[Lowfer] Strange Stuff on 508.5

[John Andrews]

For those of you who have been wondering what all the racket has been 
recently on 508.5 kHz, Jay and I have been playing with a program 
mentioned on the ARRL site:
http://www.arrl.org/?artid=7933

No new modulation schemes are involved, and we have mostly been using 
PSK31 and PSK63, which are built-in. The NBEMS software implements ARQ 
(automatic repeat request) error correction to send files and emails in 
error-free form. Checksums are embedded in the text, and the sending 
computer stops periodically to effectively say "did you get that?". The 
other station then automatically responds with an OK to go ahead, or a 
direction to repeat something that was missed.

The banging back and forth is interesting to watch, but the only station 
who gets that error free file is the receiving station. Anyone else 
monitoring will see patterns of clear text and codes.

The obvious application for this is emergency communication, and we are 
just starting to evaluate its use at 600 meters. MFSK16 is one of the 
modes included, and we will certainly be trying that as well as the PSK 
modes. The error correction adds a lot of overhead to the data being 
sent, and the back-and-forth further slows things down.

We'll be on at 0200 UTC tonight (9 PM EST), playing with some email and 
text files. Feel free to watch, but don't be disappointed if the clarity 
is a little underwhelming. As a receive-only operator, you'll gain 
nothing with the NBEMS software, and will see exactly the same stuff on 
your favorite program.

John Andrews, W1TAG