Saturday, February 23, 2019

10GHz LNB with PLL and TCXO





   Satellite LNB is very cheap source of 10GHz converter. Especially now, when the classic DRO was replaced by the PLL with X-tal. I played with 10GHz tropo web SDR RX. It works great. There are two LNBs with one TCXO. You can see more here. As IF RX there is nice RTL-SDR toy. I do have TCXO for that as well and done some modification for better stability. You can find more here. 


   There are two (?) X-tal frequencies in the LNB. I do have one with 25MHz but I have seen one also with 27MHz.  LNB with the original X-tal can be 100kHz shifted. After heating it is stable, but not as well as with TCXO. There is standart X-tal so you need to use some SDR for the IF frequency. 

For example, the 25MHz is multiplied by 390 to 9750MHz. If you calc IF then it is:

10 368MHz - 9750MHz = 618MHz

For Es Hail 2 it is:

10 489MHz - 9750MHz = 739MHz

I ordered also another two TCXOs for 70cm IF. Than:

10 386MHz to 432MHz is 25,476923MHz
10 489MHz to 432MHz is 25,787179MHz

But I ordered 1ppm TCXO, so there is some mistake done by the production:

 
This is not a problem for SDR RX where you can do some calibration. But for classic 70cm RX you do have some frequency offset mistake :( 

Do not forger, any small mistake is multiplied by 390 !!! So 10Hz is finally 3,9kHz !

Almost right frequency
21Hz mistake means 8kHz on IF (RF)

Rebuilding the LNB. There is a lot of different LNBs... In my one I remove original X-tal and add TCXO. There is close V-stab what is and is not good. It is easy to connect power supply to TCXO on the other hand, this stabiliser produces heat... There are more ways, I used 1k8 resistor from 6V to TCXO. It is 3V3 one. Or you can use 3V3 zener diode and 680 ohm resistor. Do not forget to 100nF capacitor or more.

With zener diode

TCXO description

Voltage bias tee. There is a PCB designed to do voltage supply bias to LNB over the coax, with some protections and also variable ATT. LNB + RTL-SDR can have too high gain, so you can set it as high as you need!




 I can offer you TCXO, rebuilded LNB and bias tee. If you are interested, please contact me at:

honza at ok2zaw . com


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