Posts by oh2aue

    Hi,


    the triangular strip is propably fairly repeatable to produce without test gear, which is an obvious bonus.


    Here is an old design I made for our Ilmari balloon project (weight around 40 grams) that uses an oblong shaped matching section (don't seem to have a plot of thre return loss, but it is around 20 dB for the 23cm ATV band):


    https://73.fi/oh2aue/23cm_helix_1.jpg


    Though I still prefer the bother of making the capacitive base wire loading for good broadband matching (the markers are at seemingly weird frequencies as I wanted to get an idea of the attenuation at these) :


    https://73.fi/oh2aue/13cmhlx1.jpg


    https://73.fi/oh2aue/helix.gif


    /michael, oh2aue

    Your connection is not secure

    The owner of 73.fi has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website.


    Thomas,


    the site is about as secure as possible (I am sure you did use https).


    Please run:https://www.ssllabs.com/ssltest/analyze.html?d=73.fi&latest


    Results:

    73.fi Overall Rating: A+

    Your web browser must support SNI and use TLA 1.2 or TLS 1.3

    Firefox version 31 will not work, but then the current version is 75...


    Take care,

    /michael, oh2aue

    Just in case somebody does not have immediate access to old articles and magazines, here is my writeup on AO-7 from, like, >20 years ago. I realize some of the links are now obsolete and need to overhaul this page sometime soonish. For me, the most important are the block diagrams of the transponder, especially the HELAPS transponder.


    Things to do list: write an English Block Diagram...


    I also really need to take some time to write something on the 2.3 GHz S band beacon that never got tested in orbit. But regardless, many thanks to the San Bernardino Microwave Society for supplying the flight hardware, eons ago.


    https://73.fi/oh2aue/ao_07_history.htm

    or

    https://www.qsl.net/oh2aue/ao_07_history.htm


    /michael, oh2aue

    A dual band circularly polarized patch feed from the dungeons of Brno:


    http://www.urel.feec.vutbr.cz/…ts/Marsalek/DSCN0051r.JPG


    The very interesting thesis of OM Mirek, OK2AQ's student Aleš Maršálek may be found at:


    Multi-frequency reflector feed with circular polarization for a small parabolic antenna (2002)


    (1270 & 2400 MHz RHCP 50Ω design for f/D of 0.4 to 0.5)


    In particular, the evolution from a dual fed circularly polarized patch to a self-phasing CP patch is described in Chapter 4 with scetches of the underlying principles of dual resonances and related phasing in Figures 4.4a & b and 4.5. Otherwise there is a real lot of interesting detail in the work, but I do need to brush up my Czech somewhat ;-)


    As ever, the true bible of radio engineering by Frederick Emmons Terman contains all the answers to all possible RF questions or at least the beginnings of them. Personally I prefer reading one of my original hard copies, but the 1937 edition is also downloadable at:


    https://archive.org/details/RadioEngineering


    Figure 29 on page 56 tells it all.


    /Michael, oh2aue

    And Happy New Year :)


    A couple of examples of commercial patches for the GPS L1 frequency:


    https://73.fi/oh2aue/gnss_rhcp_patch_no1.jpg

    https://73.fi/oh2aue/odd_even_…ple_patch_no_1_oh2aue.gif


    https://73.fi/oh2aue/gnss_rhcp_patch_no4.jpg

    https://73.fi/oh2aue/odd_even_…ple_patch_no_4_oh2aue.gif


    Many of these commercial patches sub-perform, mostly because the design engineer will not read or implement the manufacturers instructions, especially regarding ground plane and weather protection dielectrics.


    But sometimes these patches simply have not even been designed for RHCP: there are also models on the market, where dual frequency operation is claimed, one patch direction is tuned for one spot frequency and the orthogonal direction for the other.


    Obviosly both are linearly polarized with the -3dB loss penalty.


    But happily we mere radio amateurs are smarter :-)


    /Michael

    PA3FYM,


    well, here in Finland we have this thing called "nollatutkimus", or zero-research, quite literally referring to putting effort into restudying something that has been evident for eons ;-)


    Something like this, only this is on 7 MHz:


    We all know that the polarisation ellipse of a correctly aligned POTY would on the polarimeter CRT be a perfect circle (when measured in a reflection free environment - here at the 62nd parallel north, snow melts and the garden dries to boot-comfort usually around April/May...).


    Meanwhile, I am integrating a Trio CO-1303D oscilloscope into the system, more pleasing for the esthetic eye with it's vintage round CRT and all that :)


    /Michael

    Trying to adhere to the topic:


    From the TX viewpoint, for simple circularly polarized feeds one still needs to achieve splitting of the signal into two equal amplitude components with +-45 degrees shifts, i.e. two orthogonal fields from two virtual elements with impedances of 50+j50 ohms and 50-j50 ohms. Parallelly fed this results in a total feed impedance of 50+j0 ohms purely resistive.


    These two resonances should be evident from the hardware when measuring with a VNA: there should clearly be both impedances with their relevant resonances, ideally symmetrically about the nominal center frequencies. Accomplishing all this with a simple feed plate, a single feed point and a single disturbance (the screw) is somewhat challenging and tough to replicate in a hardware duplicate. But with very tight manufactureing tolerances it IS possible over a very narrow frequency range (obviously). This is why it is so very difficult to copy mechanical drawings with good overall results. You really need to know what you are doing and also have the instrumentation. Pushing limits, I routinely measure ellipticity on HF in the confines of my small basement - figure that one out ;-)


    Once you have determined the apparent crossed polarized fields of your particular CP feed, you should be able to clearly affect each resonance individually (might take a piece of dielectric on a very thin dielectric probe). I usually use small pieces of PTFE, Rexolite, plastic or even just my finger tips for this type of work.


    After decades of work with CP polarization for a very wide range of applications and with quite a few years on HF too, last year I finally put together a (quadrature) dual channel polarimeter demonstrator for HF and this spring I also added a dual channel downconverter for 2.4 GHz for demonstration purposes:


    https://73.fi/oh2aue/oh2aue_polarimeter.htm


    Now, for my tripole antenna experiments I obviously need a three channel polarimeter. Think of this as an analogue oscilloscope CRT with magnetic deflection using external coils (e.g. Cossor 1039 or vintage radar CRT): instead of two orthogonal coil pair, only three deflection coils are needed in trigature, i.e. spaced at 120 degrees. Obviously magnetic deflection if bandwidth limited, but the display is on an arbitrary IF anyway. And I just love the dual time constant phosfors of my radar CRT :-)


    Until now I have been using vintage HP Vector and Constellation Displays with various homebrew 3 phase/2 phase RF transformers and matching three channel coherent converters depeding the on frequency band. This is all very fine for displaying CP ellipticity directly and in real time, but all the way, it is imperative to see also the complex impedances, such as (plot of the three resonances, 0 degrees and +-120 degrees with the total return loss of the trigature hybrid with imbalance load, 5dB/div):


    https://73.fi/oh2aue/2400_MHz_…rid_input_return_loss.jpg


    The overall ellipticity (linear deflection) of this contraption may be seen in the last plot of the first link.


    Michael, oh2aue


    P.S. winding of CRT deflection coils is described in detail in the Bell Labs microwave series... :-)


    P.P.S. how many multipole antennas can you count in the AO-40 photo on the left?

    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