The Funcube Dongle Pro (FCDP) is a small USB-key-sized low-bandwidth SDR.
It uses an audio codec as ADC (like many amateur radio projects) and thus can only be used for narrow-band signals up to 80kHz.
However, for capturing a single TETRA channel, those 80kHz is actually more than sufficient.
It is generally available for purchase from http://www.funcubedongle.com/ - however, it is out of stock almost all the time and you will have to click the order button at exactly the right time in order to get one. Apparently it is impossible for the manufacturer to keep up with the demand.
The FCDP hardware seems to be using the following components:
- Microchip PIC24FJ32GB002
- 16-bit low power microcontroller with Full-Speed USB, 32 KB Flash memory, 8 KB RAM, and advanced peripherals, 28-pin package
- homepage: http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en536120
- datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/39940d.pdf
- TI TLV320AIC3104 Low-Power Stereo CODEC with 6 Inputs, 6 Outputs, HP Amp and Enhanced Digital Effects
- Elonics E4000 Zero-IF Low Power CMOS Multiband Tuner (64 to 1700 MHz)
- homepage: http://www.elonics.com/products/rf_tuners.do?id=1
- product brief: http://www.elonics.com/assets/PB_E4000_10_2009.pdf
The hardware architecture therefore is quite simple:
The PIC24F implements the USB protocol/interfaces for HID (tuning) and audio towards the PC. It also drives the TI codec and the Elonics silicon tuner via an I2C interface.
Analog RF data enters the Elonics silicon tuner, where it undergoes zero-if down-conversion to complex I/Q baseband, which enters the TI audio codec where it is digitized using left/right channels for i/q. The resulting digital audio stream is passed to the PIC24F, which forwards it via USB to the host PC.
The OsmocomTETRA repository contains a demodulator script called fcdp-tetra_demod.py that can be used with the FCDP. You have to use the 'qthid' application provided with the FCDP in order to tune to the respective tetra carrier frequency.