AMSAT-DL Downconverter LNB Reference level

  • I wonder what the level of the LNB reference (24/25MHz) of the Downconverter should be and whether it can be adjusted?


    I have got the Downconverter and the modified Opticum LNB from Amsat-DL. I was never 100% happy with the receive performance though. Compared with an unmodified Opticum LTP-02H, the SNR according to SDR-Console is 6-7dB less and I can't see transponder noise using a 90cm dish.

    I now also have got the DXpatrol RX set with their LNB and Reference-Injection. Using that combination, I am also getting 6-7dB better SNR.

    I don't need WB RX at the moment, so I disabled the LNB Bias on the WB output and connected the DXpatrol LNB. Again, I am getting better SNR (not quite as much) but also many mix products. I guess that is due to too high reference level.

    Hence my question at the top about the reference levels. Also, any idea what (if anything) might be wrong with my AMSAT-DL LNB.

    Many thanks, 73

    Carsten G0SYP/DL1EFD

  • Did you connect like this? Please check for shorts (Kurzschluss) you might have introduced when soldering the F-sockets.

    I no longer have the amsat-downconverter, but the SNR was as good as with any other setup i used later. So if your SNR is not what it should be, (/and you connected everything right) there is definetely something kaput.

    If you have a lnb with 2 ports, WB should carry 18V and 24/25MHz , NB should carry 14V.

    73, Martin

    Edit: I can't download the circuit diagram from the amsat wiki, i only get the first and last page, all others in between are blank.

    But i have a copy of this on my HD, so if you experience the same, just ask . I will send you a copy. OTOH, there are no levels shown .

  • No, when connected to the Downconverter, I connected both the NB and WB to the LNBs. I removed the jumper on 14B so that no supply voltage is on the WB port. This works for both the Amsat and the DXpatrol LNB.

    There shouldn't be a short - I can measure both supply voltages at the LNB side of the coax (if the 14B jumper is in).

    On the wiki there is a level for the 10MHz (0dBm@50Ohm) and 40MHz (3Vpp) references but not for the 25MHz.

    What I haven't yet tried is the Amsat LNB with the DXpatrol reference (supposed to be 2Vpp).