El 18/03/2010 18:11, KH6TY escribió:
Extensive tests on 70cm using ROS 16 baud spread spectrum have been
disappointing. ROS appears to be unable to survive the Doppler shift
and Doppler induced "flutter" so prevalent on that band. The hope was
that ROS 16 baud would make traditional communications possible that
were difficult on SSB phone because of the Doppler shift and
"flutter". However, the tests show that Olivia 32-1000, in half the
bandwidth, and Olivia 16-500, produce print when ROS only prints
garbage. This, together with the fact that both stations must be
within 400 Hz of each other before even trying to communicate, instead
of being able to tune with the mouse as is possible with Olivia, makes
it very difficult to achieve a QSO on 70cm using ROS. Olivia has
therefore proven to be much more successful than ROS on UHF.
I was also dissapointed on HF. To me, ROS is an incomplete solution that
stands no comparison to other beter designed protocols already in use.
FHSS per se is not a "miraculous solution". Even when having some
processing gain, is not enough to stand and recover from the real world
path impairments.
Tests using the ROS 1 baud variation will be made next, but the slow
speed of that mode is more suited to EME communications than normal QSO's.
In two weeks of monitoring ROS 16 baud on 20m, there has been only one
observed case where the S/N was under where Olivia 32-1000 can decode,
so even on HF, there does not appear to be any justification for using
such a wide mode, even if spread spectrum were permitted on HF in the
US. Just use Olivia or MFSK16 instead when band conditions are poor.
The new narrow band ROS modes were not tested, since a mode to do
better than Olivia is what is needed, and the spread spectrum mode of
ROS held the best hope. As it stands, only CW is better than Olivia
under the worst conditions, and only when copying by ear, but CW is
only a little better than Olivia 16-500. We have also found that the
more narrow Olivia modes (i.e. < 500 Hz wide) are also too greatly
disturbed by Doppler to be useful either.
Perhaps what is needed is a variant with wider tones/bins, modulated at
a higher speed, so path perturbations have a lesser effect. Have you
tried higher bandwidth and less tones ? Maybe you can find a better
compromise (it will always be a compromise, I believe) that way.
If anyone is within 200 miles of FM02, has 100 watts and an antenna
gain of 17 dBi or greater, and would like to try ROS 16 baud on UHF, I
am available to do that.
I promised to post the results of our attempts to use ROS on UHF on
this reflector, and this is what we have found. So, it looks like
Olivia is currently still the best digital mode to use on UHF, VHF, or
HF for normal (not EME) digital QSO's.
Skip, please do tell us. I am particularly quite curious about the
results of your tests.
73,
Jose, CO2JA
