Just asking!

  • I have been using a cheap TRIAX single LNB to date, it's got a PLL oscillator but can still drift quite a lot.

    As I had a spare I thought I would have a look inside. The unit seems to use a small surface mount TXCO of some description, the only way I could see some of the details is by taking a picture.

    As it uses one of these oscillator blocks, I think it could be easy to modify by bringing a small cable through the lid!

    I read a few conversions from crystals to external and discussions about driving single or double ended etc.

    I think I have marked the osc correctly, does anyone have a data sheet on the 3566E

    It may not be the best idea but something I think I will have a play with.


  • Hi Dave I thought for a second you were pointing me to a 3566E spec sheet. I hope to use a OCXO I have for the job, and put it all out side in a box at some time as I slowly improve the set-up, receiving SR33K and SR66K video can be fun when the LNB can drift more then that. But it also should add some stability to RX for narrow band as well. Thanks for the link.

  • Hi Adrian !

    The photo you postet does not show a TCXO.

    It's just a simple x-tal, nothing more.

    If you follow the striplines you see the typical x-tal design with the 2 ballast Cs.

    And the x-tal case is just connected on 2 pads.


    Armin DF1QE

  • DF1QE Good morning and thank-you, you are of course correct. I made the assumption it was a 4 pin TXCO as the bottom left pin is at ground and it matched a data sheet. Checking this morning with power applied there there is no VCC to the chip, so I bow to your better understanding of these LNB's. If it is a typical inverter input stage on the chip anyone know which is input and which is output or is it a case of play and see? All the images I have seen do not seem to be the same 3556E.

    A new day starts.


  • Remove the capacitors on pins 6 and 7 and inject via a capacitor into pin 7 i/p, check with a very good scope and 10:1 probe that your signal is coming out of the o/p pin 6.

    The board runs of a 6V regulator so you may have to reduce the voltage to your TCXO. I did this with a simple resistor and 100n decoupling capacitor.

    You do need of course good skills and experience in this.

    Dave Cawley | Ex G8EAO & G6ANG/T |
    (when you had to have a separate TV license !)

  • Hi all.

    A lot is being written about modifying various LNBs :thumbup:

    But I have, maybe a stupid beginner question,

    about the practical use of the LNB.

    Since 2 months I have had a dual band patch feed

    ,with a TXCO modified Otagon LNB,

    and I wonder what is wisdom

    constantly provide the LNB with voltage

    or is not that special necessary

    I know that some commercial sat receivers keep the

    voltage on the LNB in standby mode and others don't?

    Does anyone have a tip in this ??

    Tnx Jan

  • Hi Jan,

    they are two different aspects. Some commercial satellite TV receivers leave the LNB always powered because even in standby mode they receive from the provider a new channel list, a new firmware etc. In any case, not for reasons of stability. A few kHz drift does not affect the reception of TV channels.

    For our use, leaving the LNB always powered is aimed at system stability. Yes, in our case it is certainly useful to leave the LNB always powered.

    Ciao, Lucio

  • Hi Lucio

    The reason for this question was that I still have to make a few minor modifications in the transverter housing.

    And whether I would also supply the LNB with voltage from the transverter power supply

    which is not always on.

    So I think it is indeed wise to supply the LNB with power separately, and leave it 24/7 on

    Thanks info
    Ciao, Jan

  • DD0KP Hi Heiner

    I read the article about this possibility but thank you for mentioning it.

    The power supply for feeding the LNB is no problem.

    I made a Bais-T with the possibility to switch between 12V and 18V and it works great.

    The original question was whether it would be wise to supply the LNB with voltage 24/7.

    Given the answer I leave it as it is and as long as the LNB continues to work.

    Attached some photos of the Bais-T i have made

    For the POTY in focus of the 1.2M dish see my avatar

    73's and tnx for reply


  • Hello Jan,

    I have a modified octagon on my dualband feed too, but never leave it powered on. No problems when powering on, in less then 2min all is stable here. Even in weekends, i just switch the power on for the complete station when i want to work the sat. Good luck and welcome to the transponder.

    73's, Jerry