we discussed the topic a bit on a somewhat recent thread:
Well after buying a Satlink meter It has a db and BER readout. The signal qualitt readout on it is pretty useless as it is always between 60 to 69 on all locked transponders. I never paid attention to db and ber but am learning by using this meter and have to say it is very helpful...
www.satelliteguys.us
my take away is that the Signal Quality in % is relevant only within your receiver. In other word, on a given signal, one receiver might say 70% and another receiver connected to the same dish might say 50%. I suspect it has to do with what the manufacturer decided 100% would be. If they decided 100% was a 20dB SNR, then you would rarely get above 80%, and anything above 50% would be good signal. But if they decided 10dB would make 100% quality, then a 90% signal might not work (depending on the modulation and FEC). I'm intentionally exaggerating a bit. The bottom line is that you should use the quality only to fine tune your dish to get the highest number, but you should not worry about comparing that number with others.
As mentioned above, the modulation and FEC dictate the minimum SNR required for locking a signal. 8psk requires more SNR than QPSK, and the closer then FEC is to 1, the less capable it is at correcting the errors, so it requires a cleaner signal. Note that usually, common wisdom is that DVB-S2 requires a higher quality than DVB-S, but that's not exactly true. DVB-S2 often uses more demanding modulation and FEC (8psk, 3/4 or 5/6), but a QPSK DVB-S2 signal can work with a lower SNR than a similar DVB-S signal. It's just that we don't see many QPSK, low FEC DVB-S2 signals out there.
check out these lists for minimum SNR:
www.satbroadcasts.com
www.satbroadcasts.com
