Based on observations of the tones on the waterfall on the air, compared
to observing them locally, and hearing the raucous tones compared to
bell-like quality locally, my guess is that perhaps the modulation is
disturbed or the tones moved in frequency far enough so there is no
decoding. If we try to use DominoEx, which is very tolerant to drift,
the Doppler distortion also stops DominoEx from decoding. MFSK16 is not
usable, because the Doppler shift is so great that tuning is lost and
the AFC cannot follow it. It is not unusual to see a slow Doppler shift
of 50 Hz to 100 Hz on 70cm, but the most severe problem is a fast
Doppler distortion which is present almost all the time and destroys the
integrity of the carriers, at least as it is possible to hear and see on
the waterfall.
I can't compare ROS on HF to UHF, except for monitoring, as it is
illegal to transmit on HF, but monitoring on HF does not show the same
problems. I have seen ROS signals start printing garbage on HF in a QSB
fade and then recover when the fade ends, but there is no published
specification for the minimum S/N that the 16 baud variation is supposed
to work at. Even when there is no QRM, I have seen decoding of ROS 16
baud, 2250 Hz width, stop at metrics of -8 dB. If this corresponds to
S/N, then the 16 baud version does not compare favorably with Olivia or
MFSK16, which can work 4 dB to 5 dB lower.
My guess is that the problem is not because the spreading in ROS is too
little, but on UHF, that the tones themselves are disturbed in a way
that makes ROS just print garbage when Olivia is still printing quite
well. ROS stopped decoding today even when SSB phone was about Q4 copy,
and under those conditions Olivia prints without any errors.
Unfortunately the way it is now, we are unable to successfully use ROS
on UHF, for whatever the reason, and it is illegal to use it on HF under
FCC jurisdiction.
That is too bad, because ROS is definitely fun to use.
73 - Skip KH6TY
w2xj wrote:
If there were documentation on ROS then there would the possibility of
investigating the problem further and maybe adding improvements. Part of
the problem is that even if there is a large degree of spreading
compared to the data rate, the channel is still quite narrow and a large
portion of it subject to the same disturbances or interference. This is
similar to what happens with the various commercial broadcast digital
systems. The wider ones are much more robust, especially in regard to
multipath, even though the data payload was increased in proportion.
KH6TY wrote:
> > Simon HB9DRV wrote: There's a lot more to Olivia than being
> multi-tone MFSK.
>>
>>
>>
>>
> I am aware of that, Simon.
>
> However, Olivia is currently the most popular digital mode other than
> PSK31 and RTTY, and the question was if ROS 16 baud was worth using
> twice the bandwidth of Olivia. We hoped that it would be, because on
> UHF, space is not at a premium as it is on HF, but ROS 16 baud, (the
> spread spectrum variation) at 2250 Hz width, was not even as good as
> SSB phone under the fast Doppler flutter conditions. So, as a choice
> of modes currently available, either MFSK16 (my personal preference on
> HF, but impractical on UHF due to the necessity to tune so accurately
> and have little or no drift) or Olivia, is a far better choice than
> ROS, and performs better.
>
> We would like nothing better if there were a mode that outperformed
> Olivia at equivalent typing speed, and could copy further into the
> noise than Olivia can, and is more tolerant to mis-tuning or drift
> than MFSK16, but so far ROS is not the one. As things stand, CW
> (decoded by ear) is currently the "last mode standing", but it seems
> it must be possible to come up a mode that can beat CW under the
> typical conditions found on UHF.
>
> 73 - Skip KH6TY
>
>
>>
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>
