programs are also set up to use the interface as well. It can even be used for voice contest work, since it is possible to make .wav files of common exchange information and CQ and QRZ calls; making such things a whole lot less strain on one's pipes. Other modes that are commonly accessible through the interface include SSTV, CW, and all of the teletype modes, not to mention Hellschreiber. By teletype modes, I'm referring to PSK, RTTY, AMTOR, PACTOR (if you want to shell out serious money for the software), MFSK16, WSJT, and others too numerous to mention.
From the September, 2001 meeting program, AL7W expounds on PSK-31. This is but one of the many operational modes that is facilitated by inter-facing with a sound card. Virtually anything that can be transmitted or received is
interfaceable.
Hardware:
The basic circuit for my interface hasn't changed, other than to set it up so that CW keying of the radio can be done with a second opto-isolator. A case for making the level controls accessible has also been made, for optimizing receiving levels (apparently, one size does NOT fit all).
The computer that works with the interface needs to be a Pentium class or newer computer, and some of the software out there requires something huskier than a Pentium 100 with 32 MB of RAM running Windows 95 (which is what I use in my shack).
The connections between the interface and the computer are pretty much the same: The line level input and output of the sound card go to receive and transmit audio respectively, while on one of the com ports, DTR goes to the keying interface, DSR goes to the PTT line, and Ground is common to both on the computer side of the chips. The transformers in the interface and the opto-isolators eliminate the possibility of there being ground loops between the computer and the radio. Level control pots are included on the signal lines to adjust the interface for optimal signal transfer.
Unlike my previous interfaces, this one uses jacks on the interface itself to disconnect the cables. That way, if something should happen within one of the cables (as has happened to me), it's not a major teardown and rebuild to replace the offending wire. It also allows the interface to be hooked into the accessory jacks of different brands or models of radio, or into the mike jack, if you prefer (most rigs' mike jacks also now include a receive audio line-level signal right on the microphone jack). Those cabling details are left up to the individual and his radio.
Software:
There is a whole panoply of software for sound card interfaces out there, most of it for the PC platform (Mac and LINUX program information would be welcome, and if provided will see the light of day in a future article). Originally I was working with DigiPan for PSK-31. As a single-mode application it's a good one, although there are partisans for other single-mode programs out there like
WinPSK and some FT-817-specific applications. For RTTY, I'm somewhat partial to
MMTTY. I've used that application frequently in RTTY contests, and while there is some transmit/receive delay, it seems to do the trick rather nicely. I've also used
MMSSTV, with good results (anyone want to do a program on slow scan TV?-Ed.). Lesser results came from using the
Stream software for MFSK-16. The interface is clumsy, and it's hard to set up. The one time I used it, I was directed to a good multi-mode program.
The multi-mode programs have kind of come into their own over the past couple of years. I'll mention two that I've used, and what I discovered about them when I did. The first one I tried was
HamScope. That one really needs a huskier computer than I tried it with. It has a tendency to bog things down and not to work very well after a while. It does do PSK-31 and MFSK-16 and
RTTY, but the version I tried didn't have radio interface controls for the IC-735. It wanted a Pentium 200 or faster and at least 64 MB of RAM. I had neither. It also only interfaces directly with one rather expensive logging program. From there I went to the big brother of
DigiPan, MIX-W. It does everything, including voice. About the only modes I know of that it doesn't cover are PACTOR for transmit (proprietary software, rather expensive), and the weak-signal VHF software
(e.g.: WSJT). As a jack of all trades, it has its moments of mastering none. It is also shareware, with a $50 registration fee.
Some of the single mode software works better.
MIX-W does, however, have its uses, and it is convenient if you want to go mode-hopping. Not mentioned here are the contest software packages such as
WriteLog, whose RTTY and PSK interfaces are reputed to be rudimentary.
It has become a lot more practical for things to be automated, and the sound card interface is the easiest way to get that job done. It is no longer the province of the green-key geek, as it used to be. Digital modes are fun, and the interface also allows the repetitious tasks of phone and CW to be accomplished by keystroke, rather than by screaming your lungs out. For less than $20, it's worth doing! Interface construction details will appear in next month's issue.
-AL7W
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