Wie QRV werden?

  • DD4YR said: "As Remco already suspected, the frequency stability for SSB operation is hardly sufficient, for digital operation not at all. When watching the beacon of Es'Hail in CW, the frequency is constantly drifting, moreover the sound is "jammering" in the loudspeaker. A quartz heater improves the frequency drift, but the jammering remains ....."

    Correct.


    I did these experiments about a year ago using a GPS locked signal generator on 10489.7 MHz listening to my 70cm transceiver. My primary design goal was 0.1 ppb (1Hz) stability (NOT accuracy) on 10 GHz.


    Listening to the tone on your receiver and dialing around/across the carrier is very 'educational' ; -)


    The carrier my be 'accurate' in time but may be a punishment to listen to because of 'jammering'. The carrier may be stable, but may be a punishment to listen to because of a 'hiss' or noisy sound in SSB/CW.


    Second VERY important issue is phase noise. I selected a VCXO (not having an NCO inside!) with very low phase noise, filter the output with a crystal filter to even further reduce the phase noise and locked it to a clean 10 MHz GPSDO. Of course the limit is the phase noise of the PLL LNB itself.


    Third (also very) important issue is noise on the power supplies. Here, all relevant circuits are powered through 'denoisers' (capacitance multipliers, being an emitter follower with a (large) capacitor from base to ground).
    One friend of mine got that far that he removed the 78L05 in his LNB (!)


    When I listen to the EB's 'in CW' with 500 Hz BW filter the tone sounds 'like a bird' with my headphones. I also checked it with the weaker parts of the EB's and the response is nominal.


    While writing this, I think about a following experiment:

    1. Inject a (GPS locked) carrier in my 70cm receiver and measure the audio response as function of signal strength (noise, distortion etc.)

    2. Repeat the same with the whole 10 GHz / LNB chain included.

  • Hello all,


    from my many experiments with different types of frequency stabilisation for NB SSB receiving i have the results:


    Best working solutions:

    -PLL LNB with software drift correction

    -PLL LNB with external reference (GPSDO)


    good working:

    -PLL LNB modified with "analog" TCXO (D75F) or OCXO


    barely working:

    -PLL LNB with "digital" TCXO


    not useable:

    -unmodified crystal PLL LNB without any additional mod or sw correction

    -DRO LNB without sw correction


    For DATV reception the results may be different.


    vy73 DB8TF

  • Hallo all...


    over the holiday time i spent some more time on my project ...

    SDR UPLINK TX .... with LIMESDR.


    (maybe possible also with ADALM PLUTO...needs mod with TCXO..pse give information about).


    For the test i use as SDR-TX the ODROID XU4Q and the LIMESDR-USB with an GNURADIO FLOWGRAPH. With this setup it is possible to TRANSMIT LIVE (delay around 0.5s) from an Mic connected on an USB soundcard (SB16).

    Some more testsignals (audio loop, cw loop,pskloop...) were generated in the GNURADIO FLOWGRAPH. Digital Modes are possible via virtual soundcards in pulseaudio direct on the system.

    The OS is Ubuntu Mate 18.04 armhf for Odroid XU4.

    Monitor receiver is on an other PC with the ADALM-PLUTO and GQRX. CPU load of the ODROID is shown right in the TOP of the VNC-window (Odroid XU4)


    Note:

    This is a first test an 2402MHZ and i used an DUMMYLOAD in the SHACK...!!


    the actual results can be seen in the video....



    BEST WISHES TO ALL for 2019

    73 de DG0OPK

  • Hallo Robert,

    parallel zum Satempfänger kann ich natürlich auch mein Winradio betreiben.

    Angedacht ist aber wegen der Laufzeit (könnte nerven) wirklich Simplexbetrieb.

    Warum nicht, wenn das gesamte System eine Frequenzgenauigkeit im einstelligen

    Hertzbereich hergibt und die Sendeleistung einmal ermittelt ist.

  • Interessanter Ansatz, ja. Bei geostationärem Orbit auch durchaus vorstellbar. Ich hab die Idee bisher noch nie erwogen und wegen Doppler und Antennennachführung ausschließlich im Duplex Betrieb gearbeitet...

    Bin ich ja gespannt inwieweit uplinkabhängige Leistungsregelungen im Transponderbetrieb ein Anpassen / Nachregeln der Sendeleistung notwendig oder überflüssig machen.

    Es wird sich zeigen.... :-)

    73s de Robert

  • Wir hatten die Diskussion an anderer Stelle schon einmal und Simplex-Betrieb ist generell auf Linear-Transpondern nicht statthaft.


    Siehe auch: Simplex operation


    Man sollte immer das eigene Signal beobachten und seine Sendeleistung ggf. anpassen und reduzieren.. auch würde man die schöne LEILA sonst nicht hören ;-)


    Mehr dazu:

    https://amsat-dl.org/p4-a-nb-t…-and-operating-guidelines


    OSCAR-40 war übrigens im Apogäum fast 60.000 km entfernt und an die Laufzeit hat man sich schnell gewöhnt.. hat das Ganze irgendwo auch interessant gemacht.

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

  • Hello,


    just a very trivial remark to save costs in becoming QRV via P4A.


    RF-specialists: please stop reading here. ;-)


    To save money for expencive 50 Ohm I use cheap 75Ohm Sat-coax not only for receive, but also for the connection of my 2m or 70cm TX with my upconverter. You just have to take a lenth of multiples of 1/2 lambda (keep in minde the shortening factor of your cable - if you don't know then just make try and error). And you should use very good shielded coax (like for reception also; e.g. 130dB four layer shield).

    Thus you have no transformation and 50 Ohm in and out. The signal loss is not significant.

    I have 20m to my antennas and an SWR of 1:1 with costs of less then 4 Euro (even RG58 is much more expensive).


    73 de Johannes


    P.s. some may think : Even my grandmother knew it

    My answer: But she didn't publish it :-)

  • In Amsat Shop is offered a Dual Feed. Question: what is needed in between Feed and Amsat "universeller Empfangsmischer....." ?

    Guess another Konverter in between ?

  • I am running now Wb and NB with one LNB with horizontal polarisation.

    Both signals are fine.. sat splitter into Mini-Tiuoner-Express and RTL-sdr..:thumbup:

  • DB8TF how do you connect the D75F to the LNB?


    Straight at the xtal input pin after removing the xtal, or do you need to adapt signal level via resistive divider for example?


    Also, do you need to have a capacitor between the D75F and the above mentioned xtal input pin?


    Has anone some pics of their LNB onboard D75F mod?


    73