Toroidal Antenna Tuning Circuit for Rapid Multi-Band Switching
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Solution Overview
Problem
Existing mobile HF antennas are inefficient due to high stray capacitance, large and expensive automatic screwdriver antennas, and instability in impedance matching, particularly when switching between frequency bands, which affects power transfer and usability.
Innovation Solution
An automatically tunable mobile antenna system using series-connected toroidal coils with binary inductance values and a shunt coil, controlled by a remote controller and relays to minimize stray capacitance and achieve impedance matching, allowing for rapid frequency switching without the need for manual adjustments or expensive components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a motor-driven shorting circuit is used to change frequency bands, then impedance matching can be achieved across multiple bands, but the switching time becomes excessively long (up to 3 minutes)
Solution Approach 1:
The loading coil is divided into multiple discrete sections with binary-weighted inductance values (1, 2, 4, 8, 16, 32, 64 microhenries). Each section can be independently switched in or out of the circuit using relays, allowing rapid reconfiguration of total inductance to match different frequency bands without mechanical movement.
Solution Approach 2:
The motor-driven mechanical shorting circuit is replaced with an electronic relay-based switching system. Relays provide instantaneous electrical switching of coil sections, eliminating the 3-minute mechanical adjustment time while achieving the same impedance matching function across multiple bands.
2Adaptability or versatility
If antenna tuners are used at the base of the whip for impedance matching, then frequency adaptation is improved, but stray capacitance increases and power transfer efficiency decreases
Solution Approach 1:
The impedance matching function is extracted from a separate antenna tuner device and integrated directly into the loading coil assembly at the base of the whip. By placing the switching circuitry and coil sections directly at the antenna base, the patent eliminates the need for external tuner components that would introduce additional stray capacitance and reduce power transfer efficiency.
3Reliability
If large coils are used to achieve high Q factor, then antenna performance is improved, but the antenna size and cost increase significantly
Solution Approach 1:
The loading coil is segmented into multiple smaller coil sections with binary-weighted inductance values. This segmentation allows the antenna to achieve high Q factor through optimized inductance selection for each frequency band without requiring a single large coil, thereby reducing overall antenna size and material cost.
Solution Approach 2:
The patent changes the inductance parameter dynamically by switching between different coil sections based on the operating frequency band. This allows the antenna to maintain optimal Q factor across multiple bands using smaller, more compact coil sections rather than requiring one large coil for all frequencies.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides efficient impedance matching, reduces size and cost, and minimizes crosstalk, enabling quick and stable frequency switching while maintaining high Q factor performance, making it suitable for general-purpose amateur radios.
Implementation Method 1
a toroidal inductor including a plurality of windings of electrically conductive wire... selectively electrically short at least one of the windings of wire contacted by the movable contact arm, thereby changing an inductance of the toroidal inductor
Implementation Method 2
by rotating the shaft within the center region of the toroidal inductor, the movable contact arm rotates so as to selectively electrically short at least one of the windings of wire contacted by the movable contact arm
Data Source
AI summary
In accordance with some embodiments, an automatically tunable mobile antenna is provided with toroidal inductors connected in series between the antenna feed point and a whip and a shunt inductor to ground at the RF input, with the inductors forming an L network impedance matching circuit having values which are in a binary sequence and which are selectively added to impedance match the whip to the output impedance of a transmitter. In accordance with some embodiments, an automatically tunable mobile antenna is provided with a variable toroidal inductor assembly connected between the antenna feed point and the whip having a variable inductance based on selective shorting and un-shorting of wire windings to impedance match the whip to the output impedance of the transmitter.