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Re: [PATCH] FM1216ME_MK3 some changes




Dmitri,


On Wed, 2009-04-22 at 17:48 +1000, Dmitri Belimov wrote:
> Hi All
> 
> 1. Change middle band. In the end of the middle band the sensitivity of receiver not good.
> If we switch to higher band, sensitivity more better. Hardware trick.

This concerns me slightly as it does not match the datasheet (hence the
design objectives) of the FM1236ME_MK3.

How are you measuring sensitivity?  Do you know if it really is the
middle-band preselector filter (and PLL and Mixer) or is it a problem
with the input signal?  How do you know it is not manufacturing
variations in the preselector filters with the particular tuner assembly
you are testing?

Also, as an alternative to using a different frequency for the
bandswitch, have you considered setting the Auxillary Byte in the tuner
chip (Infineon TUA6030?) to use external AGC and experimented with
changing the tuner AGC take-over point (TOP) in the TDA9887?

By maximizing the gain in the tuner chip, but avoiding clipping, with
the proper TOP setting, you minimize the contributions by the rest of
the receive chain to the overall receiver Noise Figure:

http://en.wikipedia.org/wiki/Friis_formulas_for_noise

This may be a way to improve receiver sensitivity that does not conflict
with the data sheet specification.




> 2. Set correct highest freq of the higher band.

:)

This bothers me too; all the tuners in tuner-types.c have it set too
high (999.0 MHz).  I think I rememeber at time when all the tuner_range
definitions had a real value there.

It would be nice to have a real value there for all the tuners.  The
function tuner-simple.c:simple_config_lookup() would then prevent
attempts to tune to an unsupported frequnecy.



> 3. Set charge pump bit

This will improve the time to initially tune to a frequency, but will
likely add some noise as the PLL continues to maintain lock on the
signal.  If there is no way to turn off the CP after the lock bit is set
in the tuner, it's probably better to leave it off for lower noise and
just live with slower tuning.

Leaving the CP bit set should be especially noticable ad FM noise when
set to tune to FM radio stations.  From the FM1236ME_MK3 datasheet:
"It is recommended to set CP=0 in the FM mode at all times."
But the VHF low band control byte is also used when setting FM radio
(AFAICT with a quick look at the code.)

Regards,
Andy

> diff -r 43dbc8ebb5a2 linux/drivers/media/common/tuners/tuner-types.c
> --- a/linux/drivers/media/common/tuners/tuner-types.c	Tue Jan 27 23:47:50 2009 -0200
> +++ b/linux/drivers/media/common/tuners/tuner-types.c	Tue Apr 21 09:44:38 2009 +1000
> @@ -557,9 +557,9 @@
>  /* ------------ TUNER_PHILIPS_FM1216ME_MK3 - Philips PAL ------------ */
>  
>  static struct tuner_range tuner_fm1216me_mk3_pal_ranges[] = {
> -	{ 16 * 158.00 /*MHz*/, 0x8e, 0x01, },
> -	{ 16 * 442.00 /*MHz*/, 0x8e, 0x02, },
> -	{ 16 * 999.99        , 0x8e, 0x04, },
> +	{ 16 * 158.00 /*MHz*/, 0xc6, 0x01, },
> +	{ 16 * 441.00 /*MHz*/, 0xc6, 0x02, },
> +	{ 16 * 864.00        , 0xc6, 0x04, },
>  };
>  
> 
> 
> Signed-off-by: Beholder Intl. Ltd. Dmitry Belimov <d.belimov@xxxxxxxxx>
> 
> With my best regards, Dmitry.
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