[aprssig] 9600 Baud Packet Network?
Stephen H. Smith
wa8lmf2 at aol.com
Sun Jun 12 14:56:40 CDT 2016
On 6/12/2016 1:13 PM, Robert Bruninga via aprssig wrote:
>> I once tried... a 320x240 SSTV-like image over packet.
>>... it took over 15 minutes to send one image.
> Agreed, but at 9600 baud it might take only 3 minutes.
Actually, once you take into account the overhead of RX-to-TX and TX-to-RX
turnaround and TXD issues on radios not optimized for rapid-fire data
transmission and the relatively short packets involved, the net throughput is
not likely to be dramatically better. Add to that the reduced tolerance for
low signal strengths at 9600 (i.e. you have to have stronger signals (i.e.more
power, more antenna or both).
>> Classic packet is dead - the infrastructure isn't there anymore....
> People know how to text on their phone. Is it possible to have an app that
> looks similar on the phone but can talk to a serial port and a packet network
> as a backup?
Smartphones don't have serial ports. You will have to deal with all the
complexities of serial-->USB-->serial bridges. Serial-interface hardware TNCs
are passe. Far easier to do this with software TNCs that use the audio system
of the device as a TNC.
I'm running the application "Pocket Packet" on my iPad now. This is a
full-blown APRS messaging/mapping client that uses the iPhone or iPad sound
system as a soft TNC. It can also connect to the APRS-IS via either WiFi or
cellular data if available. It "automagically" uses the device's GPS if available.
The easiest off-the-shelf platform for this, due to the wide range of software
available, is the cheap Windows 7" and 10" tablets available for under $80 (and
sometimes for under $60). These devices run standard desktop-type Windows in an
ultra-compact form factor.
To send pictures, you use the tablet's internal camera(s) with standard Windows
SSTV programs like mmSSTV (analog) and EasyPal (digital) that use the device's
sound system. For text traffic, use the freeware FLdigi program which operates
a vast variety of modes (RTTY, PSK, MFSK, Olivia, MT-63, and coming soon -
300/1200 baud packet). Just connect the tablet's mic/headphone jack to the
6-pin MiniDIN "data" port (actually audio in/out) on most radios.
The companion program to FLdigi, "FLmsg", produces
fill-in-the-blanks-and-hit-send forms for ARRL traffic, MARS, FEMA incident
command system, Red Cross, etc The companion FLarq app provides full
handshaking error-corrected ack/nak transmission.
With "EasyPal" running on one of these tablets, I can shoot and send a 800x600
pixel high-quality image in less than 2 1/2 minutes NOW. (EasyPal is actually
a general-purpose error-correcting file transmission system. It uses 4, 16 or
64 QAM audio subcarriers simultaneously within the standard SSB-type audio
passband to achieve throughput equal or higher than 9600 baud packet. It can
send text documents, spreadsheets or any other kind of computer file as well as
"SSTV" images.) It can automatically FTP received files to Internet servers if
desired. On the air, if some of the transmitted blocks are defective, it can
request re-transmission. The re-transmission (ARQ) can even come from a third
station that heard the blocks successfully - a real advantage on HF where
shifting propagation and skip zones prevent some stations from hearing each
other, but both can hear a third one.
Running the UZ7HO "Soundmodem" program lets me use EXACTLY the same hardware as
a 300/1200/2400/9600 baud TNC for APRS applications, or even as a stand-alone
Or run "Airmail" which uses the FLdigi app (or it's own softmodem) to access
the Winlink system.
All this is done with existing off-the-shelf hardware and software NOW. No need
to re-invent the wheel with "kludge box" controllers/interfaces with magic
mystery code in them.
Review of the TW700 sub-$60 Windows tablet here:
> We seem to have lots of people wanting to write code on their favorite little
> $35 processor, why not level 4 code to use all these radios in KISS mode to
> build a 9600 baud backbone network between EOC's at least.
> It is sure better than a bunch of old fuds reading ARL radio grams and spelling
> every word during a comex.
Trying to do this with 9600 baud packet is beating a dead horse.
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