Posts by oh2aue

    S/N ratio is, especially for CW, a function of detection bandwidth, or in the case of an SDR, a function of sampling rate and fft size. For a regular analogue radio with real HW filters, the CW power is (hopefully!) considerably more than the noise, so the (peak) power measurement will fairly accurately depict the carrier energy level with even quite wide detection bandwidth. For noise however, we need to consider the noise bandwidth. The broadband, filter passband-filling noise power (which should be detected in RMS by the way) will be highly dependent on the bandwidth of it, i.e. how much noise energy is being integrated into a number. Increasing the detection bandwidth from e.g. a ~300Hz CW filter to a ~3kHz SSB filter will result in 10dB more (noise) power. In other words the CW carrier S/N ratio will appear 10dB worse with a 3kHz filter than a 300Hz filter


    The point is, to make any kind of S/N ratio comparison, we need to know the modulation (CW is very different from 400BPS PSK) and we need to know the detection bandwidth. And in the case of SDR it is important to know the sample rate and FFT size (bin count). Only in this way can we compare apples with apples or make orange/apple conversion calculations to make comparison possible.


    And for really meaningful S/N measurements, peak detection should be used for the (CW) carrier (S) and RMS detection for the noise (N).


    It does not hurt to realize that the noise factor (N) is often noise + interference (I) and that a more accurate measurement would be S/(N+I), but fortunately for us, due to it's very high linearity, the QO-100 transponder noise floor has been and is pretty much random noise. In AO-7, AO-40 and the like, this was not so simple as HELAPS and other high efficiency RF amplification and other linearization and non-linearity processes resulted in noise-sounding (N+I.)


    The result of all this is that 9dB SNR can easily be the same this as a 25 dB SNR. Only the measurement conditions are different.


    73 - Michael, oh2aue

    Not sure what you are referring to?

    My frequency is is extremely stable.

    What you hear in the audio pitch is Doppler due to my accelerating and decellerating?


    The name of the video is "Compensating for QO-100 Doppler with Fuel Injection Rate" :-)


    Accelerating from zero to about 80 km/h will shift the received frequency up by almost 800 Hz

    as I am clearly approaching the satellite. This is why copying SSB mobile is a bit touchy.

    I really want to correct the fake news on Doppler Correction with Geostationary Satellites.

    Sometimes Doppler Correction is mandatory for pleasant copy:


    https://twitter.com/oh2aue/status/1176124628043014144


    (Copying the QO-100 CW beacon mobile, so far about 50km worth of experience)


    In my junk box I have a Qualcom Euteltracs/Omnitracs microwave head with stepper motor driven pillbox antenna, vertical polarization and all. This might even make SSB communication possible...

    Modified "My First Venton" for single coax operation.


    Needs about 0 - +3 dBm. I have 12pF + 2u7H in series from the F-connector directly to a crystal pad (crystal and caps remove). Cut a small slot in the cover wall to accomodate.


    Also removed the second crystal line to improve stability. On the DC line I have 10 + 12 ohms in series. Operation is very reliable with +9Vdc.


    I also modified a DX Patrol LNB PLL Reference & Bias-T unit for single coax use as per my triplexer design, but this still needs a more accurate 10 MHz external reference as the DX-P TCXO is 65kHz too low @ 10 GHz.


    https://twitter.com/oh2aue/status/1172176646478213121


    Michael, oh2aue

    Actually, I recall we (AMSAT-DL, specifically DJ4ZC) were looking at an LD cut crystal affair from the woods of Neuchatel for P5A. It takes some stability to demodulate 3bit/s BPSK from a Mars-orbiting spacecraft transmitting on 10GHz into an omnidirectional antennna in "emergency mode"... Those were the days...

    Don't trust devices that have no specifications. Particularly programmable TCXO's.


    As a reference to what can happen with an advertised "TCXO" that is actually some sort of NCO, I made some measurements with two models available on ebay.


    My friend first tried a couple of 25 MHz versions with a "201" LNB and all was fine and dandy with both the NB transponder and a homebrew signal source. These "Ultra Precision Golden Oscillator Clock" devices were advertised as programmable to the customer specification and were programmed for the 25 MHz needed here (for the 9750 MHz LO).


    As most LNB's perform extremely well also with a direct 70cm IF, it was decided to experiment with TCXO's programmed for this IF too, i.e. LO = 10057 MHz, so 25.787179 MHz. This is where the fun started: the signal from the TCXO looks fine on an oscilloscope and the frequency can be verified with a frequency counter, but absolutely nothing can be detected at 10 GHz, nor with the transponder nor with the homebrew signal source.


    So the TCXO's had to go into the lab. The SSB phase noise at 25.000000 MHz is pretty high, but only just low enough to end up with an SNR of about 20 dB (in a 3 kHz bandwidth) with a strong CW signal at 10 GHz (cavity VCO driven Step Recovery Diode 10369 MHz PLL Brick Oscillator with +13 dBm output). But the 25.787179 MHz SSB Phase Noise is about 20 dB higher and after "multiplication" by 390, the 10 GHz LO is nothing but a pure noise hump, i.e. even a very strong signal cannot be detected in SSB mode!


    Self-deception is very easy when using the 25.000000 MHz version as the signal to noise ratio is fairly good. But it takes some effort to realize that the SNR-limiting factor at 10 GHz can be the PLL LNB/TCXO combination and not the transponder per se.


    Actually, if the SNR on the transponder downlink were 20 dB for a given signal, along with the ~20 dB SNR offered and limited by the TCXO * 390 Local oscillator, the total SNR would be only 17 dB. Tolerable, but quite a bit more would be available with a good old ovenized crystal oscillator reference or even the Bodnar GPS Mini.


    Even my quite average R&S SMX signal generator offers better performance than the 25.000000 MHz version of this "TCXO". Yes, the TCXO frequency accuracy and and long term stability are pretty good, but the phase noise is horrendous at the highly multiplied microwave frequencies we desire. It is not even particularly good at the primary frequency. But yes, it was cheap.


    And the 25.787179 MHz version is just a ~1 MHz wide noise hump at 10 GHz.


    Some plots:


    https://twitter.com/oh2aue/status/1161377560279900165


    When it comes to affordably priced SSB Phase Noise performance, there still is no competition for a well designed, ovenized crystal oscillator, in use since the early twentieth century ;-)


    Michael, 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:


    https://forum.amsat-dl.org/cms…ment/2149-newpatch-7-jpg/


    Cheers - Michael, oh2aue

    Michael,

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


    thanks,

    Robert


    Robert,


    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


    Ole,


    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.


    https://twitter.com/oh2aue/status/1103741519561965568


    /Michael, oh2aue

    That is what the Bias-T reference injector I designed for BATC is for


    https://batc.org.uk/shop/lnb-b…ence-injection-blank-pcb/


    Hi,


    Nice board!


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


    http://www.fletcher.fi/eshail2_kiwisdr.gif


    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.


    Hi,


    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


    Jerry,


    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

    Hi,


    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:


    http://fletcher.fi/amsat_oh_ra…nlink_pll_lnb_kiwisdr.htm


    /Michael, oh2aue

    Heiner,


    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