Looking for a dual (or more) output LNB lockable to 25MHz up the coax??

  • I am wondering if you know where I can get, a dual output LNB ready to be locked to 25MHz up the coax? I have a single output LNB from QRO.CZ that works very well with their special Bias-T box and a 10MHz reference that I already have, down the coax? I want to be able to receive horizontal and vertical signals (SSB and DATV QO-100) at the same time, on the one PF 1.8 metre dish.


    If nothing is commercially available, what is currently available that might be modified to enable this please, with some published, clear instructions?


    Thanks and all the best from England. Chris, 2E0ILY

  • I think most LNBs that have a crystal should be lockable to an external ref. http://www.pabr.org/radio/lnblineup/lnblineup.en.html#
    As of now, I have successfully injected a 25M reference into the 3566 marked chip found in many chinese LNBs, and also the RT320M, which is a twin LNB chip. I am pretty sure it can be implemented in quad LNB chips aswell.

    It is just a matter of removing the crystal, and injecting your reference with a simple diplexer (LC series and LC parallel) into one of the crystal pads, just like this http://www.hybridpretender.nl/single.pdf


    Also, something that is not covered in that document, and I had problems with, is cutting the wiggly line going to the voltage regulators and adding an SMD inductor. That wiggle line is enough inductance to block the IF going into the regulators, but is not enough to block a 25M signal, and the decoupling caps at the input of the regulator were eating all of my 25M reference preventing the LNB from locking. Once I added an external inductor (820 nH IIRC) it locked just fine.


    Attached is a picture of a cheap 3566 single LNB where I did the mods. Sadly i did not take pictures of the RT320M LNB I modded.

  • Thanks SWL-jsilva, appreciated.


    I have managed to find an Octagon quad outlet LNB that appears, as far as I can tell, to be the same as the one on a clear internet site. It shows how to modify it with photos. It's in Greece though and shipping is more than the cost of the LNB itself, but hey, you can't take it with you I guess [Blocked Image: https://forum.batc.org.uk/images/smilies/icon_e_smile.gif] I will open it with some trepidation when it eventually arrives, hoping in reality it IS the same. This is all probably easy to the more experienced here, but the first time is always the most worrisome :)


    Regards, Chris 2E0ILY

  • Also, something that is not covered in that document, and I had problems with, is cutting the wiggly line going to the voltage regulators and adding an SMD inductor. That wiggle line is enough inductance to block the IF going into the regulators, but is not enough to block a 25M signal, and the decoupling caps at the input of the regulator were eating all of my 25M reference preventing the LNB from locking. Once I added an external inductor (820 nH IIRC) it locked just fine.

    The proper way, IMHO, is to make a parallel resonance circuit on 25 MHz. That will keep the reference where it is supposed to be.
    Personally I use 150nH and 270pF. Note that with SMD these can be "stacked" making it easier to find space for them.

  • The proper way, IMHO, is to make a parallel resonance circuit on 25 MHz. That will keep the reference where it is supposed to be.
    Personally I use 150nH and 270pF. Note that with SMD these can be "stacked" making it easier to find space for them.

    Hm, yea, I get your idea, basically the same we are doing to prevent the 25 MHz from leaking into the IF path, but instead to keep it out of the DC path. Didn't think of that, I just figured a big inductor will work like in a bias T.
    Next time I mod an LNB I will try an LC tank instead of just an inductor and see if the results are better. Thanks.

  • Without wanting to play my own harp, see https://forum.amsat-dl.org/index.php?thread/2856-transverter-pe1cmo-and-kuhne-down-konverter/&postID=9489#post9489


    I don't know if Megasat has a good representation in the UK, the BRexit has caused a deep ditch to the mainland but let's keep the forum technical please!


    However, brand and type doesn't matter that much. Keep in mind that if you buy a certain type of LNB, and you order the same type 3 months later, you will likely find completely different electronics inside. In that regard, what does matter is to "buy a few at once". If you break one, you have learned the construction and the next one will be easier to modify\; you also have "one to look at" which I find, helps a lot.


    The key is to get a LNB with crystal reference. The good news is that these are cheaper than older models with DRO. My suggestion is you buy a few, open one, if it is a DRO-type, send the other ones back unopened. Personally I find it difficult to ind DRO LNB's these days; PLL is much more common

  • Thanks SWL-jsilva, appreciated.


    I have managed to find an Octagon quad outlet LNB that appears, as far as I can tell, to be the same as the one on a clear internet site. It shows how to modify it with photos. It's in Greece though and shipping is more than the cost of the LNB itself, but hey, you can't take it with you I guess [Blocked Image: https://forum.batc.org.uk/images/smilies/icon_e_smile.gif] I will open it with some trepidation when it eventually arrives, hoping in reality it IS the same. This is all probably easy to the more experienced here, but the first time is always the most worrisome :)


    Regards, Chris 2E0ILY

    No problem.

    When I did my first mod, it was on a single LNB, and I also screwed it up. Mainly because the metal case had little room for my big SMD components (0603), and when I closed it was shorting something out. It is okay tho, I always order more than one, preferably 3, as people say: one to replace the first one that I screw up, and other to spare. I can get them locally for about 3 euro (the single LNB version), so it was not a problem for me. Good luck !