I need Another Serial Port!

By Chuck Rexroad, AB1CR

With the modern era of Ham Radio, most of us use PCs in some aspect of our hobby.  We may operate PSK-31, MSK, packet, or have our PC control our rig or rotator.  What most of us do is wonder why we always need more serial ports than we actually have.

For the last few years the Universal Serial Bus (USB) has been on virtually every PC made (desktop or notebook).  I have looked longingly at the USB to serial interfaces, but they simply cost more than I was willing to pay.   Thanks to the ubiquitous Palm Pilot and other PDAs, there is now a simple, cost effective solution for those who need another serial port.

The USB PDA adapter from Keyspan connects to the USB port on the PC and provides one DB-9 type connection.  The adapter costs about forty dollars, which is more than an additional serial board, but with far fewer headaches.  There is no need to buy a serial card, open the PC, or go through what is often a significant configuration challenge.  Installation is simply “Plug and Play”, and there is no manual setting of Com ports, IRQs, or any of the other fun things normally associated with adding a serial port to your PC.  In my case this means that I can now operate PSK-31 while using my logging software to control my rig and running WinAPRS.


As with many consumer devices, the installation procedure is not well explained.  Do NOT start by hooking up the hardware to your PC.  This can cause significant damage to your current configuration files.  Also, do NOT start by dropping the CD into the tray and letting it install itself.  The manual, included on the CD ROM, states that one should not install in this fashion, but there is no icon for reading the manual until after the installation has been completed.

The best way to install the USB PDA Adapter is to put in the CD ROM in (do not connect the PDA adapter yet), and when it asks if you want to install, just say no.  Then go to Start, Run, Browse, D (or whichever drive is your CD) and run the setup program.  (This is the Keyspan’s recommended setup process, although it is somewhat unusual.)  Once this is complete you will need to reboot your PC.  Only after the reboot is completed should you plug the USB PDA adapter in.  Windows will load the proper drivers and configuration, and you are ready to use your new serial port!  The only question now is, what’s it called?

Go to Start, Settings, Control Panel, System, then click on the device manager tab.  Now expand the section on Ports (Com and LPT).  You will see a window and a new port called Keyspan Com Port (COM x), where x is the Com port number that Windows has assigned the new com port.  Simply configure your software to use this COM port, hook up the appropriate device to the new serial port, and you’re good to go!  Note, if your software does not allow using the newly assigned COM port you may want to think about using the new COM port for a different function and using your original hardware/software on one of the original COM ports.  In my case, I originally planned on doing DX Cluster through the new adapter, but the DOS version of Log-EQF (or any DOS based program for that matter) could not use the new com port.  Digipan didn’t mind the new COM port a bit, so I moved my Rig Blaster to the new COM port and I had accomplished my goal!


I have done compatibility testing with the USB PDA adapter with a number of programs and devices.  Most Windows based software will allow hooking up to the USB adapter if it will work under Windows with your original serial ports and the software will recognize the Com Port of the USB PDA adapter.

The Keyspan USB PDA adapter works with Windows 98 and higher, and also supports Mac.  I have not done any testing with the Mac environment.   I have seen discussions of Linux support in some of the Linux newsgroups, but as yet I have not seen anyone provide this support.

In case of difficulty

There may be situations where you need to set the properties of the USB PDA Adapter within the Windows control panel.  Most software packages will override these default settings, but in my testing I did have to set the defaults for at least one combination of equipment.  To set the defaults in Windows Control Panel, follow the steps above to get the screen where the Keyspan Com Port is shown.  Single click on the Keyspan COM Port and then click on the properties tab.  Select the Port Settings tab and then set the following parameters:

(NOTE:  These values will work for most packet and GPS configurations.)

Final Notes

The Keyspan USB PDA adapter is available from a wide variety of sources.   Shop around for the best price.  Keyspan also makes a 2-port version of this adapter, but that was not tested for this article.  For those with serious com port needs, there are also four-port USB to serial adapters, but they require a much bigger checkbook!

One final thought.

The USB PDA adapter is meant to be connected and disconnected at will.  This means that if you also have notebook PC that you want to use for APRS mobile, you may well be able to use the USB PDA adapter in the car and have two serial ports on your PC.  One will connect to the TNC and the other to the GPS.  As you can see, the possibilities are endless!