Don't know if you're a "linux guy" or not, but the "snooper" package available on Debian Linux and derivatives, and certainly available
Thanks for the reply Nate, I'm not a Debian user (dare I admit to being a loyal Mandriva supporter?) and as soon as I can establish an Internet connection I'll search for snooper.
I've been thinking some more about this serial problem and wondering if the radio might be at fault or, more likely, that I should be doing something between read frequency commands.
If I read the frequency once per second while spinning the tuning knob, occasionally I'll see an incorrect value. That same value persists until the knob is moved again. I can see the problem but not the answer.