rru-rf-hw

Remote Radio Unit RF board.

What is it?

An FM repeater in a milled aluminum chassis. Built around a pair of CC1200 chips from Texas Instruments and an RF power amplifier module. Revision A with CC1200 RF front-ends supports various FM-based modes, including M17 and AFSK.

Quick fact sheet

RF power module - RA60H3847M1
RF output power - 1..60W continuous, up to 80W with lower duty cycle
Frequency range - 420..450MHz
Frequency error - <0.5 ppm over -40 to +85°C range
Supply voltage - 13.8V DC
Power consumption - <150W at 60W RF out
Load mismatch immunity - continuous over the whole VSWR range (built in RF isolator)
Harmonic content - 2nd <-40dBc, 3rd <-55dBc (435MHz at 48.3dBm)
Mode support: analog FM, M17, (A)FSK
Circulator: WH3538X-1, 400..470MHz (microstrip)
Dummy load: Anaren J100N50X4B

Firmware

A basic, "crash-test" frmware template is available here.

Flashing the MCU over UART

• Build the firmware using CubeIDE
• Copy the .bin file over to Raspberry Pi
• Run stm32flash -v -R -i "-539&-529&539,529,:-539,-529,529" -w rru-rf-fw.bin /dev/ttyAMA0

In case of problems, see this for some additional explanation.

Chassis

Milled aluminum chassis is required. A reference design can be obtained from a separate repository.

Revision history

Revision A

Initial revision.

Revision B

• Switched mode voltage regulators have been replaced with linear.
• Added a buffer between the 40 MHz reference TCXO and transceiver ICs.
• Added bleeder resistors at the RF PA and 13.8V power supply.
• Slightly improved ALC circuit.
• Reduced N-connector cutouts (4.5mm down to 2mm).
• Added decoupling capacitor arrays at both RF PA's supply and VGG pins.
• DA15 connector now has MCU's BOOT0 signal available at pin 13.
• Bodge wire mod is no longer required, as both baseband trigger signals are now routed to the MCU.

Revision C

• Added a lowpass filter after the RF PA stage
• Added a bandpass filter at the RF input
• TX and RX blocks are now clocked independently
• Pull-down resistor at TP2 (BOOT1)

License

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.