PACKET RADIO: Setting Your Deviation

Steve Wolf, W8IZ@W8IZ

(This text from the W8IZ packet radio bulletin

board. It's formatted to fit a 80 character screen.)

Received at NCARC PBBS July 29, 1989


No -- this is not a comment on morality! I'd like to point out to all
that if you are having trouble with your AFSK-FM packets getting thru on
VHF, check your deviation! Time and time again we have seen that stations
that sound "loud" have problems. Typical VHF radios come from the factory
set for 5 to 7 kHz deviation. This is too wide! You will find that you
get best packet performance when the deviation is cranked down to around
3 kHz. When you run "wide" the distorion in the typical FM receivers is
horrible. This was re-discovered today by one of the major area BBSs who
had been having trouble with a couple of links. On cranking the deviation
down, link performance went from marginal to solid.

If you have access to a deviation meter, use it. If not, listen to your
packets on another radio. Crank down the radio's deviation pot or your TNC's
TX audio level pot while sending packets until what you hear starts
getting weaker. This will be about 5 kHz, so keep cranking it down a bit
more and see if your performance doesn't improve noticeably. Don't worry
if your packets aren't the loudest ones on the channel. Everyone else is
probably too wide.

73, Tom



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