Pollin LNB GM201

    I am currently using the StarCom SR-3602 with the RDA3567 chip and it is OK, it wobbles but only dependent on the temperature. In quiet weather I can keep tuned to an SSB QSO quite well, but when it is windy and raining it wobbles.

    And of course it is not stable enough for digital modes.


    However, as with the other types mentioned here, I have heard that not all SR-3602s are created equal. Your mileage may vary.

    I also have a SR-3604 (4 output version) and it has 2 completely different chips, KTB1051, not a 4-output chip and not the RDA. I have not tested it with the satellite yet, only opened it to see how easy it would be to modify for external reference.

    (I have not been able to get datasheet or application note for the KTB1051)


    Currently I am experimenting with the beacontrack code from PE4WJ and this improves the stability a lot. Long-time drift of course is zero, but it also tracks the wobbling quite well.

    Hello all, thanks for the answers to my question regarding the 70cm IF. Meanwhile i got a Signal on 70cm with that Pollin LNB but not on the expected frequency. The Quarz from eBay from austria was indicated with 25,788MHz. I expected the beacon on 432MHz but i found the beacon on 430,081MHz. Its difficult to have two parameters wrong (frequency and direction). Maybe the Quarz was wrong or the PLL factor i assumed was wrong?


    Btw. I was wondering about the good stability of the Pollin LNB. For SSB it was fine for me. With additional aluminium foil arround its ok.




    73 de Kai

    The PLL factor is 390. This means you have to be only 5kHz off at the crystal frequency to get an error like that. This is not unusual when the crystal cut does not match the circuit you are using it in. E.g. when you order a crystal for series resonance and in reality the circuit is for parallel resonance, or the loading capacitance is different.

    Fortunately it is always easier to pull crystals down than to pull them up.

    So you could attempt to correct (part of) the error by using a small parallel capacitance or a small series inductor.

    However, such pulling will reduce the stability of the oscillator, so it may be worse than what you have now.

    Depending on your local bandplan this may be a quiet portion of the band.

    (not here, it is the band segment where the FM repeater outputs are)


    It looks like you have quiet weather there. Then, my freerunning LNB is quite stable as well. But the past days it has been rainy and windy, and then it is much less stable. The beacon locking helps a lot. You could try that too.

    (or wait for a more ready-to-use solution)

    Like my (late) neighbour Arie PA0EZ used to say: "Know your frequency and I'll find you". You don't know your frequency (especially with a multiplying factor of 390 (or 361.1111...) using a crystal or TCXO at 10(.5) GHz with these PLL LNB's.


    Definition of 'know your frequency' = accuracy of (I try to be polite, honestly I am a nice guy and no pun intended...) 10 Hz = 1 ppb @10(.5) GHz.


    So ..., lock to GPS (or another standard which has 1E-10 (or less) accuracy)!

    My LNB is about 220 kHz out (oscillator too high), I would not consider that excessive, the spec is usually +/- 1 MHz.

    Remember the crystal itself is off by only about 500 Hz in this case, 22ppm.

    The commonly observed variation is like 40 kHz peak/peak or about 4ppm.

    All typical values for a crystal oscillator.

    Hallo....


    Yesterday I did experiments with a LNB GM201. Via a C 220pf I feed the signal from the GPSDO via a cable RG 178 at the upper end of the quartz (center) and GND. In the cable I have an attenuator of 6dB installed.

    The PLL rested with me !! from about 26.569 to 23.577MHz. Since this morning the LNB works with 26.525641MHz (10345MHz) and I can receive on 2m. Now tests have to show how stable the whole works over a longer period of time.


    73

    I bought 4 of those cheap LNBs and modified one with a 24MHz crystal for LO shift to be able to receive the promo video on WB transponder with a normal receiver.


    So far i can say that it wobbles much more than the Octagon OTSLO.


    Could be caused by the cheap crystal or maybe the LNB is more sensitive for movements due to the strong winds here today. (the OTSLO wasn't wobbling!)


    Also i have not tested it yet with the original xtal and so i can't say if it stays more stable with the original xtal.


    Maybe tomorrow i will install a unmodified one and carry out some tests with that.


    vy73 DB8TF

    OK, the promo video on 10882MHz (LO 9360MHz with 24MHz xtal) is stable with quality 67% on my 130cms RX dish.


    For that purpose the GM201 with changed xtal works ok.


    Now it's time to take a closer look at the "wobbling" on the NB transponder.


    vy73 DB8TF

    Do you know what mixer/pll chip the GM201 uses?


    73, Edson PY2SDR