G3TSO Mobile Antenna Page
Essential tips for tuning and optimizing mobile antennas in amateur radio.
Description
The G3TSO Mobile Antenna Page details construction and tuning methods for mobile antennas operating across 10 to 160 metres. The content describes a Hustler-based design, optimized for RF performance and vehicle speeds, featuring centre loading. For optimal operation on various bands, the loading coil placement requires clearance from the vehicle body.
Antenna resonance is critical for efficient mobile operation. A mobile antenna's base impedance may be as low as 27 ohms, requiring specific matching to achieve maximum radiation, as a minimum SWR at the transmitter does not always indicate resonance or maximum output. Tuning involves physical adjustment of antenna length to achieve resonance at the operating frequency. The G3TSO page outlines a tuning procedure utilizing a low-power signal source and a field strength meter to identify maximum radiation before impedance matching.
Loading coil placement, either at the base, center, or top of the antenna, influences radiation efficiency and mechanical stability for mobile installations. Centre-loaded whips, such as the Hustler design, offer a compromise between efficiency and stability, often for single-band operation. Helically wound antennas, including those for 28 MHz, may present base impedances around 17 ohms, resulting in a 3:1 SWR at resonance. Low resistance grounding at the antenna base is also specified for optimizing performance and minimizing RFI during mobile operation.
DXZone Focus: Mobile | Any | Antenna Tuning | HF