Posts by SWL-Jonas

    Thanks for the plenty input!

    Did you reposition your GPS antenna? Where is your antenna located? Indoors? Can you try a different GPS antenna?

    Yes, I have re-positioned it. Originally it was inside directly behind the glass. I have put it outside and tilted it a bit. The signal seems to get more stable. But still not really reliable. Which is odd because I am at the top floor of the highest building in the area. I get between 4 and 7 satellites.
    Do you have any suggestions what GPS antenna would be a good choice?

    Please name the brand and model of your lnb.

    The unmodified LNB is a "LNB 1" digital single LNB by SCHWAIGER. Pretty standard with an LO of 9.75/10.6 GHz.

    How do you feed the reference from V3D to your modified lnb? The reference is on the wideband connector only, not on the NB-Connector. So if your lnb shares output and reference input on a single connector, you need to rethink the setup.

    I have two coax connections between mod. LNB and Down Converter. One for the NB and one for the WB+Reference.

    Had same effects with somtime GPS loss ... , mostly after new start of the converter.

    I changed the GPS Antenna, now without problem ...

    Maybe a try?

    73 de Robert

    Good Idea. May I ask which antenna you use?

    I promised you screenshots of the Gqrx:

    This is what I get with the bias tee and the unmodified LNB.

    This is the result when I use the modified LNB and the Down Converter. (Even when the display shows everything should be alright GPS wise.)

    I tried to measure the frequency on the GPS module but I wasn't getting anything that looked like a proper clock. I have to measure between GND (Pin 2) and Debug Output (Pin 4), right?

    I am not sure if I used the Oscilloscope correctly.

    I also made a very strange observation with the 40 MHz out put. When the display showed GPS running the frequency was not correct:

    But a few minutes later it was the other way round:

    Do you have any Idea what this could mean?

    Thank you very much for your patience!


    So if the display says "Syslock : wait" the GPS connection is lost?

    As for the dish I am very sure that the pointing is correct. I have a second unmodified LNB and a bias tee with which I am able to listen to the transmissions. I will get screenshots of the Gqrx when I'm back in the Lab.

    Also I was asking myself if I could test the GPS module and the Down Converter separately. You said if the GPS pins 3 and 4 are bridged the Down Converter uses a 10 MHz signal. In my version of the Down Converter this signal has to be provided by an external source, right?

    And for the GPS module: Could I power the module with 3.3 V and measure the frequency output at pin 4?


    Thanks for the quick reply!

    The GPS module seems fine, no shorting. I have checked the voltage its 3.3 V.
    I have experimented with the GPS antenna position. I am able to get enough satellites even though it takes some time, up to 5 min. But the display output is still making me wonder:

    First I get this: (don't get confused by the time on the display I took a loot of pictures the first ones didn't have sufficient quality)

    After quite a while it changes to:

    But as you can see in the background the PLL LED is still not on. Isn't it supposed to be on at this state?

    From then on it keeps changing back and forth to this:

    I have measured the external reference output and it provides a 40 MHz signal as it is to expect.

    However connecting the Pluto to the Down Converter output and reading the data with Gqrx I can't even see the beacons around 144.5 MHz.
    When I only connect the reference input to the Pluto and an antenna to the Rx I am able to get proper reading of the local radio stations.

    I am not sure what goes wrong here.

    I am a little confused now.

    Do you mean the pins 3 and 4 of the display connection providing the SCL (sometimes referred as SDK, Clock)?
    Or are you referring to other pins on the Down Converter? The only pins with jumpers on the Down Converter I know are the ones to define polarization and LO frequency of the LNB.


    I think i know whats going on!! Your display shows V3D is set to external 10MHz Reference Input! Remove Jumper on Pin 3 and 4. OTOH, how can you install a gps-rx AND the jumper? hm...


    Sorry, I understand now.

    I found what you mean: Figure 8, right?
    Those are the pins that the GPS module is plugged onto. Pins 3 and 4 are for the serial connection of the GPS and the debug output.
    The GPS module is occupying both pins so I assume there should be everything in order. But as you mentioned the display suggests that the Down Converter is expecting a 10 MHz external reference input. How can this happen?
    And more important how can it be fixed?

    Thank you for the Schematic it was very helpful.
    it seems the display works fine but I am not getting the detailed information about the GPS (like here in image 9,…qo-100-downconverter-v3d/). Instead I get a different screen.

    I tried the display without connection the DownConverter to the LNB beacuse its not at hand at the moment. Is that the reason for the different screen or can I manually switch the displayed information?



    I am relatively new to RF technology.

    For starters I have set up a small ground station to receive QO100. But now I experience very similar problems.
    In the beginning the DownConverter V3d (with GPS receiver) worked just fine. I am using a PlutoSDR and the modified LNB as well.
    For better signal stability I wanted to feed the 40 MHz clock reference from the DownConverter to the Pluto. So I modified the Pluto in order to connect the clock.
    Unfortunately the readings I am getting now are not what I expected at all. So I checked the Pluto without DownConverter. I connected the signal generator of an Osci to the clock input of the Pluto. Receiving the local radio stations with this set up worked nicely. To verify that the rest of the setup works correctly I built a simple Bias Tee. With the Bias Tee (antenna, Bias Tee, Pluto) I can receive the signals again.
    The DownConverter however is not working as it should. I have observed the following:

    1) GPS receiver LEDs:
    PLL: off
    Power: blinking
    GPS sat connection: on

    Though I have to say that I think i saw the PLL LED on for a second just after switching on the power for the DownConverter. But that was not reproducible a second time. I tried several times.

    2) DownConverter LEDs:
    Power supply(A): on
    Down mixer lock(B): off

    (C) : mostly off but blinks once in a while shortly
    Central PLL sync. (D): blinks

    3) I also measured several outputs of the DownConverter. Some measurements differed from the normal values.

    The 40 MHz clock output was giving 35.08 MHz or 48 MHz (varying from test to test).
    The frequency of the wide band output is 28 MHz instead of 25 MHz.

    The frequency at the GPS receiver 8.77 MHz instead of the expected 10 MHz.

    The Jumpers for LNB reference selection are at 25 MHz selection. (10 A bridged)

    Does anybody know the diagnosis for these symptoms?
    I am grateful for every hint to locate the error or further tests I could run.

    Thank you very much.