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
Heiner et al.,
just received some Venton EXL-S Rocket Single LNB's from Holland and I can cofirm they are PLL models:
https://schotelzaak.nl/winkel/…-exl-s-rocket-single-lnb/
The price is right, but the shipping is pretty expensive if you only buy one...
The serial numbers for mine are around EXLS-122016-005xx (December 2016?)
Michael, oh2aue
Thought I would set up a thread for unusual station setups 
Here is mine from today, receiving QO-100 rowboat style:
https://twitter.com/oh2aue/status/1165243013624422400
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
Hello Kai,
slide 16...
/Michael, oh2aue
Hi,
some experimental notes on modification. I have successfully modified two GM-201's so far, both used the NXP1017 IF processor and LS7005 intelligent regulator:
http://fletcher.fi/Universal_S…al_referencing_oh2aue.pdf
/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
Display MoreHello,
I'm also using single output LNB's - Octagon and other types - modified for LO injection through the downlead coax cable. I was puzzeled by the amount of LO power needed for the PLL to lock. In my case something like +3 dBm to + 7 dBm. It turns out that with single output LNBs, where the 25 MHz shares F-connector with DC supply voltage, the LO signal is loaded down by a capacitor - 0.1 to 0.33 uF - placed at the input terminal of the 78L06 regulator. Only a meander line RF-choke prevents a total short. This circuit is used on all LNB I have seen.
My solution was to put a 10 ohm SMD resistor in series with the meander line. It reduces the loading effect of the 0.1uF? capacitor and increases LO injection sensitivity by 15 dB. So now only -10 dBm is necessary. It also gives a 1 V voltage drop, but with 12 V supply to a 78L06 this is not a problem.
The LNB is not an Octagon, but a cheap 7 Euro PLL type bought locally.
Diplex filter in the shack to separate IF, 25 MHz and 12 V DC is homemade. Just a few components in a metal box.
73 Ole
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
Hi,
Nice board!
This is what is needed in the "Bias/Triplexer" box in the lower left corner of:
https://73.fi/oh2aue/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
Thanks Michael, i think if you inject 27.84184701 you are on 435,
27.8501547 should be 432 if i'm correct. It's nice to see the kHz on the 70cm are identical to that of the dwnlink, hihi.
Hi Jerry,
yes, I have been experimenting with quite a few different LO frequencies, depending on the capabilities and crystals in my Old Skool radios
/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:
https://73.fi/oh2aue/amsat_oh_…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
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:
http://www.fletcher.fi/hf_npr_testing_2018.jpg
Example of a the notched spectrum (linear) above (10 kHz/div, 10dB/div):
http://www.fletcher.fi/11700_kHz_brf_s21.gif
Full HF span:
http://www.fletcher.fi/11700_kHz_brf_s21_full_response.gif
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:
http://www.fletcher.fi/s_band_npr_test_set_demo.jpg
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
