Transverter PE1CMO and KUHNE Down-Konverter

  • I couldn't use the original 5V LNB from PE1CMO with my Transverter.

    I have modified a number of "twin LNB's" - using one port with PE1CMO modification (25 MHz reference via coax, low-noise 5V power supply), and keeping the other LNB port original.

    This 2nd port works with a regular TV receiver, probably with a touner - and if you put 18V on that port, that port will switch polarisation for the wideband transponder and the CMO port remains the same.

    The 2nd port obviously will only work if the CMO transverter is switched on since the 25 MHz reference comes from there.

    I put an adapter F->BNC on the CMO-modified port to prevent me plugging in a normal tuner on that port - the 13/18V on the modified port would instantly kill the LNB.

    And the 2nd port is rock stable as well since it uses the same reference - connecting a SDR receiver only measures the drift of the SDR dongle, and connecting a TV receiver I was able to receive Palestine TV which is on one of the transponders on BADR4 which is is on the same position.

    It switches polarisation with 13/18V and switches LO, for that port only, if 22kHz is sent, as is common with "universal LNB's".

    I can even use this modified twin LNB with a POTY.

    My personal favorite with this is the Megasat Diavolo Twin. Very good reception this way.

  • Thanks - this is a very elegant soution with a twin-LNB. Where can I buy such a twin LNB where is one port modofied to use the PE1CMO Transverter?

    73 de HB9RYZ


  • TWhere can I buy such a twin LNB where is one port modified to use the PE1CMO Transverter?

    Let me try to show a few things. "Modifying an LNB" has been covered on this forum and elsewhere, but I'm adding a few details that are hopefully useful. Most of these things I didn't invent, just standing on the shoulders of others, but the modifications I do I have not seen published yet.

    Modifying an LNB sometimes goes wrong, and I have a few LNB's that served their purpose as me getting experience, but that I ruined in the process. I found that if I'd order through aliexpress again, the types of the next shipment would be different, or the type I want no longer available, e.g. starcom sra-3602 ACE is now replaced by sra-3602mini, which is a very different beast (and which I find is not as sensitive).

    To avoid that, and to avoid waiting for aliexpress for replacements, I bought some LNB's at Reichelt, prices higher but worth it, certainly because I can also order the SMD's and other kit I need for the mods at the same time.
    I have found the Megasat Diavolo Twin and Megasat HD-profi Twin to be more stable and less noisy even without modification, so that's what I describe here.

    Note that especially the Diavolo has been described by others (even in funkamateur magazine) but my mods are slightly different.

    When you order, my advice is to at least order one more LNB than the number you want to modify so you can have an accident with one.

    The PE1CMO transverter does a few things slightly different. It injects a low-noise 25/27 MHz reference on the one LNB cable (so no separate cable - power supply, reference and IF out all over one cable), but it feeds the LNB with a low-noise 5V power supply. For twin LNB, this adds a few issues you should be aware of.

    A Twin LNB is a slightly different beast. The two receivers usually share one crystal, so both receivers should be powered up for one of them to function, and while a single LNB has a 5V stabilizer, twin LNB's have a 6V stabilizer (one for each port) and the output is combined with diodes (6V is to overcome the 0.7V threshold of the diodes).
    Feeding such a beast from 5V is a problem because you cannot use the diode. However, since the LNB can only function if it receives its 25MHz reference signal, I decided to unconditionally power from the 5V CMO port and not use the other port to power the LNB.

    Another issue is that a LNB uses the input voltage on its port to sense what it should do: 13/18V for polarisation, 22kHz to switch LO frequency, and if there is no voltage on the port (remember that the LNB can be fed from the other port!), switch off the IF output. This switching is arranged through a voltage divider from the IF port of the LNB. Feeding the LNB from 5V may switch off the LNB IF output because the LNB thinks the port is not powered. So you need to arrange for that.

    Opening the plastic case has been described before; it takes some experience (and one or more ruined LNB's ) to know where the plastic latches are and how to avoid breaking them. It is a matter of squeezing the half of the casing that has the latches and poking a bit with a screwdriver.

    The case is closed with Torx T8 screws and white putty. I have best results if I cut through the white putty along the seams, and along each screw. If you then stick in a Torx screwdriver the screws loosen easily. Once all screws are removed, lifting the top is easy, gently stick a knife or screwdriver in the seam and jimmy open, being careful not to disturb the inner electronics.

