[linux-dvb] Some thoughts and questions

Manu Abraham abraham.manu at gmail.com
Sat Sep 29 15:34:53 CEST 2007


Johannes Stezenbach wrote:
> On Sat, Sep 29, 2007, Manu Abraham wrote:
>> Johannes Stezenbach 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
> 
> If you make that 20kHz per °K then it's about the usual range
> for Ku Band, maybe slightly better than average.
> (An LNB with +/-20KHz drift over the full temperature range
> would be ridiculously expensive.)

ACK

didn't account for the / K. But still for a LNB with 27 K, It amounts to around +/- 0.5MHz
Which is still quite small for a 5 - 10 MHz window.

As you said, maybe there are really bad ones with +/-1MHz drift, but i think
+/-3MHz is a bit too exaggerated figure

> 
> Don't forget that your tuner also has maybe +/-50ppm tolerance.
> The errors can add up.

Let's assume with a step size of 1MHz at the most max. 50ppm (error even when summed)
is too small even for the largest 1MHz step, comparing to +/- 0.5Mhz drift.


Manu




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