[time-nuts] nubie querie

[Hal Murray]

Concerning my query about what's good enough to count as a contact...

> We've done Moonbounce with 3mW (Hobart - Dwingeloo) in JT65 - but a
> 26m and a 25m dish is stretching 'amateur' a bit again. 

Googling for JT65 finds a nice paper:
  http://www.arrl.org/FandES/field/regulations/techchar/18JT65.pdf
  The JT65 Communications Protocol
  Joe Taylor, K1JT

It's a fun read.  17 pages.

The basic idea seems to be that amateurs (hams) have to exchange station IDs. 
 That's more than a few bits, but not a huge number.

JT65 is a compact protocol for doing that in a (very) weak signal 
environment.  Their packet format is 72 bits expanded to 378 by forward error 
correcting.  On top of that, they use half of the time for a synchronizing 
signal so the receiver can find the transmitter's time and frequency.  Each 
72 bit packet takes 1 minute to send.

Their modulation scheme is 1 of 65 tones.  6 bits per baud.  The extra tone 
is the synchronizing signal.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.