Overview
The MicroHunt is a specialized, ultra-compact continuous-wave (CW) beacon transmitter engineered by Bob Simmons (WB6EYV) under the Doppler DF Instruments brand. Primarily built for Amateur Radio Direction Finding (ARDF) competitions and high-altitude balloon telemetry tracking, the single-board module automates the transmission of Morse code identification patterns. The transmitter is designed with high-precision crystal timing components to facilitate multi-beacon sequential sharing on a singular radio frequency without data collisions.
Technical Specifications
| Attribute | Details |
| Manufacturer | Doppler DF Instruments / WB6EYV |
| Product Category | CW Transmitter Hunt Beacon (Fox Transmitter) |
| RF Power Output | 50 milliwatts nominal standard |
| Default Base Frequency | 146.565 MHz (National US T-Hunt Frequency) |
| Tuning Technology | Crystal-Controlled Phase-Locked Loop (PLL) Synthesizer Chipset |
| System Control Logic | Microchip PIC Microcontroller Hardware |
| Data Emission Mode | F2 (Tone-Modulated Continuous Wave over FM) |
| Target Code Speeds | Factory programmed at approximately 8 WPM or 15 WPM |
| High-Altitude Temperature Limit | Certified functional down to -70 degrees Celsius |
| Input Operating Voltage | 7 Volts to 12 Volts DC |
| Operational Current Load | 50 milliamperes (Transmit) / 5 milliamperes (Idle State) |
| Base Circuit Dimensions | 0.9 inches long by 1.2 inches wide |
Physical Description
The MicroHunt is constructed on an ultra-miniature, single-board substrate using high-density surface-mount technology (SMT) layouts. Due to its intended deployment as a hidden field node or an airborne payload component, the circuit lacks an integrated chassis, physical tuning knobs, or external alphanumeric displays. The bare module features dedicated contact points for DC power entry, an RF antenna output node, and explicit interface pins configured to directly couple with and drive external high-power radio frequency amplifiers.
History
The MicroHunt was engineered by Doppler DF Instruments to provide a stable, precision-timed target source for international-style radio orienteering contests, which are commonly called foxhunting. In standard multi-fox ARDF tournaments, up to five independent hidden transmitters share a single VHF frequency channel. To prevent mutual signal destruction, each station transmits its unique Morse identification token (such as the standard IARU MOE, MOI, or MOS sequences) for exactly 60 seconds before falling silent to let the next station broadcast. Traditional RC timing circuits were prone to thermal drift, causing separate transmitters to slowly overlap intervals and ruin a multi-hour competition.
Simmons resolved this synchronization vulnerability by utilizing a dedicated Microchip PIC microcomputer chip tied to a precise crystal oscillator core to manage the timing loop. This design held timing drift down to less than two seconds over six hours of continuous field deployment, allowing organizers to synchronize an entire array of beacons simultaneously by connecting their batteries in proper sequence at the staging area.
Beyond tracking sports, the module’s low weight and low idle current draw made it a reliable backup locator beacon for amateur rocket and free-flight weather balloon payloads. To adapt the 50-milliwatt footprint for long-range regional tracking operations, Doppler DF Instruments designed the board to pair with their optional MH+33 2-Watt class C power amplifier. This booster expansion allowed the MicroHunt to support alternate international A1 (on/off keyed carrier) or A2 (amplitude-modulated tone) emission standards over high-power 2-meter links.
References
- https://home.hiwaay.net/~pelican2/PicoDopp/MICROHUNT.htm – Product directory indexing factory board pricing, module dimensions, and baseline operating specifications for the transmitter.
- https://home.hiwaay.net/~pelican2/PicoDopp/MH_MORE.html – Engineering documentation detailing PLL synthesizer capabilities, high-altitude flight environmental benchmarks, and custom ordering configuration metrics.
- http://www.homingin.com/boxes.html – Technical equipment review log evaluating the timing synchronization capabilities, power profiles, and physical enclosure setups of the transmitter series during competitive field operations.