Beiträge von DL3DCW

    I focus on the Raspberry Pi because I use it myself and there are currently no easy-to-use solutions. For me it's great that this little system runs completely independently of my main computer and controls my entire QO-100 station. That's my main motivation.

    In addition, the memory card images and the same hardware make it easy for me and the users to get a running system without major problems. If someone wants to adopt the approach to other systems, you are welcome to do this. I have not planned this. Because I'am very happy with my Raspberry.

    Note: All you need (source code etc.) you can find on raspberry pi image. But do not expect too much. I'm a bad programmer. Most important for me is that it works ;-)

    I calibrate my RX system to CW beacon 10.489.550.000 Hz (zero beat). For me it doesn't really matter if this is the perfect and "true" frequency or not. After that I calibrate my TX offset. Then I am ready to have fun ;-)

    But I have noticed that the engineering beacons of the different satellites are not always perfectly on the specified frequency. They vary in all directions. Who is right?

    After I have calibrate CW beacon to 10.489.550.000 Hz the PSK beacon is exactly on 10.489.800.000 Hz. Thats all I need.

    SAT Controller SDR Nano - CAT interface

    For connecting FT-817 (CAT/ACC socket) you can use USB/TTL converter below (CP2102). Very nice: All handshake signals are available. It also works fine as PTT output from a seperate digimode computer. For this only one external diode in series is required to connect DTR signal to PTT input (DATA socket) of FT-817.

    SAT Controller SDR Nano - Troubleshooting

    1. Decompressing .zip file fails

    Please use an other unzip tool. Some programs have problems with big file size.

    2. Wrong locale, timezone, keyboard, WiFi settings

    Adjust localisation settings (Preferences/Raspberry Pi Configuration/Localisation).

    3. Warning "Crash detected" at SDR Receiver (GQRX) start

    You can ignore this message. It takes no effect.

    4. Warning "No connection" at SAT Controller start

    Please start SDR Receiver (GQRX) before you start SAT Controller and/or enable remote control interface in GQRX (Tools/remote control).

    5. Value “RX ERR” jumps or frozen

    Switch off “Drift correction” and repeat “Lock” procedure. If this takes no effect restart program and/or reboot raspberry because this function is not perfect at the moment. You also should experiment with the "Master" parameters. The defaults are set to Es'hail-1 beacon because this will work fine in most cases.

    6. Control transmitter (FT-817)

    Via USB/TTL converter (like CP2102) you can control transmitter (FT-817). For this connect RXD/TXD signals crossover and PTT GND output from CAT/ACC socket to DCD input of USB/TTL converter.

    7. Control up-converter (MKU2424)

    Via USB/RS232 converter (like FTDI) you can control up-converter (MKU2424). For this connect RXD/TXD signals crossover and DTR output from USB/RS232 converter via external NPN transistor to PTT input of up-converter.

    8. Transmitter (FT-817) can not be switched on

    Please close "SAT Controller", switch on transmitter (FT-817) and then restart "SAT Controller".

    9. Audio volume during own transmission

    TX audio volume can be set independent from RX audio volume. This is useful for avoid echoes via the transponder. You can adjust TX audio volume via the volume slider during own transmission.

    10. USB sockets occupied

    In some cases all USB sockets may be occupied with SDR sticks and USB converters. Additional mouse and/or keyboard you can also connect via Bluetooth. Then you don't need an external USB Hub.

    11. Operating digimodes

    The easiest way for digimodes is a seperate computer. For RX you can use the audio output from Raspberry and for TX the DATA socket of FT-817. For this connect DATA IN and PTT to the transmitting computer. In the future there will be a solution to operate digimodes directly from the Raspberry.

    12. Touch-only operation

    Touch-only operation will be optimized in the future. At the moment a mouse with mouse wheel is useful. For normal operation no keyboard is required. In some cases you can use the software keyboard (Accessories/Keyboard) or remote control via VNC from a desktop computer.

    Will be continued ... ;-)

    Next step is to make a PCB for raspberry touchscreen case. So it is easyer to copy. Maybe the AMSAT would like to distribute them if there is any significant demand ... ;-)

    SAT Controller SDR Nano

    With the "SAT Controller SDR Nano" a simple NB station for QO-100 can be realized. The software image include current Raspberry Pi operating system (Raspbian Stretch with desktop), a preinstalled SDR receiver (GQRX) and a control software.

    Image 1: Block diagram (with additional SDR stick for software drift correction)

    Image 2: Main screen (GQRX and SAT Controller SDR Nano)

    Image 3: Lock to master signal (Es'hail-1 beacon, default setting)

    As transmitter a FT-817 (via USB/TTL converter like CP2102) and a up-converter MKU2424 (via USB/RS232 converter like FTDI) can be connected. PTT input (from the transmitter) and output (to the up-converter) is possible via the handshake lines. For this the up-converter requires an additional transistor. Receive only operation is also supported.

    The image runs at Raspberry Pi 3B+ with the official 7" touch display of the foundation. Other displays/monitors are possible (maybe some adjustments are needed). For the two receivers (GQRX + drift correction) SDR sticks with rtl-sdr support can be used. Myself prefer NooElec NESDR Nano3 with 0.5 ppm TCXO because they fit perfectly to the small Raspberry.

    Some things should be noted before operation:

    1. Lock to master signal

    First, the system must be set to a reference signal (menu item "Lock", right mouse button). This is used to calculate the actual LO frequency and as master signal for the software drift correction. Default setting is beacon of Es'hail-1 (menu item "Master"). With the preset RF frequency you have to adjust the peak in the audio spectrum to 1.5 kHz.

    This process must be repeated occasionally if the LO frequency has drifted too far away. If you have problems, you should experiment with the parameters and possibly restart the program (unfortunately this function is not perfect at the moment).

    2. Adjust beacon frequency

    Fast fine adjustment is possible with a beacon signal in NB passband (button "Adjust"). Default setting is CW beacon of QO-100 transponder (menu item "Beacon"). With the preset RF frequency you have to adjust the peak in the audio spectrum to 1.5 kHz.

    This procedure should be performed before each operation (after a short warm-up phase). Because the SDR software sometimes shows errors of some 100Hz. This often happens when you restart GQRX, change frequency ranges or if you tune via the big frequency indication digits. For tuning it will be better to use the mouse wheel and/or place mouse pointer to desired frequency in the waterfall. The fine adjustment should be checked regularly. In the future hopefully this step can be omitted.

    3. TX offset

    Now the TX offset should be set (menu item "Offsets"). Alternatively, the offset can also be adjusted via a frequency tuning on the SDR or on the transmitter (previously unlock tuning knob) during transmission. For this the "Auto tracking" function have to be activated.

    The remaining functions hopefully are self-explanatory. But please note: The basic functions are given, but there are still errors. Because it's just a quick, stupid and dirty solution (I am only a little hobbyist and not an engineer).

    Important: The respective license terms apply. All the software comes without any warranty and without special support.

    Frank, DL3DCW