[linux-dvb] Re: How to determine the frequency of a channel

[Holger Waechtler <holger@convergence.de>]

Carsten Koch wrote:
> Martin Neuditschko wrote:
> ...
> 
>>But the result is not which I wanted because the "FE_HAS_LOCK"
>>appears very often but there is no audio or video.
>>
>>Here a small example:
>>Frequency: 377758000
>>status 00 | signal 9090 | snr d6d6 | ber 00012eec | unc 0000007f |
>>status 1f | signal ffff | snr eded | ber 00012eec | unc 0000007f | FE_HAS_LOCK
>>status 1f | signal ffff | snr ecec | ber 0002c3d8 | unc 00000000 | FE_HAS_LOCK
>>status 1f | signal ffff | snr eded | ber 0002c3d8 | unc 00000003 | FE_HAS_LOCK
>>status 1f | signal ffff | snr ebeb | ber 00013335 | unc 00000000 | FE_HAS_LOCK
>>status 1f | signal ffff | snr ecec | ber 00013451 | unc 00000002 | FE_HAS_LOCK
>>status 1f | signal ffff | snr eded | ber 00013451 | unc 00000000 | FE_HAS_LOCK
>>status 1f | signal ffff | snr ecec | ber 00013057 | unc 00000000 | FE_HAS_LOCK
>>status 1f | signal ffff | snr ecec | ber 00013057 | unc 00000004 | FE_HAS_LOCK
>>status 1f | signal ffff | snr eeee | ber 00012f50 | unc 00000002 | FE_HAS_LOCK
>>status 1f | signal ffff | snr ebeb | ber 0001316d | unc 00000001 | FE_HAS_LOCK
>>status 1f | signal ffff | snr ecec | ber 0001316d | unc 00000001 | FE_HAS_LOCK
>>status 1f | signal ffff | snr ecec | ber 0001345f | unc 00000000 | FE_HAS_LOCK
>>status 1f | signal ffff | snr ecec | ber 0001345f | unc 00000001 | FE_HAS_LOCK
>>status 1f | signal ffff | snr ecec | ber 0001318e | unc 00000000 | FE_HAS_LOCK
>>status 1f | signal ffff | snr ebeb | ber 0001332a | unc 00000000 | FE_HAS_LOCK
>>
>>How else could I try to determine the best frequency?
>>Has someone an idea?

best SNR and lowest Bit Error Rate are indicators for a good working 
point. Another approach would be to scan the whole range, then take the 
center point of the working interval.


> I'd say go for the one with the strongest signal an the
> best signal to noise ratio. But apparently the signal 
> strength indicator is at maximum already and the snr
> does not vary much. I wonder if that can be improved in
> the driver, so you get useful values?

No, when the AGC circuit works in saturation the driver can't do much 
more than read out these saturated values. Try to use a signal 
attentuator between cable plug and DVB card input to get your signal in 
a lower range.

Holger





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