JQAM possible use for NBTV DATV

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g8byi
Posts: 23
Joined: Sat Mar 08, 2008 5:23 pm

JQAM possible use for NBTV DATV

Post by g8byi » Thu Jun 13, 2013 3:11 pm

Ok I will be the first to add a message re NBTV DATV.
Its obvious NBTV DATV is what we are going to need to develop due to the way the frequency allocations are GOING! I am thinking preferably @ 100KHz or less for talking head use, not HD 3d stuff, not yet anyway...
A few years back I came across JQAM sw written by a New Zealander named Jonti a non radio ham , but a clever chap - into dsp and software generation. JQAM used a 96KHz sound card to send and receive data at up to 400KHz by implementing QAM modulation at up to 64 QAM.

Features:
Speeds up to 400kbs with a sound card.
QAM16 and QAM64
Eight state TCM encoding.
Between 1% and 50% Interleaved RS forward error correction.
Blind equalization, frequency tracking.
Blind carrier frequency and symbol rate detection.
Packet type of data structure.
Able to perform multimedia streaming (sound and video).
Able to send files in continuous rotation with unused bandwidth (sending of web page type content).

http://homepages.paradise.net.nz/peterfr2/QAM.htm to go to the web page

Now I did communicate with Jonti the author and he made many changes and improvements to his sw, since I said radio hams would find it very useful program. Indeed I used it at an audio bandwidth of 80KHz on the sound channel of GB3UT and sent moving video and sound through the sound channel. You need a linear broad band Tx of 100KHz bandwidth to get minimum buffer overflows but it does work . As an experiment I did try normal rigs using the 9.6Kbuad inputs but that was very limited in frequency throughput, file transferring worked and text messages could be sent. I see the site is still there (see link above) but he has not progressed it from version 3.2.Indeed he has probably moved on in life, but this technique may be a way of getting digital nbtv going over a wider bandwidth than the normal 2.5KHz -8KHz 32 line digital NBTV for HF.
Anyway its one possible minimal hardware method to perhaps build upon. I am not a programmer apart from simple stuff , so hopefully there are others of like minds out there that could start to think about this method.

73
Richard G8BYI

G4GUO
Posts: 728
Joined: Tue Feb 16, 2010 12:51 pm

Re: JQAM possible use for NBTV DATV

Post by G4GUO » Thu Jun 13, 2013 4:55 pm

The modem he mentions of mine was a sound card based V.32 modem and I was able to
achieve about 12 kbits on a standard 9k6 radio. I also used the BBCs open source video
codec called Dirac (named after Paul Dirac). To send about 4 frames per sec video.
For audio I used the Speex codec, the world has moved on a long way since I did this
work about 14 years ago.

Although it worked, using off the shelf Amateur Radios of the time it was a bit of a
dead end. Unfortunately there is no way to avoid Shannon's law so you might be able
to cram a lot of data into a small space but there is a penalty you have to pay.

My modem did not use blind equalisation but instead inserted training symbols into
the waveform and used decision feedback equalisation using a gradient algorithm.

You may find this video interesting http://www.youtube.com/watch?v=HVFFq44UvLA

FWIW Here is a screen shot of the program

- Charles
Attachments
QAM.JPG
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