Any information about these Megasat QUAD LNB's?

  • I am using the model from your second link, the same but the twin version. I have also the quad version here and will modify it this week.

    It is a PLL model using a 25 MHz crystal. It has the usual drift like all models have, but it is very easy to connect an external signal source, in my case a leobodnar GPS which works excellent.

    The other link pointing to the multifeed looks to be DRO.

    If you have access to the cqDL 1/19, there is an article about this Megaset LNB and its modification.

    73 de Kurt

  • I have opened and modified the Megasat Quad-LNB (see PH2M's link above) to connect an external reference (25 MHz):

    This is the original LNB:

    first the black plastic cover was removed, then it looks like that:

    Now I removed the silicone:

    and removed five screws (Torx No.8):

    the 25 MHz Crystal is at the right. What a funny layout, the traces from the crystal go over half of the board to the chip, but it works so its fine.

    The external 25 MHz must be fed into pin14 of the chip. It did not unsolder the crystal (which is very hard to do), instead I cut the trace close to the chip:

    the wire of the connector was desoldered from the board, and via a 1nF capacitor a thin wire goes to pin 14 of the chip.

    The connector is now marked "LO". This is where I connect the output of the leobodnar GPS. Via a simple 25 MHz low pass LC PI-filter, 2x 220pF and 680nH in series). This filter reduces the level to abt. 6dBm.

    Three LNB outputs are available. I am using one for NB and another for the WB transponder.

    vy 73, Kurt

  • PH2M , i know the circuit in your link. It looks good except one thing.

    What looks strange: L4 ... 10uH.

    These SMD parts (with 10uH) have self resonance frequencies of usually below 100 MHz. So it will be just a capacitor at 739 MHz and pull down the LNB's output signal through C5.

    And L5 with 10nH has no effect.

    I think L4, L5, C5, C6 should be recalculated.

  • I think you are correct, the values are different in the final article in the

    BATC CQ-TV 263, maybe Mike G0MJW could give some comments?

    I 'am still awaiting the BATC PCB and have to reorder some components also because of the different schematic component values :/

    73 de Frank PH2M

  • I drew a circuit diagram at our radioclub (where we have pencils and no sharpeners ; -) when somebody asked me how I do it. See picture below.

    Use Thomson's formula for f = 25 MHz and fit the components to what you have in the junkbox.

  • This was all about getting DC in without getting 750 MHz and 25 MHz out. It is supposed to be a low pass filter. The 220nH is blocking the IF, The 10uH the reference. They may have been the wrong way round in an earlier diagram but they are OK in CQTV. It was supposed to be published last year but got bumped.

    Well, that's what it is supposed to do but if you know better please do it.