Hello All,
There is simple answer why users prefer operate JT65 on the overloaded HF bands
while there is underused JT9 subband.
.
Anyone from DX location, let's say for instance from New Zealand, have
frequently met scenario where multiple signals coming back to his CQ call.
.
Due to the nature of JT9 protocol&modulation neither one of two JT9 signals on
the same frequency will be decoded in most cases, things getting worse if there
are more than two signals on the same frequency. To make QSO possible
experienced JT9 users call DX stations with frequency split and DX station in
response has to use split operation or frequency hopping.
.
Now one could imagine if there is propagation open between Europe and New
Zealand and at least 10 operators calling one DX station using frequency split,
this way JT9 spectral benefit versus JT65 is almost eliminated.
.
Multipass decoding will only work if at least one JT9 signal is decoded on the
frequency, otherway there is nothing to subtract.
.
Now back to JT65 HF subband capacity, for evenly distrubuted JT65 signals
between -01 and -26dB SNR to the Gaussian noise, maximum JT65 current subband
capacity is around 100...110 decoded signals if tested with 200 simulated
signals in the .wav file. These decoded signals have SNR to the Gaussian noise
in range from -01 to -14 dB, week signals gone unless DX operator using 1kW
power to try getting through.
.
For last 45 days number of JT65 HF users raised 25% up, and it is now usual
event to get 35..40 decoded JT65 messages for single RX interval. Going with
such increase rate monthly we will get out of the current JT65 HF bands
capacity within 6 months, and similar to PSK modes, high power usage will
became as common behaviour.
.
Hence there no other way to save HF JT weak signal communication but an
increase of the occupied bandwidth and it should be good idea to act now, until
we got to QRO JT communication instead of the weak signal one.
.
73 Igor UA3DJY
------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, SlashDot.org! http://sdm.link/slashdot
_______________________________________________
wsjt-devel mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/wsjt-devel
