Yes but at UHF there seems to not be enough spread to tolerate the Doppler shift. If the frequencies were further apart, and were received through a wider window, the Doppler would be tolerated better but at what penalty in noise? I can think of a few ways to solve your problem but not with existing sound card modes.
KH6TY wrote: > 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 >> > >> > >> >> >> >> >> > >> >> >
