Down Converter V3d defect?

  • Hi,

    I've used the Down Converter V3d with the GPS-Modul V2 for several month now. It worked as expected.
    Today I got a problem. It seems that the some PLL isn't locked and some frequency isn't stable. You can see the effect on the screenshot. All Leds are ok and also the seriell Debug output from the converter looks normal.



    Does anyone knows this effect and maybe have some hint?


    For clarification:

    The TRX is Adalm-Pluto, external clocked with 40MHZ from the Down-Converter.

    The LNB is modified and also ext. clocked with 24MHz from Down-Converter.


    73, Hartmut

  • Hi,


    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.
    Cheers,
    Jonas

  • Hi,


    I asked Kurt DJ0ABR and he replied:



    "what Jonas writes sounds like the PLL on the GPS module is not locked.


    I've seen something like that myself when the GPS signal was weak, but after 2 seconds the PLL was locked again.


    What is also important to know, how many GPS SATs does he receive at all.


    Most people don't know this because they don't have a display, but this information is also available on the serial port."



    I it doesn't help, please send an eMail to our office...


    73s Peter

  • Hi,

    I had erratic and unexpected readings on my counter just as you had.

    Get a Display like this: https://www.az-delivery.de/col…/1-3zoll-i2c-oled-display ,

    hook it to your Downconverter via a 4-wire connection. Amongst other Info, it will show how many satellites you receive, so you can tell THAT is or is not the cause for the trouble. I used the V3D for a while and noticed (in my qth) gps-reception is weak or completely fails now and then. I would never know if the unit was in a box where you can't watch the LEDs. OTOH a box is important because every small airflow causes the TCXO to drift and makes the correction do it's job. You can see that as drift on the downlink.


    73s , Martin

  • 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, https://amsat-dl.org/der-neue-…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?

    Cheers
    Jonas

  • Hi,

    i sold my V3D some time ago, so I can't duplicate your tests. In any case, the LNB - connected or not - does not affect the reading / display. IIRC "Sysclock wait" implies V3D is not fully up yet. Maybe you have trouble with the satellites. Reposition your GPS-Antenna might help? You do have a gps-antenna, do you?

    ****EDIT*****

    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...


    Your screen should look like this:

  • 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.


    ****EDIT*****

    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...


    ****EDIT*****

    Sorry, I understand now.

    I found what you mean:
    https://amsat-dl.org/en/der-neue-amsat-dl-qo-100-downconverter-v3d/ 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?

  • Hi,

    Reposition your antenna. According to Fig 8. , check if the gps-module is aligned with the pins and that there are no solder bridges shorting Pin 3 and 4. Can you verify the voltage on Pin 1? If everything is good but V3D still won't load further than to the point where it's stuck now, , i think it's time to ask amsat-dl for advice what to check. As a last resort you might return V3D to amsat for repair.

  • Hi,

    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.

  • 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?

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

    I think so. Did you reposition your GPS antenna? Where is your antenna located? Indoors? Can you try a different GPS antenna? At my qth, if i put the antenna behind the window and shutter, gps-reception now and then drops to zero. If i put the antenna outside just on the other side of the window and shutter i have 7 satellites minimum.

    In my version of the Down Converter this signal has to be provided by an external source, right?

    Yes. I'm not sure about the level. Remove the GPS Module , put a jumper across 3 & 4, feed 10MHz to 5. The frequency schould be extremely accurate, because it will be multiplied to provide 24 (25) MHz and the LNB will multiply it factor 390 for 9360 (9750) MHz, so even a small deviation will result in an offset. BTW, your LNB multiplies by 390, right? If the multiplier is different, we need to recalculate.

    Please name the brand and model of your lnb.

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

    You might, but what for? You can check for 10MHz while it is built in, no need to pull it out.

    You said you successfully use an unmodified lnb. So the dish is pointing to the sat. One error eliminated. But: 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.

  • 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!

    Jonas

  • GPS Antenna: Any that can handle the voltage from V3D should do, there are many available ranging from just below 3 V to just above 5V.

    Modified lnb: Is it known to work properly (like give it to someone to test in a different setup) , do you have access to a 24(25)MHz source? Do you have a frequency counter or shortwave receiver to verify 10MHz at the 10MHz output, 40MHz respectively and 24MHz at the WB-connector of V3D (careful, there is 18V , pull the jumper before that). Do not measure at the gps-module, measure at the dedicated outputs. IIRC you can use V3D witht the gps removed , you then should also find those frequencies, just maybe a little offset. I'm still convinced that you loose the gps-satellites. BTW, it takes a couple of minutes for V3D to provide all outputs after it was powered up and has gps signals.

    Can you transmit with a handheld on 437.075MHz in front of the lnb to see the 24th harmonic on 10490,400?

