Posts by oh2aue

    I tried 64.5 mm - the axial ratio is excellent, 1 dB, but the VSWR rises to 1.3:1.

    Hi there Mike,

    happy to see the two resonances in the SWR plot - and symmetrically about the CF of interest too, essential for good axial ratio in this type of design. And yes, at the minor cost of slightly increased SWR at the sum impedance spot frequency:…ment/2149-newpatch-7-jpg/

    Cheers - Michael, oh2aue


    did you describe somewhere which components with which values you added? Would be interesting for me to know!




    just made some practical listening tests with two modified GM201's and they work very well indeed. Used both my old jittery FRG9600 with built-in biasing and my older Funcube Dongle with Spectravue.

    I am referencing the LNB PLL with a Leo Bodnar GPSDO programmed for 25 MHz exactly. As noted, it was important to sufficiently increase the impedance of the regulator line so that it does absorb the reference signal as Ole noticed in his experiments. I replaced the ~270nH 0402 inductor with an 11 ohm 0603 resistor and added a second one (11ohm 0603) at the beginning of the meantered choke line - you need to cut the trace to use the two pads on the PCB (makes you wonder, doesn't it?). The LC series circuit is 12pF + 0,47 uH + 2,2 uH, all size 0603.

    The larger chips make it possible to build the circuit as a sturdy "bridge" as you can see in the photo. All five chips are visible in the same photo.

    /Michael, oh2aue


    on the Octagon Single this was not necessary - to understand why, I really need to take closer look at the IF DC Bias/Regulator circuit next time I have one open.

    But with the 3€ GM201 I had to apply about +16dBm to achieve PLL Lock and this is precisely due to the same reason, there is the L band printed choke, followed by a 0402 270nH chip inductor and then a huge capacitor to ground at the input of the 5V regulator/switch chip.

    /Michael, oh2aue

    That is what the Bias-T reference injector I designed for BATC is for…ence-injection-blank-pcb/


    Nice board!

    This is what is needed in the "Bias/Triplexer" box in the lower left corner of:

    The LO reference channel low pass function is necessary in case the synthesizer reference signal source isn't pure sine - any weak harmonics in the IF band could be quite annoying in waterfall analysis.

    I see the board might also be fitted with a low pass/band pass combination for the reference signal path in case you are using a 22 kHz DiSEqC signal. This signal is also why I use a simple series circuit in my modified LNB's; the band pass function reduces chances of the DeSEqC signal modulating 22 kHz sidebands onto the synthesizer LO.

    /Michael, oh2aue

    My solution for LNB modification. I tried several different capacitor values, but 15pF capacitor works the best for me.

    I also noticed that the LNB sensitivity drops down for about 3dB. It is stlll acceptable for NB, but not for WB on a 80cm dish. I don't know why yet. For WB receiving, I just remove the SMA cable from LNB and it works without external 25MHz reference.


    in my modified LNB's I inject the LO reference frequency into the IF cable via a very simple series resonance circtuit and extract it in the LNB directly from the F connector via a similar series LC circuit, routing it to the synthesizer with a short length of wrap wire and the original crystal removed:

    It is very important the series LC circuit is directly at the F(f) connector as in the photo to ensure stability of the LNB.

    Your LNB uses a very different design regarding frequency response, where selectivity is largely arranged by the RF bandpass filter. You can shift this down reasonably easily, but loading it dielectrically with a small piece of PTFE or Rexolite (Trolitul), about 2 - 3 mm thick. It is best if you can at least monitor the noise response with a spectrum analyser.

    In the models I use (the Octagon OSLO, Single output), is seems there is an image reject mixer in the IF processor (very difficult to find data on this, though something in one of the Chinese PLL LNB patents). Hence a bandpass filter is not required for image selectivity (and it can be argued how necessary it is in the first place, especially if the transponder noise is dominating your sensitivity anyway). Without the bandpass filter, the only frequency selectivity comes from the front end matching circuitry, waveguide cutoff, IF matching circuitry and from my own highpass filter in the triplexer at my receiver end of the IF coax.

