[RTTY] Multiple Decoders

[Kok Chen]

On Feb 1, 2012, at 6:26 AM, Ed Muns wrote:

> Many of us have been doing multiple decoders for years now, particularly the
> DXP38 plus multiple instances of MMTTY with different profiles.

Some of us have used this for years now without even knowing they are actually using multiple decoders :-P.

The RTTY demodulator in cocoaModem consists of 9 separate RTTY decoders.  Each one with a different ATC profile, although sharing the same Mark and Space filters.  Instead of printing all 9 outputs, a majority vote is performed and the most likely decoded Baudot character is printed to the screen.  

All these 9 decoders work from a single audio stream (sound card) from the receiver.

So, it is like having 9 sub-modems, but you don't get to see all 9 outputs to decide for yourself which one is correctly printing.  You only get to see what the software thinks is the correctly decoded character.  Like democracies, the majority is not necessarily correct, but they are correct more often than they are incorrect (that is also why democracies work :-).

In addition to that, cocoaModem has two of these built-in RTTY demodulator sets.  

Each set is completely independent from the other, each with its own waterfall, crossed ellipse indicator and modes (reverse, baud rate, tone pair, etc).  And each one has its own Mark and Space filters. These two "receivers" can be "connected" (menu selection) to two different sound cards, or, if you like, can be connected to the same sound card to give you 18 sub-modems, working off two different Mark and Space filters.

The two sound cards can be connected to two different receivers, with the receivers coming from the same antenna, or coming from different antennas for visual diversity reception (experimenting with auto diversity decoding is in some planned future software :-).

Almost always though, I connect the two modem sets to two channels of a sound card that are connected to the main and sub-receiver of my rig for split-DX chasing.  But other ops have the choice of connecting both to the same sound card.

73
Chen, W7AY