[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
> 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.
> Bart ZL4FOX
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
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
EchoLink: Node # 14400 [Think bottom of the 2-meter band]
Home Page: http://wa8lmf.net
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