[linux-dvb] Some thoughts and questions

Georg Acher acher at in.tum.de
Sat Sep 29 15:27:38 CEST 2007


On Sat, Sep 29, 2007 at 04:18:31PM +0400, Manu Abraham wrote:
 
> > - LNBs have a constant error plus a temperature drift
> >   (e.g. +/-1MHz error, +/-3Mhz drift for a temperature range
> >   of -40 ... +60 °C -- cheap no name equipment usually worse)
> 
> This is the old LNB, the one's we use are generally based on PLL's have
> some 15 - 20k drift

"old" LNBs? That's the majority in the consumer market. In fact I haven't
seen a PLL stabilized LNB until now in that area. Even the "high quality"
consumer stuff made by Invacom have no PLL and just a simple DRO pill for
the LO.

> even a max of 20k is so small within the actual bandwidth window, for a
> demod not to lock A demod has a bandwidth of normally 5 - 10 MHz,
> depending on the device.

This is only true if you have high symbolrates. On the STV0299, a 3MS/s
transponder tolerates just about 500-800kHz drift. 

-- 
         Georg Acher, acher at in.tum.de         
         http://www.lrr.in.tum.de/~acher
         "Oh no, not again !" The bowl of petunias          



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