[RTTY] ROS

[Kok Chen]

On Jun 12, 2010, at 11:23 AM, John Barber GW4SKA wrote:

> A search later got me to the Southgate ARC site where the frequency for this mode is stated to be 14101 and I found out it was just another data mode. Does anyone know more about where they operate, 14097 or 14101?

14.0972 MHz and 14.102 MHz according to this page.

http://hamchatforum.lefora.com/2010/02/26/a-youtube-video-shows-ros-the-new-digital-mode-des/

> If ROS is magically robust it should work round my RTTY!

Not if you are 90 dB louder than them :-).

If you transmit a loud RTTY signal in the middle of a Pactor III signal, you would wipe them out too.

ROS implementers shot themselves in the foot by calling it "spread spectrum," thus making it illegal to use by USA hams on 2m and lower ham bands. On paper, it is really no worse than any other multi-tone FSK digital modes that uses 2 kHz of bandwidth, just that the ROS "encoder" includes a pseudo-random "spreading function" -- i.e., typing "W7AY" twice will produce two different encodings of the string.  The decoder needs to know the "spreading function" to recover "W7AY" each time instead of being able to directly look in a Baudot or Varicode table.

Notice that it uses 2 kHz of bandwidth to transmit a 1 (one) baud of data rate.  You can fit an entire PSK31 contest within a single ROS signal :-).

ROS also has very low spectrum efficiency (apparently by design).  Take a look at a spectrum captures that Skip KH6TY made comparing ROS spectrum to MFSK16 spectrum.  Notice the wasted holes in the ROS spectrum.

http://home.comcast.net/~hteller/SPECTRUM.JPG

73
Chen, W7AY