[linux-dvb] Re: signal noise ratio and signal strength

[Holger Waechtler <holger@convergence.de>]

Hi Alessio,

the current API defines signal strength and SNR as values in 10^-6 dB or 
dBm. This was originally defined by Nokia but is not implemented by most 
frontend drivers since the hardware delivers a value between 0...127, 
0...255 or 0...65536 and most doc's don't specify how these map onto the 
logarithmic scale.

In most cases you want the limited range anyway. We are working on some 
changes in the driver, I'm currently porting some of the frontend 
drivers to a new API, where we defined both signal strength and SNR to 
be kind of linear within 0...65536. I'll post a RFC about the frontend 
and DiSEqC API changes next days on this list, but until the 
implementations go into the public driver we still need some time.

We can't simply change the API because it was submitted as part of the 
LinuxTV standard definition; we'll probably have to release a version 2 
of the API. Suggestions about changes are welcome.

- Holger


Alessio Sangalli wrote:
> Hi. I've written few weeks ago asking for an explanation of a couple of 
> calls to the DVB API; probably everyone had to work hard (or perhaps too 
> many chocolate eggs around) so I try to ask again:
> 
> I'm using the FE_READ_SNR and FE_READ_SIGNAL_STRENGTH calls to the DVB 
> api. I can read the values but I have a question: I'd like to know the 
> range of values I can read from those calls. The minimum and the 
> maximum, the meaning of the values, if positive and negative values are 
> legal...
> 
> thank you
> as
> 
> 
> 
> 
> 
> 
> 
> 




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