    How did you receive 739 MHz on gqrx? What was the setup? Was it different from the setup when you received on 144MHz? Just the lnb or did you exchange more components? Is there a short in the plastic bnc output->144MHz? When you use the unmodified lnb instead of the modified one, does the combo lnb -> V3D -> sdr(pluto?? or what?) ->gqrx work?

  • Modified lnb: Is it known to work properly (like give it to someone to test in a different setup) , do you have access to a 24(25)MHz source?

    I cannot say if it is working properly. Unfortunately I also don't have anyone to give it to. But I have an oscilloscope at hand which can provide up to 25 MHz output.


    Do you have a frequency counter or shortwave receiver to verify 10MHz at the 10MHz output, 40MHz respectively and 24MHz at the WB-connector of V3D (careful, there is 18V , pull the jumper before that). Do not measure at the gps-module, measure at the dedicated outputs.

    I have measured those outputs today with the oscilloscope. I removed the GPS, out the jumper on PIn 3 and 4 and fed 10 MHz into Pin 5.

    (Green signal, yellow ground)

    Nevertheless tho whole time the display showed me the "Syslock : wait" screen. The dedicated outputs on the other hand were fine, except for some minor deviations. The 40 MHz was like 40.2 and the WB ref. was around 25. Though I had both jumpers (10A and 10B) removed and it should have been 24 I think.


    Then I tested the Down Converter set up with the unmodified LNB. As you showed in the picture I removed jumper 14A set 14B correctly, connected NB in to WB out and the WB in to the unmod. LNB. But still I wasn't able to get any proper reading. I think mainly because the Down Converter is still in the Syslock Wait state. For what ever reason.


    IIRC you can use V3D witht the gps removed , you then should also find those frequencies, just maybe a little offset. I'm still convinced that you loose the gps-satellites. BTW, it takes a couple of minutes for V3D to provide all outputs after it was powered up and has gps signals.

    You mean remove the GPS just like that and don't feed an external reference signal?

    Yes I have been waiting patiently for the out puts and the GPS.



    Can you transmit with a handheld on 437.075MHz in front of the lnb to see the 24th harmonic on 10490,400?

    Which LNB do you mean the modified?

    The only handheld i have Is my Phone (Ulefone armor 3WT) I don't really know if its sufficient. I guess I could also get my hands on a second Pluto SDR if that's better.


    How did you receive 739 MHz on gqrx? What was the setup? Was it different from the setup when you received on 144MHz? Just the lnb or did you exchange more components? Is there a short in the plastic bnc output->144MHz? When you use the unmodified lnb instead of the modified one, does the combo lnb -> V3D -> sdr(pluto?? or what?) ->gqrx work?

    I received the 739 MHz with the set up:
    unmod. LNB -> bias tee -> Pluto


    The 144 MHz is supposed to be the output frequency of the Down Converter in the set up:

    mod. LNB -> Down Converter -> Pluto


    For now i have only tested the unmod. LNB with the external reference from the osci which didn't work. I will test it with GPS and if possible without both. Do you have any Idea why I get syslock wait and I could fix it?


    Cheers
    Jonas

  • Alright, it seems you are not a ham-radio operator, otherwise you'd knew what a handheld or walkie talkie is.

    So you can not transmit on 437MHz to check the lnb.

    Ok, 40ish MHz an 25ish MHz is good! Means the TCXO in V3D is working and you have output, just not disciplined by GPS.

    Now, who modified the LNB? Was it someone who can check it ?


    Feeding the UNMODIFIED lnb with 24(25) MHz external will not work. It will use it's internal crystal.

    But you should see signals on 144MHz IF YOU jumper V3D to 25MHz and listen on 144MHz. The output of the unmod lnb is 739 MHz and will be converted to 144MHz if V3D is set to 25MHz , otherwise , when it is set for 24MHz it expects 1129MHz to convert it to 144MHz, so if you still feed in 739MHz, the output WILL NOT BE 144MHz. Here's why: Modern lnb's use a 25MHz crystal, multiply the frequency by 390 to get 9750MHz . 10490MHz-9750=740MHz . In order to receive the Amateur TV-Transponder with consumer electronics satellite receivers, which cannot receive 740MHz, one must use a frequency they can handle. So if you feed 24MHz instead of 25, the result is 10490-9360 = 1130MHz, which they can handle. So i think you are close to receiving with your unmodified lnb->V3D->Pluto on 144MHz if you set V3D to 25MHz. Try it. Just don't bridge NB IN and WB out, but hook the unmod lnb to NB IN. If that works, the culprit might be the modified lnb. So once you have a working modified lnb, next step is to find out why gps doesn't work.

  • A few more hints: A unmodified lnb may be far off. So set your gqrx bandwith 2MHz wide , just to be sure to find the satellite. The lower telegraphy-beacon should be on 739.5 , the upper beacon about 500kHz higher. Right in the middle between them, there is the psk-beacon. While you receive the satellite, you might want to reposition your dish for optimum signal-to-noise ratio. Don't forget the skew angle, it should be about 13 degrees.