Some tentative ideas for section 8. OK to change, delete, etc.

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6377 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
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Steven Franke 2016-01-10 00:42:26 +00:00
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@ -2245,14 +2245,46 @@ MAP65
Mention two-pass decoding. Mention two-pass decoding.
\end_layout \end_layout
\begin_layout Standard \begin_layout Subsubsection*
Experience with FT on crowded HF bands. Experience with FT on crowded HF bands:
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
Re Figure 5 - just playing around with ideas. (Re the following paragraph and Figure 5 - just playing around with ideas
May not be appropriate for this paper. - feel free to change, delete, etc.)
\end_layout
\begin_layout Standard
The JT65 mode has proven to be remarkably versatile.
Thousands of users regularly use the mode for two-way communication over
straight line-of-sight paths and the earth-moon-earth (
\begin_inset Quotes eld
\end_inset
moonbounce
\begin_inset Quotes erd
\end_inset
) path at frequencies from VHF to microwaves, and over multi-hop ionospheric
reflection paths at HF.
Use on HF was not originally an intended application for the mode, but
at present HF use accounts for the largest number of 2-way contacts.
Figure 5 is a spectrogram with frequency in Hz on the horizontal axis showing
JT65 activity during a one-minute time-segment (JT65 transmissions start
at the beginning of a minute and last for approximately 47 s).
The data was collected in the 20m amateur band during daytime under crowded
band conditions.
With some straightforward signal processing to demodulate the signals and
produce soft-symbol data for the FT decoder it is possible to extract and
decode 21 messages from the data summarized in Figure 5, and this is achieved
with a relatively small timeout parameter
\begin_inset Formula $T=1000$
\end_inset
.
Using exactly the same pre-processing, but without soft-symbol information
the errors-only BM decoder is able to decode only 12 messages.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard