Choosing a Pactor modem
Short answer: The modem you want is the PTC-IIusb.
Long answer: SCS currently offers three Pactor modems: PTC-IIusb, PTC-IIpro, and PTC-IIex. All perform equally well in terms of radio communications, and all are available with the Pactor-3 upgrade (which we recommended for use with Sailmail). The differences are radio frequency-control, connection to the computer, and support for packet modes. Packet is not used by Sailmail, but frequency-control and the computer connection are important considerations. The PTC-IIusb and PTC-IIpro both include a radio-control port which allows the computer to set the radio frequency without manual tuning. As discussed below, this is highly recommended. The PTCII-usb modem (as the name suggests) connects to one of the computer's USB ports, while the PTC-IIpro and PTC-IIex modems require a 9-pin serial "COM" port which most laptop computers no longer provide.
So our recommendation is the PTC-IIusb modem, with the Pactor-3 upgrade. The PTC-IIpro offers the same basic functionality but does not have a USB connection, and costs more. The PTC-IIex is less expensive, but does not provide either radio frequency-control or a USB connection. There are other ways to connect things but the cost and complexity are greater than for the PTC-IIusb. (Note that older computers prior to 1999 did not support USB and usually have a serial port. In this case consider a new computer- they don't last forever- or a PTC-IIpro).
Frequency Control:
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Why the big deal about frequency-control? Sailmail currently operates 18 stations, each with 5 to 10 frequencies-- nearly 140 different frequencies total. Successful communication requires using the appropriate frequency for your location, time of day and radio propagation. The Airmail software provides a propagation window which makes frequency selection quite easy- just click on a propagation chart and the frequency is automatically set on the radio... IF there is a remote-control connection from the computer to the radio. And therein lies the problem with the PTC-IIex.
The PTC-IIusb (and the PTC-IIpro) modem has a "control" connector (in addition to the audio connector) which allows the software to set the radio frequency. Cables are available for virtually all SSB radios.
The PTC-IIex does not provide radio frequency control. While there are other ways to do this it makes the system more complex and complexity is the enemy of reliability. The simpler the configuration the more reliable it will be. For a PTC-IIex, without some other radio-control connection, the alternatives are to either set each frequency manually, or to pre-program the radio memories with the frequencies for each station. Either approach is laborious and will limit your ability to quickly select an appropriate frequency.
If you do have a PTC-IIex then we recommend a serial-port connection to the radio for frequency-control. This can be done by adding a USB/serial adaptor (discussed below) and a control cable from this adaptor to the radio. The Icom-M802 uses a simple serial-extension cable to the radio's "REMOTE" connector, the M710 requires a specially-wired cable (part# ____).
Computer serial ports:
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The issue with the computer connection is that laptop/notebook computers are generally no longer available with serial "COM" ports. Instead, high-speed "USB" ports are used to connect peripheral devices. The advantage of USB ports are that they are faster, largely self-configuring and more flexible. The few computers with serial COM-ports are generally legacy designs, even if your current computer has a serial port the next one will probably not.
The PTC-IIusb modem, as the name suggests, is a modem that connects directly to the computer's USB port. The required drivers are included with the Airmail software and also on the CD shipped with the modem. If the software is installed first then the modem can simply be plugged in and will automatically install, or it can be installed from the CD. In either case installation is generally trouble-free.
The PTC-IIpro and PTC-IIex connect to a 9-pin serial port (as does the radio-control cable for a PTC-IIex). For most computers this requires a USB-to-serial adaptor, either a single-port "dongle" or a multiple-port adaptor box. While there are lots of different brands available, many of the less-expensive adaptors are not reliable. Our recommendation is to stick with the Keyspan, SIIG or Edgeport adaptors, available from many modem dealers, Farallon (www.farallon.us, the US SCS distributor) or from www.cdw.com. The Keyspan model USA-19HS single-port adaptor is available from www.cdw.com for around $30. For a PTC-IIex you will also want a second port for radio control, either use two single-port adaptors or a multi-port Edgeport adaptor. The Edgeport adaptors are available in 1, 2 or 4-port versions (or more), this is industrial-quality gear and the cost will be higher- but the reliability is correspondingly higher. Again these may be available from your modem dealer, Farallon, or from CDW.
Bottom line: Get a PTC-IIusb. If you have a particularly old computer that doesn't support USB, then consider getting a new computer and then a PTC-IIusb. A PTC-IIpro will work equally well with a USB-to-serial adaptor, it just costs more. And if you have a PTC-IIex then we strongly recommend adding another serial port and a remote-control cable.
If you need help with this then start with the dealer who supplied the modem, or (in the US) contact Farallon Electronics (1-415-331-1924 ext. 112). Sailmail members can also contact Sailmail tech support at support@sailmail.com or 1-619-980-6215.