On 8/6/2019 5:30 PM, Randy Thompson K5ZD wrote:
There are several software packages available that have taken the WSJT
decoding engine and created the ability to make multiple QSOs at the same
time. It is just a matter of sending tones on multiple audio frequencies at
the same time. This takes advantage of the narrow bandwidth of FT*
information.
Is it one signal or multiple? We could easily make the argument that it is
one signal (being sent using SSB audio tones) that contains multiple
information components.
RTTY AFSK uses two tones (mark and space) to send information. The two
tones are not on the exact same frequency. Is that two signals or one? It
has been considered as one signal forever.
I see a clear distinction, Randy. The two switched tones used to
transmit RTTY constitute a single signal. When FT4 or FT8 software
transmits more than one tone at a time, each is a separate signal.
The real problem with this practice is that considerable IM is
generated. I've observed it on the signals from expeditions that were
using it. It may be tolerable for F/H by a DXpedition when it's the only
signal on the band, but would be a train wreck in almost any other
application. W0YK made a post to this effect to the NCCC reflector a few
days ago, noting that this was demonstrated in the recent webinar.
73, Jim K9YC
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