1. Building The AfriCUBE Transponder.
AMSAT SA SPACE SYMPOSIUM 2019
Author :Anton Janovsky ZR6AIC

2. AMSAT SA SPACE SYMPOSIUM 2019
AfriCube Hardware.
RX Bandpass filter (70cm / 144) 7 Stage
RX SDR 12Bit MSI Chipset.
Processor STM 32 ARM.
Local Oscillator Si570 (IIC)
Transmitter Texas Instruments IQ Modulator TRF3701.
Power AMP MMZ09332BT1 30DB Power AMP.
Power supply and Solar regulator. (5V only)
Estimated Power 2.5W total usage. When on full power.
Stanaby and telemetry only much less.
Space frame and Antennas.
AMSAT SA SPACE SYMPOSIUM 2019
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3. AMSAT SA SPACE SYMPOSIUM 2019
IQ transmitter board.
We wanted a SDR transmitter witch could be used for VHF, UHF and S band and that is easy to use with the standard SDR software applications.
My thinking was that I could possibly use a simple SDR chipset for RX and my IQ modulator board for TX.
I then developed an IQ Modulator board that could be plugged into an Orange Pi.
Why the Orange Pi? The Orange Pi is fast, small,low on power usage and the software is compatible with Linux witch makes it easy to develop the SDR software.
AMSAT SA SPACE SYMPOSIUM 2019
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4. AMSAT SA SPACE SYMPOSIUM 2019
The IQ modulator board.
The requirements that I wanted from the Board.
500mw up to 1W transmitting power. (+27dbm)
Proper output low pass filter 40db down at least.
Frequency must be programmable. (I2C controlling Local oscillator).
Narrow to 100khz bandwidth municipal modulation schemes.
Any modulation must be possible. (FM, AM, SSB, PSK, AFSK, SSTV, Row IQ )
It should be low power for the potential to be used on a Balloon flight or possibly on a Cubesat. (Max 2W power consumption for complete system).
The thinking was that a MSI SDR chipset can be used for RX and IQ Modulator board as TX.
This system should also be suitable to be used for ground station transmitter allowing for complex modulation schemes.
Modulation input must be from Standard Linux ALSA driver.
My selection of the Orange Pi zero as the controller board for driving the modulation audio and I2C controlling the Local Oscillator frequency.
Gnu Radio as an possible SDR chane.
C and Python Application for compleet system
AMSAT SA SPACE SYMPOSIUM 2019
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5. AMSAT SA SPACE SYMPOSIUM 2019
IQ Receiver Board .
We wanted an SDR front end at least 12Bit resolution.
The MSI chipset seems to be best fit
AMSAT SA SPACE SYMPOSIUM 2019
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6. AMSAT SA SPACE SYMPOSIUM 2019
Block Diagram of software chain
AMSAT SA SPACE SYMPOSIUM 2019
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7. AMSAT SA SPACE SYMPOSIUM 2019
Transmitting data flow.
How does this board work?
I have the Orange Pi connector on the left witch has an additional USB and Audio in and out ports not normally available on Raspberry Pi. I selected the the IQ modulation chip TRF3701 based on low power and simple configuration and has a 0dBm RF output drive. I now needed a programmable oscillator and decided on the Si570 but it is using a bit more power as what I would have liked. This device frequency can be programmed via the I2C bus. The last step was to amplify the IQ modulated RF signal to about 500mW and add a low pass filter on the output. We am using discrete components for the low pass filter so that it could be change for different frequency. The design was so that the board filter can be build for 145Mhz(2M) ,435Mhz(70cM) and 1.2GHZ. There is unfortunately also a rf Z matching circuit on the Power amp witch will also need to be changed for the different bands. I was looking for about 30 db gain and decided on the MMZ09332BT1 witch should give me the correct amount of power. This device is also power hungry but small in size and I had a bit of a space problem.
AMSAT SA SPACE SYMPOSIUM 2019

8. AMSAT SA SPACE SYMPOSIUM 2019
IQ transmitter board.
The challenges
I needed to develop a possible transponder and telemetry system using less that 2W total power usage.
I originally intended to add Real time clock and Power monitoring circuit on the same board but it was impossible to fit it all on this small board.
As I have very limited space on the board to make it fit on the same footprint of the Orange Pi Zero it was a bit of a challenge.Here is the Diagram of the Hardware V1.4.
AMSAT SA SPACE SYMPOSIUM 2019
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9. AMSAT SA SPACE SYMPOSIUM 2019
Software for the Transmitter.
I am planning to use the MSI_SDR libraries to read MSI SDR IQ input from rMSI-SDR and then manipulate the IQ signals using csdr libraries to do some re sampling and Mixing of IQ signals from a second IQ source generated from a CW and Direwolf ax25 (APRS) telemetry audio signal.
The plan is to use PSK for AX25 1k2 and 10 word per minute for CW.
AMSAT SA SPACE SYMPOSIUM 2019
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10. AMSAT SA SPACE SYMPOSIUM 2019
Software steps.
Take IQ stream from MS_sdr at 720KHZ sampling and then disseminate to 100KHZ and applying 100khs low pass filter then mix Telemetry Audio IQ file and send to Alsa Audio Device.
Then create CW Audio from CW application and then use sox to convert audio file csdr. (ZR6AIC balloon experiment 27c 12.5V ON)
Then convert CW audio to PSK IQ file.
Create ax25 Audio message from Direwolf with temperature , RF TX power RF RX ALC and battery power levels. (ZR6AIC Balloon Experiment Transponder #ON,50,27,12.5,300,) #Cpu Temp,Inside Temp,Battery Voltage,Transponder power mw.
Create a cron to generate CW and Direwolf audio files Every 3Minutes
Create a cron every 1 minute and script to monitor ALC and Transmitter power and adjust alc and TX power.
Create startup script to start rtl_sdr IQ stream and mix Telemetry Audio IQ stream and send it to Alsa audio Device.
Create Initialization script to set Transmitter frequency by sending I2C data to I535 Local oscillator.
Read RF power level on RF power amp by Reading I2C A/D converter.
Adjust IQ Audio Level by adjusting Csdr multiply function constant (ALC) to adjust PSK divination.
AMSAT SA SPACE SYMPOSIUM 2019
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11. Demo of Live Transponder using Software chane.
Lime mini Pi
Mhz TX
435.3Mhz RX
Mhz TX
Mhz TX
10mw Tranmitter
AMSAT SA SPACE SYMPOSIUM 2019

12. AMSAT SA SPACE SYMPOSIUM 2019
Video of Live Transponder
AMSAT SA SPACE SYMPOSIUM 2019

13. AMSAT SA SPACE SYMPOSIUM 2019
Questions ?
AMSAT SA SPACE SYMPOSIUM 2019