hi all;

     if the LNB LO frequency is not match with the LO frequency from the decoder, does it receive any signal from the antenna?

Provided DC power to the LNB is ON, the LNB will receive satellite downlink signals and send them via the L band cable to the receiver.  The frequency of the signals in the cable will differ from the satellite downlink frequencies by the local oscillator ( LO ) frequency of the LNB.  

If the software inside the receiver includes the LNB LO frequency then the actual LNB LO freq must match the corresponding LNB LO frequency set in the receiver software.   The two figures must match if the receiver is to correctly calculate the L band tuning frequency.   Such software expects inputs of the actual satellite downlink carrier frequencies like 11.123 GHz.      

In the case of very simple receivers programmed in L band frequencies, the LO frequency of the LNB and satellite carrier frequency are matters for your own external calculation.  Work out the L band frequency required yourself and input that directly to the receiver.

Best regards, Eric.

  why they (astro) want to change their LO frequency from 10.00GHz to 9.75GHz? any specific reason for that?

Receivers typically accept L band signals in a range starting at 950 MHz.   If you want to receive satellite signals starting at 10.7 GHz then you need a LNB LO of 9.75 GHz.  Maybe Astro are starting some services in the band 10.7 - 10.95 GHz ?

For satellite TV, 'universal' LNBs with switchable LO frequencies of 9.75 and 10.6 GHz seem to be common.

For Ku band reception, LO frequencies of 10, 10.75 and 11.3 GHz are also available.

Best regards, Eric.

       where to get the quotation for this kind of LNB (without feedhorn)? i had surfed the net, but is still hardly to get this kind of LNB, most of them is LNBF... any others recommended site for that? thanks...

regards:-

Voon

Some examples:
https://www.invacom.com/
https://www.sepatriot.com/
https://www.smw.se/

Best regards, Eric.