QO-100 the first geostationary amateur radio transponder
German version of this article here / deutsche Version des Artikels hier
Above all, this article should present a systematic overview of the topic, please accommodate individual projects in other articles or in the forum. This is the first english version, a raw google-translation - be patient.
Due to favorable circumstances (a high-ranking politician of the state of Qatar is a radio amateur), the TV satellite Es'Hail-2 also houses a small amateur radio payload. The satellite, including the ham transponder, was built by Mitsubishi in Japan and transported by SpaceX to its geostationary position in November 2018, about three diameters of earth perpendicular to the equator. Since February 2019 the amateur radio transponder can be used. Wikipedia article
- 1 First steps via web radio
- 2 Narrowband Receiving
- 3 Narrowband Transmitter
- 4 Broadband Reception (Digital TV)
- 5 Broadband Transmitter
- 6 Links
First steps via web radio
For the reception a usual satellite dish is suitable. A diameter of 60cm is sufficient, but 80-90cm offer more reserve. More exotic antenna shapes such as horn antennas would also be conceivable. As usual, a LNB (low-noise block) is attached to the dish. To the LNB below more.
A larger diameter does not give much to the reception, the signal-to-noise curve soon turns asymptotically into a horizontal plane It looks different for the transmitter, here replaced a larger diameter missing transmission power. Simply obtainable are still offset dishes up to 2.40 m diameter. Example: OP240L consisting of two half-shells with 1.20 * 2.40 m The transport should not be quite cheap. Compared to 125cm, the gain is 6.3dB higher, corresponding to a four times higher transmit power - with smaller aperture angle and higher mounting and alignment requirements.
It is also possible to use the same dish for transmission, with several "dual-band" antenna feeds available, see below. Due to the lower transmission frequency, the alignment is easier, the opening angle is larger.
Aligning the antenna
The antenna direction and rotation of the LNB (a few degrees different from the vertical mounting!) For your own location can be calculated here:
Satlex.de calculator for azimuth and elevation angle for 26 ° East
(Here is an older TV satellite "Badr" registered in the same position). The required accuracy depends on the dish diameter. A cheap "satellite finder" does not help, since the reception field strength is much lower than e.g. from Astra 19.2 ° East. An RTL-SDR can display the broadband beacon in the spectrum, so that the antenna can be aligned to maximum.
To determine the horizontal direction, one can use a compass, which is, however, influenced by metal parts in the immediate vicinity. More specifically, a satellite image of the location of Google Earth, on which one seeks highly visible targets in the satellite direction, trees, chimneys or the like. A scale is often attached to the dish mount for vertical alignment, which is divided very roughly. In addition, the antenna mount must be exactly vertical, which is checked with a spirit level. It is also possible to aim at a well-known TV satellite and then try to turn the dish around the difference angle. And of course there are apps for the smartphone.
Because of the different polarizations of QO-100 for the two signal directions here are some general remarks: The choice of polarization has more practical reasons than physical ones. For the VHF / UHF mobile radio, a vertical omnidirectional rod antenna is common, while for long-distance traffic horizontally polarized long yagi antennas are used. On shortwave you can choose from steep or shallow radiation, depending on the distance.
Of particular importance is the polarization for the Earth-Moon-Earth route, since physical phenomena lead to polarization rotations, and a few tenths of a dB difference can decide on success or failure.
In the mid-seventies "UKW-Berichte / VHF communications" magazine offered a switch-box for crossed yagi antennas, which had in addition to the 4 usual polarizations another two linear 45 degrees inclined positions. One could easily find out the currently most favorable polarization. Some articles in german by Terry Bittan DJ0BQ UKW-Berichte 3/1973 and 1974 and 1975 , here the schematic for 6 positions, see "Bild 8".
For the connection to QO-100 the space requirement of the antenna at the satellite could have played a role. The circular polarization towards the satellite causes the location on the earth to make no difference. For the linear polarization of the route to earth, however, the LNB must be mounted rotated differently depending on the location.
The decisive factor is that the polarization is chosen to be the same on both sides. No matter which one you take: This is optimal, one ("orthogonal" to optimum) has very high losses, depending on the propagation conditions. All other polarizations have a loss (close to the noise level) of up to 3 dB (half power).
