Modification of Octagon Oslo PLL LNB for External Frequency Reference

  • Yes.. and in HB9, the responsible federal department has banned the UV-5R altogether (no sales, no ads, no usage, not even giving away for free). Not to say that all UV-5Rs are bad, but apparently too many..

  • I have a mix of results with Chinese electronic devices. Never bought a Baofeng HT and never will but, I admire those scientists behind its creation. By using the 437.065MHz 24th harmonic, I was giving the chance to witness how much my Octagon Optima OTLSO improved after incorporating the upgrade suggested by G0MRF. The 27MHz Connor Winfield TCXO makes it pretty drift free if compared to what it once was.

    I also use the 739MHz to 144MHz downconverter by G0MRF. You may say I can get by with a NooElec us$35 SDR and a computer instead of my all mode 2m rig. I do agree but I don't have plans to either sell the radio or give up on its bells and whistles including the VFO knob feeling. Let's say I like sailboats and horse riding.😃

    Having said that, watch the two videos I recently uploaded and make your conclusions. Comments are welcome. I do appreciate your return.


    Luciano PT9KK

  • There is a PCB for my design available from Luciano PT9KK, an AMSAT member in Brazil. (See post above....Hi Luciano ! )

    It Uses a Si590 oscillator module on 595MHz from Digikey.

    Includes a bias Tee for feeding the LNB and 2 outputs, one attenuated at 739 and one at 144MHz for the narrow band transponder.

    David G0MRF

  • Hi, Adding a TCXO in the LNB and then a down converter to bring the final signal to 144MHz is a solution I’m very interested in trying. I haven’t opened my Octagon LNB yet so I’m not sure if it is of the 27 or 25MHz xtal variety but see that both frequencies are off the shelf D75F from Digi-Key.

    Having only recently rejoined AMSAT-UK I don’t have access to David’s design for the down converter. I would certainly be interested in purchasing a PCB from Luciano if there are any spare and would also appreciate a copy of the original article/schematic.

    Clive G4KCM

  • The frequency stability with the D75F is far better than with the original xtal but in comparison to my solution with software correction it it really bad.

    I have now managed with my solution to hold the frequency stable with drift less than 20Hz over 25 hours. (The LNB drifted about +/- 10kHz over this time)



  • Is that an SDR-based software approach? There is that idea of locking the SDR to a carrier within the received band that is known to be stable. The beacons could be used for that purpose (after removing the BPSK modulation of course).

    The user would then see a stable tuning dial / waterfall while the software actually adjusts its parameters to keep the beacons at a fixed frequency.

    (it would be best to do this in de demodulator and not by varying the LO frequency of the receiver, as that usually leads to momentary loss of lock)

  • 'Stability' is a bit of a moving target and means different things to different people. The software solution or an external GPS locked source fed down the cable to the LNB are at the top of the list on performance. However, it's worth remembering that we are nearly all used to tracking doppler, so a bit of drift is not going to be a disaster. The reality is surely that over the time of a QSO we do not have to retune. For SSB that could mean 100Hz in 20mins is acceptable. But for JT-9 you would need better than 3Hz in 1 minute. So perhaps look at what you need in terms of performance and then decide how to get there. - See you on P4A !!

  • Could you please specify which test you are referring to? Actually DG0OPK confirms the excellent behaviour of the D75F.

  • Looks like i have interpreted the frequency on the x-axys wrong (2/20khz), my fault.

    We will see what operating setup will work best when we are allowed to transmit to the sat.



  • My experience with a freerunning StarCom SR-3602 PLL LNB so far is that it is acceptable for "amateur SSB use" under quiet weather (and hand-on-dial) but when it is rainy/windy or when it is sunny and the sun has just raised or set, not so good.

    Of course it is good for first tries. And I just received my 4-output LNB that I will convert to external reference.

  • This weekend my StarCom SR-3604 arrived, the 4-output version that I ordered intending to convert it to use an external reference.

    Because the housing has 4 F connectors, it will be easy to use one for the reference input, and have 3 outputs for the Phase4A receiver and my normal satellite settopbox (2 tuners).

    Now I opened it, I have seen something interesting: there are actually 2 separate 2-output legs in this device, each with a PLL/mixer chip of type "1051" (I have not found anything about it yet) sharing a single unmarked crystal (probably 25MHz like the marked one in the SR-3602).

    I'm going to try to convert one leg to use the external reference and a single output, and keep the other leg on the crystal. So I can watch TV without the reference connected.

    (there are 4-output PLL/mixer chips as well but apparently they did not decide to use one of those)

  • SORRY: This part is digital not analog and therefore could not be used..

    For those of you who have old Octagon LNBs with 27 MHz crystal here is a cheap solution with 26 MHz TCXO from Ebay 1,50 Euro pcs plus 1,60 EURO S&H

    Datasheet is attached.…ksid=p2057872.m2749.l2649


  • Good morning,

    I am using here an Octagon Oslo Optima LNB and a sdr usb stick. As reference frequency source for both devices i made a small circuit from parts lying around which delivers 25MHz for the lnb and 28.8MHz for the sdr stick disciplined via gps. The arduino sketch is programmed in a very direct stile.....not very nice, but working. The sketch needs two libraries: and



  • Good morning Andreas,

    my plan is a simmilar solution. i will use the 3 outputs to build a stable ssb station with FT-290 for TX INTO BU-500 and FT-790 for RX. All should be locked to GPS timebase. This should work as a portable station without the need of a PC. regards Heiner..

  • hi david,

    where can i order this board ?

    please info.

    tnx de wolfgang - do2sw