These Techoman 49:1 baluns / ununs are designed to efficiently match the high impedance (~2450 ohms) of an end-fed half-wave (EFHW) antenna to the 50-ohm impedance of standard 50 ohm coaxial feedlines and HF transceivers.
Features and Specifications:
- Frequency Bandwidth: 1.8 to 30 MHz
- Efficient power transfer between the radio and the antenna,
- Improved radiation efficiency on multiple amateur radio bands,
- Typically allows the EFHW antenna to operate on harmonically related bands (e.g., 10m, 20m, 40m, 80m) with minimal need for an antenna tuner or in some cases no tuner.
- Maximum transmit power: 100 watts PEP (SSB); 20 watts Data ICAS.
- Earth stake from SO239 or PL259 connection suggested to reduce stray RF currents on coaxial cable (may not be necessary for QRP operation).
The 49:1 balun / unun steps down the impedance as follows:
- EFHW antenna at resonance: ~2450 ohms (on its resonant frequency),
- 49:1 transformation ratio: √49 = 7:1 voltage ratio → 7² = 49:1 impedance ratio,
- Resulting in: 2450 ohms ÷ 49 ≈ 50 ohms, which matches the coax and transceiver.