mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2024-09-19 19:56:33 -04:00
23aff84fbb
* Moved doc/source/*.txt to AsciiDoc ext source/*.adoc - Correctly identifies AsciiDoc files * wsjtx-main.adoc - Updated links and include:: for *.adoc name change * Added and updated rig-config-* files. * Added inital draft of quick-reference.adoc * build-doc.sh - Updated the script to build new files and .adoc name change * Removed: - yaesu.txt rigtemplate.txt rig-configuration.txt git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@3662 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
39 lines
2.0 KiB
Plaintext
39 lines
2.0 KiB
Plaintext
// Status=review
|
||
|
||
The JT65 protocol was described in a {jt65protocol} in 2005; details
|
||
of the JT9 protocol are presented in the next section of this Guide.
|
||
To users already familiar with JT65, the most striking difference
|
||
between the two modes is the much smaller occupied bandwidth of JT9:
|
||
15.6 Hz, compared with 177.6 Hz for JT65A. Transmissions in the two
|
||
modes are essentially the same length, and both modes use exactly 72
|
||
bits to carry message information. At the user level the two modes
|
||
support nearly identical message structures.
|
||
|
||
JT65 signal reports are constrained to the range –1 to –30 dB. This
|
||
range is more than adequate for EME purposes, but not enough for
|
||
optimum use at HF and below. S/N values displayed by the JT65 decoder
|
||
are clamped at an upper limit –1 dB. Moreover, the S/N scale in
|
||
present JT65 decoders is nonlinear above –10 dB.
|
||
|
||
By comparison, JT9 allows for signal reports in the range –50 to +49
|
||
dB. It manages this by taking over a small portion of ``message
|
||
space'' that would otherwise be used for grid locators within 1 degree
|
||
of the south pole. The S/N scale of the present JT9 decoder is
|
||
reasonably linear (although it’s not intended to be a precision
|
||
measurement tool). With clean signals and a clean nose background,
|
||
JT65 achieves nearly 100% probability of correct decoding down to
|
||
S/N = –22 dB and about 50% at –24 dB. JT9 is about 2 dB better,
|
||
achieving 50% decoding at about –26 dB. Both modes produce extremely
|
||
low false-decode rates.
|
||
|
||
Early experience suggests that under most HF propagation conditions
|
||
the two modes have comparable reliability. The tone spacing of JT9 is
|
||
about two-thirds that of JT65, so in some disturbed ionospheric
|
||
conditions in the higher portion of the HF spectrum, JT65 may do
|
||
better. JT9 is an order of magnitude better in spectral efficiency.
|
||
On a busy HF band, we often find the 2-kHz-wide JT65 sub-band filled
|
||
wall-to-wall with signals. Ten times as many JT9 signals can fit
|
||
into the same frequency range, without overlap.
|
||
|
||
|