Receiving system not based on Octagon LNB

  • Hi George


    If you look at the xtal terminals with an oscilloscope - before removing the xtal of course - it is easy to see which is input and output of the onchip oscillator. The terminal having lower amplitude and cleaner signal is the input. Where you can inject external LO.


    73 Ole

  • Hello, At last found an LNB in Turkish local market

    RX sensivity is not good as octagon according to my humble comparison but it has NXP PLL circuit.. and crystal . Stable enough for SSB rx.


    It is same board as Opticum Robust

    It is sold as MAG PLL LNB Single in Turkey.

    I also had a twin model..which has DRO in it.

    Thanks to TA1D for opening up the single model and finding this.

  • Hello guys, I’ve started experimenting with a cheap starcom, which have a 3566 pll and a 25MHz xtal , does anyone know if this chip can handle a 24Mhz clock (which would make a Neo7 module a good candidate for gps clock reference)? I could not find a data sheet...


    73 iz2eeq

  • Hi IZ2EEQ
    I don't have an answer to your question but rather a few comments.
    Comment 1 - Neo7 GPS and jitter.
    I think the Neo7 is not suitable directly as a source for injection locking a LNB. I have a lot of experience with the Neo6 line and also tested a Lea8-T and they are very jittery on the output.
    The Lea8-T is specifically made for timing applications and therefore have a more advanced TXCO compared to the simple oscillator in the regular Neo6 GPS modules. But they are both way to jittery for use as a reference.
    I have not tested the Neo7 line but I would imagine they are not much different.
    Even if you use an output frequency that is an integer from the internal 48MHz oscillator the frequency corrections are very jumpy and random in both short and long time scales. 24MHz is a good output frequency for these as you avoid fractional division spurs but even at 24MHz they are super jittery.


    Comment 2 - Why not use a 25MHz TCXO for your Starcom LNB ?
    I would recommend the Abracon ASTX-H11 series of TCXO, they are available in 25MHz frequency and not to expensive. They have built-in electronics that counter-adjust the frequency drift of the built in quarts and are really nice TCXOs.
    They have an absolute precision of 2.5ppm but drift due to temperature changes is lower, around 0.5ppm.
    If you have it in the shack and feed the 25MHz on the coax the resulting frequency drift should be quite low and "good-enough".

    73

    //Harry

  • Hello Harry, thanks for your comments. I had read the NEO7 was much less jittery when divided by powers of two but, as it turns out from your experience, it is not jittery free enough to be used on its own. Yet I wanted to go for a GPS disciplined solution, so I will end up using NEO as a reference together with a controlled oscillator and see where it gets!


    73 iz2eeq

  • Good morning,


    I do not understand the wobbling issue. Some LNBs do, some not, even using the same PLL chip/design. Then I read that the x-tal may cause this. Because these LNBs are very cheap the parts must be extreme cheap too...


    When I stay at the original frequency (27 MHz for my HD LIne Black Premium) and replace the x-tal with the connor winfield analog TCXO that Heiner DD0KP (I think was it) recommended, then the frequency should be stable without wobbling...


    What do you think?


    73 Mike

  • On my Triax LNB as documented here, the wobble completely disappeared when I fitted a Si Time 0.1ppm TCXO.

    Dave Cawley | Ex G8EAO & G6ANG/T |
    (when you had to have a separate TV license !)

  • I've tested the HD Line BP2 for some hours now after getting SDR Console running on my computer. I cannot say it wobbles. It does drift of course but beacon tracking enabled it's not really bad in unmodified condition.

    To bring the Connor Winfield TCXO into this LNB is a problem of space. It's probably better to make a DC and TCXO injection from the shack.


    I observed some rough SSB signals (with a slight aurora tone like on 28MHz/50MHz) when using a Voltcraft 12V switching supply for this LNB. But today I used an Mean Well switched power supply and it was OK. We will see...


    By the way: has anybody adopted this not quite round waveguide to the POTY feed (

    designed by Mike Willis G0MJW, Remco den Besten PA3FYM and Paul Marsh M0EYT)?

  • DL1GNM the simplest way to put a lnb to the poty antenna is using the venton exl-s this is the only venton with pll inside..you can fit it after not more then 5 minutes to the waveguide.. i will post how to do this later over the weekend.

    attached a photo how it looks like...


  • Very suprising I first did a test on the WB bakon with the lens from PE1CKK. the mer was 4,2. then I remembered the the venton lnb was able in this dish to get a mer of 7..

    Then I took the original venton lens and put it on the end of POTY. What I can tell you..I am very glad to have now a mer of 7 again.. big surprise..

  • That is how my new setup looks at the end.. receiving works fine now.. but for tranmitting I first have to get a weatherprove box for putting upconverter and PA near to the new antenna.. In the background you see my 60cm dish which I use for tranmitting at the moment..and beside the powersupplies.. and upconverter PA and filter.. this will be moved to the new dish.. and when my andrew PA is ready you can also see me on DATV..

