[linux-dvb] DViCO FusionHDTV 5 Lite Signal Strength?

Mac Michaels wmichaels1 at earthlink.net
Fri Mar 17 07:25:44 CET 2006


When there is a specification for the value returned as the 
result of a request for signal strength I will be glad to 
fix this. It returns zero because the API does not give 
enough guidance as to what the returned value means. Is it
a) Actual signal strength in dB as a signed integer
b) Actual signal strength in tenth's of dB as a signed 
c) Percent (of what) with values 0 to 100
d) 0 to 100 percent (of what) with values 0 to 0x7FFF
e) 0 to 100 percent (of what) with values 0 to 0xFFFF
f) Tenth's of a percent of c, d, or e
g) Something completely different like the raw AGC value 
from the tuner

The chip does not return signal strength directly. I can 
make up a number based on signal to noise ratio (SNR) which 
is returned by the chip. I don't have the test equipment 
required to accurately calibrate signal strength. I can 
make it return a number in tenths of dB similar to the 
Windows driver for the DViCO cards. The other important 
number for determining signal quality is the bit error rate 
(BER) which is also returned by the chip.

I tried returning the actual SNR in DB when I wrote the 
driver. This is a signed number. It is negative for bad 
signals and a small positive number less than 100 for good 
signals. I got complaints that it was wrong since the 
returned value is unsigned and the poor SNR negative values 
looked like large numbers while the good SNR values were 
small numbers. 

The result is raw data for values read from the chip and 0 
for values that can not be read from the chip directly.


On Thursday 16 March 2006 03:14 pm, C. David Cooke wrote:
> Hey,
> I saw in the sources for lgdt330x.c that the signal
> strength always returns 0 and that adding support for the
> signal strength is on the TODO list.  Can anyone give me
> a status on this?  What would it take to get this
> working? How can I help?
> I have one of these cards and am having problems with
> video stuttering and I'm trying to track down the problem
> - having a signal strength would really help .
> Thanks -
> David

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