[mythtv] What units of SNR is returned by FE_GET_SNR

[Taylor Jacob]

Quoting Mac Michaels <wmichaels1 at earthlink.net>:

> I send this to both linux-dvb and myth-dev lists because SNR
> is generated by a linux-dvb driver and displayed by the
> mythtv application while doing a tuning scan.
>
> I have searched the DVB documentation for the units of
> signal-to-noise ratio and found only that is is an int16_t.
> Not much help. SNR is usually specified in db and defined
> as:

Each DVB driver does it differently.  There are no units because on many demods
that have been reverse engineered no one knows what the units really are.

Here is one example.  The value can be 0-0xFFFF.  I did some checking and found
that 32DB is very very high for ATSC reception and so I made the SNR value for
the Nxt2002 go from 0 (0db) - 0xFFFF (32db).

The Hd2k/3k cards report the value as just the actual unit so 32db would be
0x0020.

Great system right?   There really isn't much of a way to fix this other than
hope the drivers return some reasonable value..

Taylor