QRP Labs U4B Ultimate4, Operating Manual

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1. Introduction
The U4B tracker was developed over a period of 7 years from 2015 to 2022, in collaboration with
Dave VE3KCL who has launched 83 test flights from Toronto, Canada. With flight duration from 2
hours to 305 days (10 months, almost 17 laps around planet Earth), they all taught us something
and were great fun.
U4B is designed to be an easy to use, lightweight, low-cost module that can be configured as
simply as entering your callsign, yet for more advanced owners can be flexibly extended with more
sensors and as much complexity as you like. Automated tracking maps and utilities are available
on the QRP Labs website, both for simple tracking purposes and downloading your own telemetry.
The U4B PCB contains:
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33.0 x 12.7mm PCB (plus removable protrusion with micro-USB connector)
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Weight: 1.8g (with micro-USB protrusion removed)
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32-bit ARM microcontroller running QDOS ( Q RP Labs D isk O perating S ystem)
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128K disk (implemented on EEPROM chip)
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27mW (approximately) transmitter using Si5351A synthesizer
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TCXO referenced frequency stability
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Band coverage 2200m to 2m
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LM75 temperature sensor
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Status LED
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USB interface for configuration, programming and easy firmware update (just copy the new
firmware file into the apparent USB Flash drive).
Simplest possible operation:
Just connect to U4B with a PC terminal emulator, and configure it with your callsign. Register the
flight name, details and channel on the QRP Labs website. Fly!
More flexible and advanced features:
U4B contains a wealth of flexibility and hardware expansion options which you can use to
customize your flight:
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19 GPIO pins – of which 9 can be configured as analog inputs and 8 are easily accessible
via PCB edge pads; all 19 can be used as digital input or output control pins
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I2C bus for connecting additional sensors e.g. pressure, humidity
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BASIC programming language with full-screen text editor, compiler and debugger
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128K Disk storage for your programs and data; BASIC can read/write data files
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Command line utility
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Telemetry over WSPR for relaying your additional sensor data
The U4B radio transmitter can transmit the following modes:
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QRP Labs tracking and telemetry over WSPR
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WSPR (including extended mode and slow 15-minute WSPR)
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JT9 (1, 2, 5, 10, 30 minutes)
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JT65 (modes A, B, C)
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Hellshreiber (standard, DX, and slow multi-tone FSK)
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CW (standard speed, QRSS, FSKCW and DFCW)
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Customized “Glyph” patterns can produce a unique idenfier on QRSS
U4B operating manual Rev 1.00
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