Due to the effects propagation it is difficult to evaluate the parameters of a mode, particularly with detectability around the noise level.
PA0A has done Lab Tests on the ROS OPERA digtal radio data mode and found the following results.
Op1 decode @ -24dB Average from many test
Op2 decode @ -27dB Average from many test
Op4 decode @ -30dB Average from many test
Op8 decode @ -33dB Average from many test
Op32 decode @ -37dB Average from many test
This is nice to know as it agrees closely with the expected theoretical values. Odd readings are obviously the result of propagation.
Loss of Data in the signal will give abnormal S/N results. I tried removing 1/3 of the bits throughout the message, the act of doing this looks like sabotage of the correct message coding, it is, the result was just one decode from many tests of a bogus call with a marginal S/N ratio.
13:35 500 8N3CSZ de G3ZJO Op4 -30 dB in Northampton
Removing the complete mid 1/3 of the Data in the message does degrade the S/N as does removing the first 1/3, anyone can try removing the last 1/3 by stopping the transmission.
Readings with complete Data:-
14:21 500 G3ZJO de G8HUH Op4 181 km -26 dB in Somerset.
14:21 500 G3ZJO de M0BMU Op4 -15 dB in nr Hatfield
14:21 500 G3ZJO de G3ZJO Op4 0 km +6 dB in Northampton
Readings with 1/3 blocks of Data loss.
14:47 500 G3ZJO de M0BMU Op4 76 km -17 dB in nr Hatfield
14:47 500 G3ZJO de G3ZJO Op4 0 km +3 dB in Northampton
Next 1/3 of the Data was removed in blocks of 8 bits in a random fashion throughout the message again OPERA decodes successfully:-
14:53 500 G3ZJO de G8HUH Op4 181 km -28 dB in Somerset. test4
14:53 500 G3ZJO de M0BMU Op4 76 km -17 dB in nr Hatfield
14:52 500 G3ZJO de G3ZJO Op4 +0 dB in Northampton
In further tests I may try removing 50% of Data bits.