On 8/1/2019 1:27 PM, James Wolf wrote:
I think there is some misunderstanding of bandwidth using FT-8.
The power limited Shannon limit I posted about today is
independent of equivalent noise bandwidth
The equivalent noise bandwidth of an FT8 detected tone is only 6.25 Hz. So
-26 dB S/N ratio in a 2500 Hz bandwidth is 0 dB in a 6.25 Hz bandwidth.
Thus using the conventional version* of the Shannon limit, the
maximum theoretical bit rate is 6.25 bits/second. FT8 supposedly can
do about this rate at -24 dB S/N in 2500 Hz. IOW, it is within 2 dB
of the Shannon limit.
This is all self consistent.
*At a SNR of 0 dB (Signal power = Noise power) the Capacity in bits/s is
equal to the bandwidth in hertz, according to Wikipedia.
Rick N6RK
Jim Wolf, KR9U
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
|