| MMDVM MicroRepeater / Dual HotSpot hat for RPi
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Click here if you are interested in a more easy to build simplex HotSpot hat for RPi type B!
Version 1.0, released in September 2018, integrates an onboard SAW RX filter to improve isolation between RX and TX signal paths as well as increase resistance to strong out of band signals (close Radio or TV broadcasting transmitters) when connecting to a more serious antenna! Implemented SMD components (R, L, C) of size SMD "0603" with big enough pads for comfortable handsoldering or even accepting "0805" in a case of a necessity! Operates in UHF 70cm band only!
This page is about homebrewing an enhanced dual MMDVM HotSpot module for Raspberry Pi - type B.
The MMDVM dual HotSpot (MicroRepeater) board as shown on the photo above has been designed in an attempt to improve the receiver's characteristics of a duplex (dual) HotSpot "hat" built arround two ADF-7021 single chip transceivers and STM32F103 controller.
The board introduces an integrated receiving SAW bandpass filter centered at 432,92 MHz. The 432,92 MHz SAW filters have been originally designed to be used in low power devices which makes them affordable and widely available on the market. As per measured frequency response curve the usefull receiving bandpass frequency range extends over 7 to 8 MHz wide. At the same time, with a properly choosen TX / RX duplex frequency pair the isolation of the receiver from the transmitter's signal can be increased by well over 10 dB!
For further information and instructions on programming the neccessary firmware into the STM32F103 microcontroller, please visit the José Andrés, CA6JAU's GitHub page as well as his video (Tutorial instalación ZUMSpot Pi) at YouTube. The video is highly informational regarding the downloads, compilation, upload and installation of all the necessary software packages to the RPi and HotSpot board, including the MMDVM software, written by G4KLX . Use the "MMDVM_HS_dual_hat" settings in the board selection section of the "Config.h" file for proper firmware compilation.
|Bill of materials (15 kB - xlsx MS Excel)||PCB - Gerber files (63 kB - zip)|
|You can also order three high quality PCBs from OSH park prototyping service here!|
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