    Here is quick measurement I made to figure out the IF response (in my version, the sensitivity is the same at IF's of 432/435, 739 and 950 MHz):

    As you can see, it is quite amazing that 144 MHz works for me: the gain is down considerably, BUT the noise figure is still about the same.

    /Michael, oh2aue


    the series resonance of a crystal is extremely narrow and will be very selective.

    Telefunken used to use this idea in an old 4 GHz microwave radio link crystal multiplier chain LO to reduce sidebands and very close-in phase noise. This solid state LO replaced the original reflex klystron LO, that was locked to mains 50 Hz by a mechanical cavity modulator modulated by AC - a bit of interesting trivia ;-) Maybe the patents can be found online, around 1950'ies ?

    My model of Octagon Oslo synthesizer uses 27 MHz originally, So far, for 10489.550 MHz receive, I have amongst others successfully used:

    Ref LO IF
    27.000000 MHz 9750.000 MHz 739,550 MHz FRG-9600, AR-5000)
    27.851400 MHz 10057,450 MHz 432.100 MHz (IC-402)
    28.648938 MHz 10345,450 MHz 144.100 MHz (IC-202S), unreliable PLL

    There are some '60 second videos' on my YouTube channel.

    The 144 MHz case is just on the limit of locking and is obviously pushing things too far. I have also experimented downwards, 26 MHz and even lower and the PLL/VCO locks fine (only one specimen tested at room temperature).

    There appear to be several other models and brands on the market that might be useable, but the true availability (older models) and image rejection/noise figure (cheaper models) needs further investigation. Most seem to use 25 MHz as the reference crystal and based on the NXP family of synthesizers.

    /Michael, oh2aue

    Hi all.

    I finally got round to testing the Octagon Oslo (originally 27 MHz reference) with a reference of 27.851400 MHz (Leo Bodnar Dual Output GPS Reference) to provide a direct IF output on 70cm. Highly empirical tests indicate that the front end/image reject mixer is working just as well as with the 739 MHz IF. Synthesizer locking and IF gain are still perfect. PLL & VCO locking is even OK all the way up to beyond 28 MHz and to make a pretty extreme test, I also tried a direct 2m IF, which worked, but already showing signs of instability issues (tuning range of VCO). Here is a short video of the Octagon LNB with 70 cm IF (receving with LNB only, no dish !!!):

    /Michael, oh2aue


    just for fun, here are a couple of videos of a standalone (no dish), modified Octagon Oslo PLL LNB. Referencing is from a Bodnar dual output secondary GPS reference with the first video of a KiwiSDR (binning equvalent to a wide CW filter) on the IF and the second with a Barlow Wadley XCR-30 (fairly wide ceramic SSB filter) on the IF.

    Basic hardware block diagram and other info:…nlink_pll_lnb_kiwisdr.htm

    /Michael, oh2aue


    thanks for the info, I only found photos of bares PCB's and drew the hasty and false conclusion the Mini-Tiouner it was only available as a kit (I hate having to create accounts just get basic information - grumpy old man syndrome).

    I was not aware of the SUP-2400 and it's us for DATV in DL/UK. But looking at the photos, I am pretty confident it is just fine for even pretty low symbol rates. And without any need for modification!

    /Michael, oh2aue

    The MiniTioune looks like a nice solution, but I prefer to spend my little spare time working on other things... :-)

    I recall the US HD satellite system DirecTV uses an IF of 250 - 750 MHz. To be able to use standard off-the-shelf DVB-S(2) receivers, there is a unit on the market called the BBC, B-Band Converter. This takes the DirecTV IF of 250 - 750 MHz and upconverts it to 1650 - 2150 MHz. Though I have never seen one of these in real life, let alone had one in the lab, I think chances are the LO (low side 1400 MHz?) is stable and clean enough to also allow demodulation or our lower symbol rates. The unit is power from the satellite set top box LNB connector.

