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Approach E2.11 – Portable UHF Open Repeater Sponsored by: Texas State University Logan Young, John Halliday, Charles Hinkle, Christopher Schneider Power Management/Enclosure Project Overview Results Background Info Acknowledgements Software: Microprocessor Programming Software, CHIRP/Radio Programming Project Manager, PCB Design Team Members Repeater Controller The repeater controller was developed with two main priorities in mind. The first priority being forwarding the incoming signal from the receiving radio to the transmitting radio. The second priority being programming the radios to desired receiving and transmitting frequencies using the desired CTCSS (Continuous Tone Coded Squelch System) frequencies. SVXLink is open-source software that has many functions built-in focused on HAM radio repeater operations, including making a repeater controller. CHIRP is also open-source software that allow HAM radio users to program many makes and models of personal HAM radios. The Raspberry Pi 3 microprocessor is a small, cheap computer that has a Linux-based operating system, a large and active user community, and a variety of interfacing options. The Raspberry Pi 3, along with the previously mentioned software packages, makes up the bulk of the repeater controller used in the portable repeater. Radio Interface Board The repeater controller requires both analog and digital signals to transfer to and from the radios. This creates the issue of grounding loops if the radios are connected directly to the repeater controller. The radio interface board was designed to isolate the radios from the repeater controller to prevent grounding loops using transformers and an opto-isolator is a configuration based off the popular Easy-Digi isolation. This allows for the repeater controller and radios to exchange analog signals, which is all that is needed for the repeater functionality, but digital connection is still need for the repeater controller to program the radios. The audio jacks on the radios are used both for radio functionality, and programming. Therefore the radio interface board required digital buses from the radios to the repeater controller, which is used to program the radios when the repeater program isn't running. User Interface The user-interface was developed with simplicity of use in mind. The Raspberry Pi 3 runs an Apache web server that serves a few web-pages written in HTML, CSS, JavaScript, and PHP which are displayed on a small touch screen. These pages allow a user to start the repeater, stop the repeater, and select the operating frequencies of the repeater along with the CTCSS frequency. Power Many of the components in this system had various power requirements and in order to make the repeater portable, 12V batteries were provided by the sponsor. To operate the Raspberry Pi, a 5V voltage regulator was necessary to utilize the provided 12V batteries. For the radios, battery eliminators were attached to the HT’s. Faculty Sponsor/Advisor: Dr. Stapleton Mentors: Dr. Stapleton, Dr. Compeau, Dr. Talley Instructor: Dr. Compeau KF5INZ, The Open Repeater Project The goal of the project was to design and build a UHF Duplex Repeater that would be portable and operate without an electrical grid, intended for emergencies and for special events. The repeater would need to be low cost, transmit a minimum of two miles, and be weather proof. The finished repeater will include the antenna, antenna mast, and a weather-resistant container that houses all the electronic components and the GUI. Amateur radio operators (AKA Hams) are hobbyists that use a spectrum of radio frequencies for the non-commercial exchange of messages. There has been a recent surge of hams in the United States following the decision to remove a licensing requirement to learn Morse code. Currently there are over 4 million amateur radio operators in the world and over 750,000 in the United Sates. In Texas alone, there are 52,500 licensed hams and growing. Repeaters are designed to listen and transmit on the inverse radio frequencies that a ham’s mobile transmitter uses. This is done to increase the range of the transmission to other Ham's tuned into those same frequencies. The OpenRepeater project was designed to create an open source, low cost, low power and modular repeater. The finalized system consists of a portable repeater powered by a 12V battery, allowing operation for up to 9 hours while maintaining portability. The repeater program is fully functional allowing the user to change frequencies and CTCSS via a 5” display screen. Additionally, a radio interface board was designed to incorporate the signal isolation necessary when handling audio and data through the same system. This board also simplifies the assembly of the repeater by including the appropriate connectors to both the radios and the Raspberry Pi. Following a considerable project scope redefinition last semester, this team has been able to efficiently allocate the time and resources necessary to provide the proper system requested. Between both teams, this project has proved to be a highly multidisciplinary undertaking, requiring various degrees of research across a broad spectrum of engineering disciplines. Additionally, the amount of collaboration required with Team Zelda truly emphasized the importance of communication and clarity in determining how to approach each challenge and divide the individual components so that the overall system is developed as efficiently as possible. In conclusion, this project has been integral to not only showcasing the knowledge and skills proficiency in RF techniques and the art of amateur radio in order to better appreciate the application of electrical engineering foundations. Discussions/Conclusions Raspberry Pi Filter Cavity and Antenna Power Supply Voltage Regulator Radio Interface Board Receiving Radio Serial to USB & Isolator (2) USB Soundcard Transmitting Radio Voltage Sensor Display DATA POWER AUDIO Repeater Controller and Power Block Diagram AC Charging Software Level Block Diagram Apache Webserver GUI CHIRP SVXlink CTCSS Originally, it was intended that the CTCSS signal would be detected by the SVXLink software. After testing it was found that the software was unable to detect a CTCSS signal as it was received by the repeater controller. At the same time a CHIRP command-line interface was found allowing for the systematic programming of the transmitting and receiving radios. This meant that the radios could be used to detect and transmit CTCSS signals. After consideration, the project design was altered, incorporating the CHIRP command-line interface. Radio Data Transfer In order to incorporate the CHIRP command-line interface data needed to be exchanged between the repeater controller and the receiving and transmitting radios. Data wires were added to the radio interface board to meet this need and a push-to-talk (PTT) problem was created. The PTT signal from the repeater controller tells the transmitting radio when to transmit the signal it receives. The new data lines interfered with this signal, making the repeater inoperable. This issue was resolved by controlling the connection of the data lines using transistors controlled by the repeater controller. Remediations Test Cases Specification Result Compliance PCB Design Signal Accuracy Accurate TX/RX Compliant System Enclosure IP53 Weather Resistance Success Compliant Battery Operation Operational Lifetime 6+ Hours Compliant Open Repeater Software System Reliability 100+ Message Traffic Compliant User Interface Time from Login to Main Screen 27 Seconds Compliant PCB Design System Overview
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