A linearly polarized WiFi antenna is thus not the optimal solution as a transmitting antenna, a circular antenna of the correct direction of rotation is the better solution, therefore the following paragraph:
Dual-band Antenna Feed
It is important that the receiver is not disturbed or even damaged by the transmission signal. Above all, the transmitter output should suppress the four- and five-fold frequency (9.6 / 12 GHz) with a low-pass, since these fall in the reception range of the LNB. The beam has to agree approximately. In addition, you have to comply with the different polarizations, to send always RHCP (right-hand-circular-polarized), which turns by the mirroring on the dish, that is, the food antenna must be LHCP. To receive vertically for the narrowband range and horizontally for the broadband range. The latter can be switched in the LNB on the operating voltage, 18V = H 14V = V, (Merkreg "H" higher voltage = "H" orizontal) If you do not have the 18V (broadband reception only), you can also rotate the LNB by 90 degrees , then both polarization planes interchange.
Two horns coaxial:
Dual-Feedhorn from OM6AA from Prague - manufacturer
The coaxial cables are each different by lambda / 4 (for 13cm wavelength times shortening factor, this is about 22-25 mm difference).
The Power Divider is a commercially manufactured part of e-meca.com
Two types of cable were tested:
LMR195 (reduction factor 80%) and SM141FEP (Shortening Factor 71%)
Horn for 3cm and patch for 13cm:
construction proposal by DJ7GP - manufacturer]
"POTY" (Patch Of The Year) G0MJW, PA3FYM, M0EYT dualband feed comparison / - Supplements to this from HB9PZK - PE1CKK kit
LNB (horn) for 3cm and helix antenna for 13cm:
On the pictures you can see the correct winding sense of the helix for QO-100 "LHCP".
A long helical antenna without a dish must be wound in opposite directions. The polarization is not switchable. But you have (as well as the patch antenna) a single feed without power divider. A crossed yagi or the above-mentioned double horn has two to four feed points, which are fed by power dividers and cable pieces of different lengths.
construction proposal Günter DF2GB
construction proposal of Rainer DM2CMB in the TV Amateur Nr 194 p.5-8 (currently not on the web)
In the AMSAT forum you can find more examples.
Older dielectric resonator LNBs are not suitable for QO-100 due to excessive drift. Unfortunately, the manufacturers do not write that in the specifications. Therefore, there are some lists of PLL LNBs, but different hardware can be offered under the same order number, there is no guarantee for this:
UHF-Satcom PJM, southern GB
Again, the necessary accuracy on the high reception frequency is more critical than the transmitter. This is especially true for the narrow band range. An SSB signal that runs away constantly is no pleasure. A drift of 100 Hz during a radio conversation is still tolerable. In terms of 10 GHz, this amounts to 0.01 ppm (parts-per-million) or the eighth point, which is not sustainable for conventional quartz oscillators.
There are four options:
- Temperature compensated crystal oscillator (TCXO),
- Heated quartz oscillator (OCXO oven controlled crystal oscillator)
- GPS-adjusted crystal oscillator (GPSDO GPS-disciplined oscillator)
- Rubidium frequency standard
For the reception, there is still the possibility to constantly readjust the receiver by controlling the beacon, so far existing solutions:
- Windows Software SDR Console by Simon G4ELI
The idea for drift compensation came from Moe Wheatley AE4JY back then for the AO-40.
Simon asks before downloading a donation for dog food now or tomorrow or sometime ...
- Raspi software Satcontrol by Frank DL3DCW with GQRX and two RTL SDR sticks
However, the drift between the two RTL SDR can not be corrected.
Reception with RTL-SDR
The cheapest receivers are USB sticks for DVB-T or DAB in conjunction with a PC or the Raspberry Pi
A "luxury version" from rtl-sdr.com with TCXO and shielding metal case
There are also cheaper Chinese replicas, but the shielding is bad, the case is not well contacted. The RTL-SDR also has the advantage that you can choose the reception frequency in a wide range. You do not need a LNB recycler in an amateur band to use an SSB transceiver.
