Star Trek and Packet Radio?

Posted: 4th December 4, 1989 By: Bob McGwier, N4HY
Several months ago, Harold Price, NK6K, challenged me to demodulate what
he thought might be HF packets in Star Trek IV. During the
scenes where Scotty is valiantly trying to beam both Chekov and Uhura back
from the U.S.S. Enterprise, where they have been stealing Nuclear vessel
high speed photons, Scotty is having a hard time hearing them.
One of the sources of interference is what appeared to Harold to be HF
packet. Always being one to rise to a challenge, I took on the job
of doing some fancy Digital Signal Processing footwork. Almost
from the first I was certain that it must be an HF packet since my
very first demodulator attempt clearly revealed flags before the start
of a frame and end of frame was also clear. I knew it was HDLC of some
variety.
Several things impeded the effort, including Scotty's voice on top
of the packets, some SSB from 20 meters was also nearly on top
of the signal. All of this had to be filtered out. I spent an hour of
time on the Cray-2 at work and used the fanciest FSK demodulator I could
write and I finally had noisy baseband signal plotted on paper in front of
me. I did my best to get an integral number of samples per baud
as the signal was very noisy, and though the bits could be made out by
eye, I could tell that it was going to take another hour of Cray-2 time to
get the clock recovered and to make good bit decisions. In a couple
of places, HDLC showed me what were clearly bit errors, and these could be
done by eye as well.
After the filtering, and
building a demodulator for the badly mis-tuned signal (it was almost 900
Hz below ormal'), I took the bits to Phil Karn, KA9Q and he decoded the
NRZI data and proved beyond a shadow of a doubt that it was indeed an HF
amateur radio packet. It was WA8ZCN-0 sending an RR for NR-3 to N6AEZ on
20 meters. I got Bill Harrigill, WA8ZCN on the phone and he agrees that
it was probably him.
Thanks Harold for the challenge and Phil for the help. Bob N4HY
P.S. A Cray-2 is about 50% faster than the fastest Pentium-Pro
computer available today.
____
Welcome to our Techical Site. If you are interested in an overview, then visit our
Marketing Site
Copyright © 1994-2005
Radioactive Networks ,
darryl@radio-active.net.au
This page was last updated 2005-09-01 09:14:59
This page was last compiled 2005-11-15 19:12:57
Question or Comment? Click
here
|