amsat down converter v3d

  • Hello to the group,

    I plan to use the two types ( OCXO /GPS) of Amsat downconverters to listen to the NB transponder in a first step ;

    for this, the LNB signal is injected in the upper left F connector and the 144 Mhz signal comes from the upper right bnc connector.

    The jumpers voltage are in position 'by default' and the 4 leds on the right side of the pcb are illuminated except the 3rd one (green) which is blinking.

    The output frequency selection is on 6 which corresponds to 144.550 Mhz.There is hiss but no audio.

    What am i doing wrong ?



    renauld on4kvi

  • Ok Renauld,

    I have a similar problem here.

    If I use a short cable it works fine. If I try to work over the long distance to the dish, it did not work.

    If I use the LNB without the amsat downconverter it works well.

    Maybe a LNB 14/18V power problem....

    73´s de Robert

  • i use a lnb with an internal clock modified by tcxo ;

    the previous amsat downconverter works like a charm !

    It should work well too...

    I'm not sure if you have the jumper's right.. LED's definitely look good.. all on and the green one blinking...

    What is your TCXO frequency in the LNB?

    You might also wwant to look here , but it's mainly in germnan:  AMSAT-DL Sende- und Empfangsmischer für QO-100 (P4-A)

    Peter Gülzow | DB2OS | AMSAT-DL member since 1983 | JO42VG

  • Hi Renauld,

    Running the Downconverter V3d with an unmodified LNB may cause an unspecified frequency shift, maybe out of band.

    For the calculation of the output frequency (6 ... 144,55 MHz) the converter needs to "know" the LNB frequency, which is not the case if you don't use the clock delivered from the downconverter.

    By default the downconverter operates with 24 MHz clock. Your LNB may work with a 25 MHz TCXO, so you need to jumper the downconverter to 25 MHz by putting one jumper as shown in the documentation. Then you should get a signal on 144,55 MHz, but with some shift caused by the different frequencies of your TCXO and the downconverter's clock.

    If that works you should consider to modify the LNB to get a more precise output frequency.

    vy 73, Kurt, DJ0ABR

  • Tried here again, with a cable length of 45m the 24MHz level no longer seems to be sufficient for the PLL. I see the noise from the LNB but no signal. No problem with 16dB attenuator between LNB and converter.

  • DD4YR

    Hi Robert,

    Extracted from the Amsat Converter Doc : "Attention: The reference clock is only applied to the WB-LNB connection."

    So I do not understand further more....

    So do we need to have the NB AND WB together connected to the LNB ? I was using only the NB part.


    renauld on4kvi

  • Hello Renauld,


    If you want to use only the NB, you have to connect the LNB to the WB input, and connect WB output to NB input.

    I´ve done so and it works.

    73´s de Robert, DD4YR

  • Now changed to another dish (1,2m PF) with POTY, Koax lenght abt. 16m, connecoted like the pic above als Single LNB used.

    All works well.

    Frequency offset in the NB about 1.2 kHz.

    Is there a way to correct that?

    73´s de Robert, DD4YR

  • I think there is a complete misunderstanding of the concept of the new V3d Down-converter.

    The above wiring is only needed when you have a Single-LNB which is modified for external Reference-Clock provided by the V3d-DownConverter!

    For this the XTAL in the LNB has to be removed and *no* TCXO installed in the LNB.. Just a few components to inject the reference prided on the WB-In of the AMSAT Converter. It is not possible to feed the Referenc-Clock to an unmodified LNB .

    If you want to use an LNB which was already modified with adding a TCXO in the LNB, the above is senseless. In that case you can continue to use the NB-IN, but use the correct Jumper 10 A/B settings..

    If you want to take advantage of all functions of the new DownConverter V3d, you should modify a Twin-LNB as described here.

    Peter Gülzow | DB2OS | AMSAT-DL member since 1983 | JO42VG

  • I have some questions about my amsat DL downconverter v3.

    I use the one with the GPS reciever.

    When I connect the downconvertor to my modified LNB and my reciever I still hear some drift in the RX of the satelite.

    I have connect the LCD display to the downconvertor to check if the GPS is locked.

    When the GPS is locked there is still drift on the RX side.

    When you touch te PCB or the onboard TXCO you see and hear a massive freq change.

    How is this possible when the GPS is locked.

    It looks like the GPS reference / lock does nothing to the LNB reference signal.

    Is this right ?

  • No, the LNB reference is linked to the GPS signal.

    Is the converter in a housing?

    The TCXO is delicate and needs to be protected from draft.

    For experimental i have done it this way:

    Für ungeduldige,

    bei denen es die Konverterplatine während dem experimentieren noch nicht ins endgültige Gehäuse geschafft hat:

    Ein Stück leichter Schaumstoff mit Tape auf dem TCXO fixiert bewirkt Wunder was die Frequenzstabilität betrifft!

    73´s de Robert


    Robert - DD4YR - JN57QS

  • @PA1PAS: the GPS reference frequency goes through an extremely slow PLL ( a couple of seconds). This is required because the GPS module output has a very precise frequency, but has a huge jitter.

    The PLL is too slow to compensate a short term drift caused by a temperature change of the TCXOs.

    A good enclosure helps to solve that, and additionally Robert's hint to put a piece of foam over the TCXOs also helps a lot.

    All frequencies, including the LNB reference are derived from this PLL.

    73, Kurt