There are some welcome programs for Windows:
- SDR-Console - as recommended above especially recommended for drift compensation
and many more, a link list on rtl-sdr.com states the following:
- SDR # (or SDR-sharp)
- Linrad (Windows / Linux / Mac)
- CubicSDR (Windows / Linux / Mac)
- OpenWebRX (Python Based)
- QtRadio (Windows / Linux)
- Multimode (GNU Radio)
- QIRX SDR
Software for Linux, Mac, Raspi, Android:
- GQ-RX - tutorial on this based on GNU Radio
- WebRadio (Linux)
- Sdrangelove (Linux)
- Natpos (Linux)
- ShinySDR (web interface, runs on Mac, Linux, Raspi ...)
- RFAnalyzer (Android)
- Kukuruku (browser based)
also listed: some payment programs with free trial versions and special programs.
In this list SDRangel for Windows und Linux is missing:
"SDR Rx/Tx software for Airspy, Airspy HF+, BladeRF, HackRF, LimeSDR, PlutoSDR, RTL-SDR, SDRplay RSP1 and FunCube"
just an idea ...
The pure duration of the signal over 2 * 38000 km causes a delay of about a quarter of a second. In addition, there are delays, especially due to digital filters, and for a webradio as well its processing time and the runtime through the web.
For telephone signals one uses for a long time a so-called echo cancellation, in order to suppress disturbing echo. For QO-100 could be similar attempt to subtract the microphone signal at runtime delayed from the received signal amplitude and phase correct. You could hear interjections aloud, while your own broadcast, which rather disturbs, would be quieter. However, since the SSB signal would have to be set exactly to beat zero, only a DSP using "adaptive filter" could use the delayed signal as a pattern function. Simple solutions with analog technology are overwhelmed here.
In the narrow band, all common amateur radio modes are allowed up to 2700 Hz bandwidth, i.e. SSB, CW and digital modes. Bandplan here divided into CW / narrow Digimodes up to 500Hz / Digimodes / mixed modes / SSB only. FM is not allowed because it's too wide-band. There are several possibilities for generating these modulations in the 13cm band:
- classic SSB radio and transverter
- Processing of analog or digital modulation to I/Q signal and upmixing with an I/Q modulator
or special hardware like
- Lime-SDR 100 kHz to 3.8 GHz
- Red Pitaya 125 MS / s, (additional transverter required)
- Adalm-Pluto 325 MHz to 3.8 GHz
- HackRF one 1 MHz to 6 GHz
- BladeRF 47 MHz to 6 GHz
etc. which already contain a high frequency generation
For SSB generation there are three classical methods:
- Filter method (one mixer)
- Phasing method (two mixers, also included, for example, in an I/Q modulator IC)
- "third method" according to Weaver (four mixers)
A higher starting frequency is better because the filters for suppressing the oscillator and mirror frequencies are less critical. So use rather 70cm than 2m or shortwave.
Suppliers for off-the-shelf transverters are listed below in the list of 13cm stations:
There are also some building proposals or kits.
Holger Eckardt DF2FQ has published an interesting converter in "Funkamateur" 9/2019. By applying the phasing method of conversion, it also achieves good rejection of LO and image frequency on a tiny board, even from the 2m (or 10m) band. In the table of contents of the magazine a photo of the board (middle first page) is displayed.
The circuit consists of a typical I/Q modulator IC ADRF6703 with two mixers, LO phase shifter and PLL VCO. Controlled with a PIC12F629 and 26 MHz TCXO. Tunable via serial interface in 1 MHz steps. Its input is fed by the second phase shifter, depending on the equipment for a 2m or 10m SSB signal, a double-T LC filter. The only filtering action on the output is a Murata SAW filter SF2173E. Noise suppression for 2m 60 dB, for 10m still 47 dB. Output power 50mW at 38 dB two-tone IM distance. If there is a lot of demand, he wants to put on printed circuit boards.
Broadband Reception (Digital TV)
A special receiver for amateur TV only with a NIM satellite tuner Serit FTS-4334L - Serit_tuner wiki page from BATC, whose receive data are displayed via USB connection in the PC under Windows. Many other measurement options besides normal reception and an adjustable sample rate down to 88 kS / s are currently not available in any other receiver.
The Minitiouner does not yet provide a 14 / 18V switch for polarizing the LNB, and does not include a digital switch to DiSEqC protocol as provided by regular satellite tuners.
Parts kits are sold for tax reasons only to BATC members, the "cyber membership" with e-mail-related club magazine costs 8 pounds per annum (see below).
