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[email protected]

On Thu, 29 Nov 2018 02:23:09 -0500, wrote:

On Thu, 29 Nov 2018 00:59:42 -0500,
wrote:

On Wed, 28 Nov 2018 18:48:18 -0500, wrote:

IBM collected a lot of hams. Back in the days when I was in DC they
were already migrating to digital, hooking ASR33s (teletype) to their
ham gear. Some still worked 2 meter radio telephone but not that much.
The guy from Ft Myers who retired in Tennessee says they have a pretty
active ham group there but they are connecting up PCs.
I guess ham has become just an RF modem.

===

Digital comms is sort of on the cutting edge of ham technology these
days although it goes back more than 15 years at this point. There is
a device called a Pactor modem which acts as a combination modem and
packet encoder. It attaches to either a ham rig or commercial marine
tranciever, and allows error free transmission at speeds up to 4800
baud under good conditions. It's fairly sophisticated in its
operation, automatically adjusting speed and re-transmissions based on
radio conditions and error rates. I use it when we are cruising in
the boondocks for EMAIL, weather, stock market quotes, etc.

http://www.docksideradio.com/ptcii.htm

We ran 4800 BPS modems here in Ft Myers to get to the office network
from home. As long as you were just using text and maybe some low
resolution pictures it worked great.
When the V.32bis (~14.4Kbps) and V.34 (19.2Kbps) stuff showed up we
were awed.
I am surprised they can't get that trellis modulation stuff running on
RF. We were doing it on nasty dial up lines at 2400 baud. (not the
same as bps)
The baud is 2400 (basically the frequency of the carrier and about all
dial up can deal with) They then pick off 8 data bits from every wave.
(19.2)
4800 bps is only looking for a bit at each peak. (2x baud). Maybe RF
can't beat unshielded copper.

They get away with higher rates by using better error correction
algorithms. A clean line will run at the rated speed and it starts
falling off fast from there. At a certain point the modem will kick
down to a lower speed until it finds one that works. That sounds like
what you have too.
Cool stuff tho until they get the couple hundred satellites they want
up for broadband connections.

===

The Pactor speeds are limited by FCC regulations designed to minimize
bandwidth and adjacent frequency interference. Of couse HF SSB is
also much noisier and susceptible to fading than a telco landline. The
automatic re-transmission of error packets and adaptive signaling is
very cool however, and quite useful for short messages, weather data,
etc.

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