[aprssig] High speed modems?

[Derek Love]

DMR should give you 9600 bps in a 12.5 kHz channel, but that is a raw rate and assumes that you've concatenated the two TDMA slots (which I'm not aware of any manufacturer doing, but...).  But the "normal" single slot modes would still give you 4800 bps raw, and the DMR spec allows for raw, 3/4 and 1/2 rate FEC, so for a raw mode you can achieve 3600 bps payload transfer rate. That's already three times faster than 1200 APRS, considerably more when you take the APRS overheads into account. If you can make use of both slots, that would give you 7200 bps.... or are you thinking of considerably more than that?

Derek Love, CML Microcircuits, Systems Group
+44 1749 881130

-----Original Message-----
From: aprssig [mailto:aprssig-bounces at tapr.org] On Behalf Of SARTrack Admin via aprssig
Sent: 18 July 2016 09:05
To: TAPR APRS Mailing List
Subject: [aprssig] High speed modems?

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/

--
Bart Kindt
SARTrack Developer and CEO
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