Adding Computer Serial Ports (revised 2009-01-03)
The simplest way to add serial ports to a computer is with a serial-port adapter connected to a computer USB port. Before making decisions consider the use of the computer and whether additional serial ports will be wanted for radio frequency-control, a GPS connection for charting, automatic position reporting, weather fax, etc.
There are two basic types of USB serial-port adapters. One type is a single-port "dongle" to convert one USB port to a single additional serial port. These have a couple of drawbacks. One is the basic nature of "dongles", with a short cable connecting to a relatively bulky male/female 9-pin connectior. The other is that each adaptor only provides a single serial port per USB port. Most computers come with two (or more) USB ports and a USB hub can be added for more, so this is not a serious limitation.
The other alternative is a multi-port serial-adaptor box, with a single USB cable to the computer. These are available with 2, 4 or 8 ports. Besides providing additional ports for radio-control or a GPS, these have the advantage that the rat's nest of serial-port cables for the modem, radio-control, GPS, etc can all be buried in a cabinet along with the adaptor box, with only a single skinny cable to the computer-- no more "spaghetti" behind the laptop.
The "Edgeport" boxes (from Inside Out Networks, www.ionetworks.com) work well and are highly recommended. These are available from www.cdw.com and elsewhere, at a cost which ranges from $130 for 2 ports to $360 for 8 ports. If your computer is running Windows-7 drivers are included, just plug it in. Otherwise check the website and make sure you have the latest drivers.
Edgeport also makes a single-port adaptor that is recommended but has a relatively high cost, around $60.
Our other recommendation for single-port "dongles" is the "Keyspan" adapter (model 19HS) which gives consistently good results on most computers. These are inexpensive ($30-40) and available from www.cdw.com and other outlets, but not generally available in most computer stores. There are no Win-7 drivers yet but the Keyspan Vista drivers have been tested with Win-7 and work fine. Be sure to run the Keyspan setup program BEFORE plugging in the adapter, otherwise you may need to get into device manager and uninstall it and try again.
Keypan also makes a 4-ports serial box, model USA-49WG for around $160, but we don't have any experience with that model. The older model 49WLC works OK with Airmail but has problems updating modem firmware. .
There are lots of cheap USB adaptors with bad drivers which will not work properly, or (worse by far) make your computer unstable. Many problems have been reported by users of Belkin, Aten and other off-brand single-port dongles, as well as D-Link and Quatech's QSU-series boxes. Some of the cheapest single-port adaptors also omit the RS232 control lines (requiring that Airmail's "Ignore CTS" option be set).
There are two important issues to keep in mind when using USB ports: One is to make sure that you have the latest drivers, and the correct version for your operating system. If in doubt, go to the manufacturer's website and download the current drivers This is especially important if you have the latest version of Windows, verify that the drivers are labeled for that version, and are preferably "digitally signed". If you see a warning message, stop and check- lots of grief can be avoided by installing the correct drivers. The new Windows versions have safeguards to avoid errors, don't bypass them.
Finding the port numbers: One issue whenever serial ports are added is finding the correct COM-port numbers. Airmail will show you the installed ports (according to Windows) when you expand the COM-port selection list (click the little arrow). Additionally, the Windows name for the selected COM-port is shown below the com-port and baud-rate selection boxes. The built-in port is always first (if it exists) and is usually COM1, called "Communications port". If the computer has a built-in telephone modem that will be listed also, usually as COM2 or COM3, and any additional ports will be at the bottom of the list. So one easy way to check is to open Tools/Options prior to plugging in the port, and note the COM-port numbers. Close the Options window and then plug in the US port or box and re-open the options window. The USB port(s) will appear as new COM-port numbers.
Alternately open Windows Device Manager (under Control panel/System) and find the "Ports" category and expand that. All ports will be listed, showing COM-port designations. (Note: the telephone modem also uses a COM-port number but is listed here separately under "Modems"). With Device-manager open, unplug the USB port and watch for the list to update, then plug it back in and check again.
Where to buy? One obvious choice is the dealer who supplied the modem, most are familiar with adding serial ports and will be able to supply the right parts and provide support. For those who like the adventure of doing it themselves, our advice is to stick with the name brands and either buy from a high-end computer store (if there are any left) or by mail from the internet. Discount "brick and mortar" computer stores seem to carry a vast array of off-brands which are nothing but trouble with little support available. We've had good luck with CDW (www.cdw.com)-- good web site, OK prices and they ship when they say they will. Check the manufacturer's web site before you buy, make sure there is a link for "support", and check for drivers for the product you are contemplating for your particular version of Windows.
Also note that many computer USB ports are quite sensitive to RF interference, and ferrites between the modem and adaptor, and between adaptor and computer are strongly recommended.