    The hi-Q then looks like this (sorry for the bad photos, spent one evening and two LNB's to make this posting!


    I decided to make the bottom port for the CMO-transverter. I removed the following components:

    • Lower 78L06 stabilizer + capacitor between middle and right pin (== input). Also remove capacitor at end of PCB coil (left of coil, to ground)
    • Crystal (square next to the screw in the middle of the PCB, inbetween the 2 RF chips), and both capacitors
    • Diodes combining the outputs of the stabilizers (both ports, two diodes)
    • Resistor and bypass capacitor of port sensing voltage divider (under lower RF chip)

    A few words on removing components. I used a heat gun and even then I found that these components won't let go. The reason is that the PCB is held in the metal casing and trying to heat up a component only heats the casing.

    Because of that, the procedure is:

    • De-solder the connectors of the two IF ports. Whatever you do, DO NOT PUT PRESSURE ON THE TRACES - especially when heated they loose very easily. My advice is to use desolder braid to remove the tin, then gently lift the pin of the F connector, but only to verify that the pin is no longer mechanically connected to the PCB
    • Remove the screw
    • Lift the PCB (take ESD measures!), put PCB on top of the IF pins
    • Now lifting the components with hot air (pyropen) is simple.
    • After lifting the pins, wet pads with fresh solder and clean pad with desolder braid. You will appreciate this for the next steps
    • After all components are removed and the PCB has been cleaned, re-install and put screw back so that board is mechanically stable.

    After the components have been removed, the steps are:

    1. Solder capacitor 270pF (size 1208) over the outer pins (input and output) of the stabilizer you removed.
    2. Solder inductor 150nH (size 0806) on top of capacitor of step 1. After this, you can check continuity between IF poort pad and the anode pad of the diode you removed
    3. Bridge the lower diode (the one from the CMO port). The other diode doesn't get replaced.
    4. In place of the resistor/capacitor of the voltage divider, solder new resistor (original value: 56k, new value: 16k, size 0402). I used 15k instead of 16k, it's not critical.
    5. Solder IF F connector pin back to pad, then solder series circuit of 270pf (size 0806) and 150nH (size 0806) from IF connector pad. Other end of series circuit to short wire to top right xtal pad (oscillator input).
      (apologies to Remco, I didn't use an inductor coupler for real estate issues)

    The resulting mod then looks like this:

    After this, I put a F->BNC connector on the F connector of the CMO port, mark the CMO-port with a marker and secure the BNC connector with schrink tube. This is to avoid connecting that port to a regular receiver (13/18V) which would be the instant death of the LNB.

    After this, test (with casing closed and screwed tight, LNB won't work w/o top lid on!), and if both ports work, re-install plastic outer casing.

    Should you decide to drill a hole in the front of the LNB (see PE1CKK's website), make sure you measure and mark the hole you will be drilling, I found that it is quite easy to get the hole off-center.

    After this, the 2nd port (F-connector) "just works" as a LNB port, but the 1st port (CMO port) MUST be powered and have reference signal.

    I'll share Diavolo pictures in a next posting.

  • I'll share Diavolo pictures in a next posting.

    Here are the same pictures for the Diavolo.


    Components to remove:

    The resistor from the voltage divider had a value of 220k (I find that each type of LNB defines their own values). Replacement would be 73k or so, I only had 63k in stock (in 0402 size) but that value was OK still.

    After installing new components (no words on my soldering please!)

    If you wonder why the 25MHz series circuit is in such a strange place, look at the inside of the lid of the LNB.

    Comparing the Diavolo and the High-Q, I like the Diavolo better because it has less gain and the receiver is not as noisy. But perhaps each should decide on their own.

    When buying SMD's it makes sense to purchase a few spares; like fleas, if they jump off your pincer, they are gone forever, but they aren't expensive. And make sure you order solder braid at the same time.

    Again, many thanks to those who did the 'before me" but I didn't find all the info I posted here in other places. Good luck!

  • pe1hzg

    Thank you very much for your very detail post. I will go through your post and will decide after if I would gfo this route.

    Here is my current QO-100 Setup. The PE1CMO Transverter is used at the moment only for TX on 431 MHz.

    With thies soltution I'm able to work SSB and receive DATV with the MiniTiouner pro 2.

    The MER on the DATV Beacon is 7.2-7.3dB with my 1.25m dish.

    73 de HB9RYZ