[aprssig] High speed modems?

Stephen H. Smith wa8lmf2 at aol.com
Mon Jul 18 12:42:45 EDT 2016

On 7/18/2016 4:04 AM, SARTrack Admin via aprssig wrote:

> This is a bit off topic, but I have been asked (and not for the first time) if
> there is a way to do emergency communications on VHF/UHF at reasonably medium
> to higher speed.
> My SARTrack software can do some of the work via APRS, but due to the
> connectionless state, it is not very suitable for reliabe transfer of critical
> data, and it is way to slow.
> I have users who are now looking at DMR for data transfers (because they
> already use commercial DMR radios for Voice and GPS location data) but these
> radios are by default very narrow-band, and are aiming more towards the 6.26 kc
> bandwidth than to 25 kb bandwidth, let alone more.
> What we really need is a fully digital VHF or UHF radio modem, which enables us
> to do make one-to-one connections, and possibly some kind of one-to-many data
> transfers.
> Looking at the TAPR website, most of the things I find there are very old.  I
> would like to find some kind of system which uses the latest technologies to
> get the most data over a bandwidth which can still be used in VHF/UHF.
> If there is a mailing list more suitable for this topic, please let me know.
> Thanks,
> Bart ZL4FOX
> http://www.sartrack.nz/

With a minimal sound card interface and a small tablet, you can run the FLdigi 
suite of applications which includes numerous modes that can achieve data rates 
up to 1000 chars/sec in SSB bandwidths on HF; i.e. 2.5-3 KHz.  It should be 
effortless to run these modes over any conventional analog FM radio link on 

Teamed up with the companion IP-linked  "FLmessage", you have 
"Fill-in-the-blanks-and-hit-SEND" standard forms for many reporting formats 
including ARRL radiograms, Red Cross, MARS, (US) Incident Command System 
reporting, etc.   The companion "FLwrap" program allows you to encapsulate ANY 
kind of computer file in an FEC/ARQ container that can be transmitted 
guaranteed error-free over any of the FLdigi modes. Finally there is "FLamp" 
(FL Amateur Multipoint Protocol) that allows you to broadcast one-to-many 
FEC-encoded announcements and bulletins repeatedly to multiple stations at 

There is an "NBEMS" (Narrow Band Emergency Messaging System) initiative going 
on now in the US among EMCOMM/ARES/RACES types, to adopt the FLdigi suite 
widely for both HF and VHF backup to Internet and cellular data in emergency 
response scenarios.

I have been told that in the near future, the main FLdigi app is going to add 
standard 300/1200 baud packet to it's present vast array of modes (CW, 
Contestia, Domino, FSQ, Hell, MFSK, MT-63, Olivia, PSK, QPSK, 8PSK, classic 
RTTY, etc).  In most of these modes, you can use either use the internal basic 
split screen send/receive terminal, or use the program as a KISS TNC to link to 
external programs.  The addition of AX.25 packet means FLdigi can become a soft 
TNC to any APRS application.

I have the entire FLdigi suite (along with a ton of mapping and APRS apps) 
crammed onto a $65 7" Windows tablet.   It connects, via the headphone/mic 
combined jack, to any of my radios via a homebrew soundcard interface.  The 
interface is completely self-powered by rectifying the TX audio tones generated 
by the tablet speaker line; no batteries, 12 VDC power, serial or USB ports are 

I have used this setup with a Wouxun KG-8UV dual-band handheld, a Kenwood 
TH-D72, a Yaesu FT-857, a Kenwood TS-690, and on my TS-2000 on both the primary 
SSB radio and the secondary VHF/UHF-FM radio.

Details on the tablet here:

Details on the tone-keyed soundcard interface here:

Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

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