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.