  • Let me add my experiences modifying a Starcom SR-3602.


    I'm a satisfied user of the PE1CMO transverterkit, which comes with a SR-320 that has been modified. Modifications include changing the powersupply from the onboard stabilizer to the low-noise power supply of the CMO kit, and to use the 25MHz reference from the same CMO kit instead of the internal crystal.


    But, the SR-3602 is a twin LNB, and I could use the other LNB port for the WB transponder, or as an aide to point the dish (over here, the British 28.2 position is usable and close).

    I didn't want to adapt the supplied SR-320, prefer to keep it as received from Rene (so I have a "good" reference), also I wanted to get some experience making these modifications.


    Via aliexpress I bought 4 SR-3602's cheaply, if we were to ruin one during my experiment it would be no big loss. At time of writing, I indeed succeeded in ruining one in the process.




    To begin, the electronics is very different from the SR-3602 Remco PA3FYM described earlier. Note that the PCB is only half-size of the diecast box and the very RF-way to bridge the space between the edge of the PCB and the F-connectors (several cm!).


    Incidentally, the plastic enclosure of the LNB has a sticker with type and serial number. On my LNB's, all four have the same serial number.


    In contrast to other reports, the lid is not screwed-on but held with glue. Cut through the glue, use the tip of the knife to lift the bottom left corner and you can lift the lid.


    On the PCB there is a 25 MHz xtal (thankfully the same frequency as the shippedSR320), and one receiver chip (RDS 3567E) that feeds both IF ports. PE1CMO described the circuit earlier and it is the same here: on-PCB choke to isolate the IF signal, 78L06 stabilizer and various capacitors. The output of both 78L06's are combined with diodes to supply the receiver chip.


    During tests with the LNB un-modified I had found that the right IF port (near the horn) already gives a good signal, but the left port (away from the horn) has some aurora-like instability, unimportant for television but it may affect our SSB signals. So, I will modify the right port for the NB transponder.


    To modify the power supply, remove the 78L06 (not easy if you don't want to damage the PCB) and replace this with a parallel resonant circuit of 150nH and 270pF with coil stacked on capacitor, using the pads of the 78L06. I had 0805 SMD's; if I would do this again I would use 1206 SMD's for this.

    The input of the 78L06 (on picture, mid and top connection of the right stabilizer) has a capacitor of 200nF or so, which I removed as not to attenuate the 25MHz reference signal.

    To the right of the stabilizer there is another capacitor, which I removed as well.


    The best way to do this is to do one modification at a time, then test if the LNB still works. More on that below.


    Second modification step is to replace the 25 MHz xtal with the reference carrier from the IF port (supplied by the CMO xverter). The picture shows the two crystal connections, the LEFT one is the input. In the top left of the PCB there is a trace that goes to the RIGHT pad of the crystal (formerly, output). I cut that trace, this is easier than trying to lift the crystal (it is hard to get enough heat on the xtal to avoid lifting solderpads). Moreover, as suggested by PA3FYM I wanted to use the crystal as filter towards the IF port. Unfortunately, I could not get this to work, but a series resonant circuit (again, 150nH and 270pF) between IF port and left xtal pad, made things work.


    So far so good, but in my case something unexpected happened. After modifying the power supply, the receiver chip would not work. Normally, connecting the LNB results in a significant noise increase, but no more after I had mod-ed the power supply circuit. It took me a while to figure this out.


    The IF-port circuit has multiple, different functions: power supply (which I had modified), IF output (not touching that), but in addition there is circuitry that makes the LNB switch H/V polarisation on 13V vs 18V, and change LO frequency if a pilot tone (22 kHz) is sensed.

    On the photo, right-below next to the receiver chip there are 3 resistors and a capacitor. That is the switching mechanism: 560k to input voltage, 63k to ground, and a series resistor of 1K towards the input of the IC.

    This circuit is a 1:10 attenuator: 13V input gives 1.3V on the receiver chip, 18V gives 1.8V. The 560k resistor is bypassed with a capacitor, probably to avoid attenuating the 22kHz pilot tone.

    When the power supply is changed to 5V, the circuit only gives 0.5V and it seems this causes the RDA 3567E to switch off. Fix is simple: replace the 560k resistor with an 180k resistor. I removed the capacitor at the same time, didn't want the 25MHz reference signal to confuse the receiver chip and everything started working again.

    I suspect this logic was added so that if an IF port is unpowered, no IF output should be on that port. Keep in mind that if one of the IF ports receives power, the receiver chip is powered because of the diodes after the 78L06.

    I didn't read anywhere about this arrangement on a forum so I hope this report helps.



    Other thing: I was worried that the lens of my POTY antenna would be damaged if the antenna would be dropped. I have now put the POTY in an enclosure RND 455-00198 (available at Reichelt in Germany), where I also ordered the SMD's. The enclosure doesn't seem to attenuate the signal and doesn't heat up in the microwave oven.


    Hope this helps,


    Geert Jan