The French amateur radio club REF also offers two parts, but currently sold out:
- Minitiouner Pro incl. tuner ("Pro" = 2 receive channels via separate USB ports, 18V DC / DC converter and DiSEqC feed with RT5047 to the LNB, optional I2C display port, all included in enhanced MiniTioune software) 109, 50 € - docu (in French)
- Serit-NIM-Tuner FTS-4334L single 35,00 €
Some screenshots of the software at 88kS/s. Lower bandwidth significantly reduces the effort required for transmission power and dish size. As you can see, however, a good resolution is still achievable. Maximum bandwidth (4 MHz) and the 120 kHz (factor 33) used here theoretically make 15.2 dB difference in requirements. Instead of 100 W and 2.4 m, then e.g. 10 W (-10 dB) and about 1.2m (-6dB) are sufficient.
TV satellite receiver
Most satellite receivers can not handle the low bitrates of QO-100, but there are exceptions.
The reception range of most satellite receivers begins too high for direct reception to set QO-100. Here you can trick with some types, e.g. by entering a wrong LO frequency.
OCTAGON SF8008 instructions for the QO-100 reception (german)
Another solution to the frequency problem is a RX-converter here to simultaneously translate the wideband range to 1340 MHz and the narrow band range 144 MHz.
Raspberry Pi as Digital Video Modulator
As part of the Portsdown project (see below) there is a software RPI-DATV for the Raspberry Pi, which directly provides the (digital) I/Q baseband signal for DVB-S from two GPIO outputs. A bitrate-dependent low-pass filtering in front of the modulator is therefore necessary. Input is either a Raspi camera or a video digitizer on the USB port. For testing purposes, there is even a direct output of a complete transmission signal in the 70 cm band, the so-called "ugly" mode. One only has to connect a piece of wire as the transmitting antenna to a GPIO pin, and the signal may be received e.g. with the Minitiouner. Operation via touchscreen on the Raspi. A pre-programmed SD card can be found in the BATC shop . For tax reasons, you have to become a member of the BATC, one year (from Germany) costs 8 or 30 pounds (CQ-TV magazine subscription by e-mail or printed)
The software on Github
Wiki of the BATC
In order to convert an I/Q baseband signal to 2.4 GHz (or to generate SSB there directly after the phase method), there have been complete I/Q modulator ICs for around 20 years, mainly from Analog Devices.
A circuit with AD8346 from the year 2002, in german, see chapter 6
Table: Analog Devices I/Q modulators, 13 types are usable for 2.4 GHz
The Portsdown Project
A British project around the Raspberry Pi: a transmitter for digital amateur television, not only via QO-100, but also terrestrial. There are two versions, "2018" was still built with a specially designed transmitter, "2019" uses a "Lime-SDR mini".
The sample rates range from 88 kS / s to 4 MS / s, proportionally increasing the power required to reach QO-100. For the maximum, a 100W transmitter with a 2.40m dish is recommended.
The DATV Express project
similar to Portsdown but a Windows PC instead of Raspi
it supports different transmitter (and receiver) hardware:
- DATV Express hardware Tx board
- LimeSDR-USB Tx / Rx board from Lime Micro
- LimeSDR mini Tx / Rx board from Lime Micro
- PLUTO-ADALM Tx / Rx board from Analog Devices
Transmitter Output Stage
There are just a few amateur power amplifiers for the 13cm band available:
Discussion in AMSAT forum
20 Watt PA by Rene PE1CMO - Datasheet of the dual transistor BLM2425M7S60P used here
20 Watt PA by Hristiyan LZ5HP from Sofia, Bulgaria also an Ampleon transistor according to DL7UKM BLP9G0722-20G
20 Watt PA by Fred F6BVA, only building proposal - Datasheet of the MW7IC2725 used here
10W-PA by Michael Kuhne DB6NT and complete converter with 20W
13cm-PAs 0.9W from Ewald DK2DB (selling-off) - the transistors FLU10 are no longer manufactured
13cm-PAs by Dirk Fischer DK2FD - and a narrow band converter for QO-100 for a 2m or 70cm SSB TX
There are also Wi-Fi power amplifiers from China, but customs often confiscate them because they are not allowed here for Wi-Fi. When ordering, therefore, demand that "ham radio" or similar be written on the label.