--- In digitalradio@yahoogroups.com, Alan Beagley <ajbeag...@...> wrote:
>
> It seems to me that the developer of the mode may have cooked his own
> goose: he declared it to be a spread-spectrum mode, and spread-spectrum
> is mot legal on HF in the USA.
In spite of what author claims, ROS is not a spread spectrum mode. Spread
spectrum definition said that the SS signal is spread over the much wider
frequency band (orders of magnitude) than the bandwidth minimum required to
convey the intelligence. Let's take a pencil and do some math to check this
with Shannon-Hartley law for channel capacity:
C = B log2 (1 + S/N), where C ---- channel capacity in bps, B ---- channel
bandwidth in Hz, S/N ---- signal to noise ratio.
ROS1 mode is capable of 21 characters per second and -30 dB S/N. Assume we have
7 bit characters. So, it's 21 * 7 / 60 = 2.45 bps. S/N = (-30 dB) = 0.001. The
required channel bandwidth to transmit 2.45 bps with -30 dB S/N ratio will be:
B = C / log2 (1 + S/N) = 2.45 / log2 (1 + 0.001) = 1699 Hz
It's not hard to see that 1699 Hz ~ 2250 Hz. With this example it needs to be
at least 17 kHz for name it spread spectrum.
> 73
>
> Alan NV8A
73 Ivan UR5VIB