    There are BBC units on Ebay and Amazon for about 10 - 20 €, but the US shipping is a whopping 25 - 40 € and on top of that there is the customs etc.

    I wonder if anyone has happened to already taken a technical look into this possiblity?

    /Michael, oh2aue

    Ah, yes, non-trivial RF test engineering, one of my favourites :-)

    Regarding NPR (Noise Power Ratio) linearity measurement:

    This was the toughest possible test back in the days of carrier transmission in telephone networks (ITU-T G.228, "Measurement of Circuit Noise in Cable Systems using a Uniform-Spectrum Random Noise Loading".

    For HF radio, I usually use a modified Wandel Goltermann RS-5 or a modified Hewlett Packard 3708A with WG crystal or homebrew, purpose build notch filters.

    HF setup for testing SDR-IQ:

    Example of a the notched spectrum (linear) above (10 kHz/div, 10dB/div):

    Full HF span:

    Insufficient measurement points in the SPA plot to correctly indicate depth of the narrow notch - once again, an analogue spectrum analyzer with a realy CRT would be the winner...

    Obviously it is possible to upconvert this signal to VHF/UHF, even SHF, provided your upconverter is vastly more linear than the DUT ;-)

    For SHF I usually build a wideband noise generator/amplifier/filter combo to achieve the necessary spectrum for loading/linearity testing. The rest of the measurement is straight forward RF stuff with couplers, power splitters, power meters and spectrum analyzer.

    As an example, here is a linearity NPR test setup for a QRO 13cm SSPA:

    NPR is just the ultimate linearity measurement method ;-)

    But for most purposes and intent, the traditional two-tone test or just plain -1 dB compression measurement is sufficient for setting bias etc. Some are happy with just guessing the bias and drive, but personally, I prefer facts ;-)

    /Michael, OH2AUE

    Hi All,

    thought I would share my plans for station monitoring in case somebody finds this useful. My approach is maybe a bit heavy duty for some, but this is how I am ;-)

    I have been scrounging bits and pieces from my junk box to put together a "Loop Test Translator". This is essentially a box that takes a sample of the 2.4 GHz uplink and downconverts it directly back to the downlink band on 10 GHz. For Es'hail-2 this means a local oscillator of 8089.5 MHz. This was something I already did many years ago when we (AMSAT-OH) were still developing the P3E/P5A linear/ranging transponder - it made testing the linear transponder a breeze.

    So far I have put together a 40dB RF sample port on a 2.4 GHz load that will absorb my uplink power (you could simply use a directional coupler in the antenna line and point the antenna to zenith for safe testing). This sample is further attenuated and fed to a surplus microwave mixer (Anaren 74129) and the LO is a modified PLL multiplier "brick" that I have retuned for 8.1 GHz output and uses a reference crystal of about 96 MHz that I found in my junk box (this experimental crystal is still about 3 MHz off at X band). Ideally, this should be 96.30357 MHz (84x) or preferrably 101.11875 MHz (80x, in my particular case) to achieve 8089.5 MHz exactly. The upconverted 10 GHz signal is then filtered, attenuated further and coupled to the input of my modified PLL LNB (SPC Electronics) using a waveguide directional coupler, just after the antenna feedhorn.

    In this way, it is possible to make a very quick test for overall station end-to-end performance, also on the WB transponder.

    Michael, OH2AUE

    James, G3RUH developed and add-on ADC for his demodulator enabling FEC decoding already in 2003.

    Back then I also used the AE4JY demodulator for FEC, but you will recognize I am an old-fashioned Physical Layer guy, because I prefer hardware demodulators (logic chips and OP amps!) with real-time displays (analogue oscilloscopes!) of Eye-Height and Constellation ;-)


    Michael, oh2aue

    OK, so I have been annually dusting my G3RUH 400 bit/s modem and testing my AE4EY AO40rcv SW with my library of AO-40 audio files. My favourite one is:

    Is anyone aware of any efforts in writing a suitable decoder for P4A telemetry to match the older AO-40 demodulators?