![]() Once calibrated, returning the motor to a particular position should yield the desired resonant frequency. Such systems calibrate the loop by recording the motor position for various desired frequencies. Many systems use stepper motors which generally provide a high degree of positional accuracy and repeatability. ![]() ![]() In my experience, the tuning systems available generally rely on open loop motor position in order to tune the antenna. I can't claim to have looked at all of them but I have considered a few. There are many homebrew magnetic loop tuning systems out there on the net. Therefore the tuning is an electromechanical system subject to error and change over time. The variable capacitor is generally driven by a motor. The variable capacitor is used to tune the loop in order to achieve resonance. Generally the variable capacitor can either be tuned by hand or in the case of my project from a geared down motor drive system.Īs was previously mentioned, the magnetic loop consists of an inductive loop connected to a variable capacitor. The challenge is to tune the magnetic loop reliably and quickly - the purpose of this project is to provide the magnetic loop operator/enthusiast with an electronic system to achieve this.Īs has been mentioned, the magnetic loop needs to be tuned and the tuning device is a variable capacitor. The VSWR increases rapidly when the loop is no longer resonant. If the loop is well constructed and at the resonant frequency, the measured VSWR maybe close to 1:1. At the desired operating frequency, the system is resonant with an operating bandwidth of only a few tens of kilohertz. The main loop forms an inductor and to tune the loop, a variable capacitor is connected across the inductive loop. The main loop is not physically connected to the coupling system of choice. RF energy is coupled to the main loop in a variety of possible ways such as a small coupling loop, transformer coupling or a gamma coupler to name but a few. The magnetic loop is a resonant tuned loop. So if you want a performance antenna to operate mobile or in a small space, the magnetic loop is a very worth while candidate. A magnetic loop antenna also has the advantage of performing well when close to or at ground level compared to a traditonal antenna which generally performs poorly unless mounted at a suitable band dependant height. This has the advantage that very few harmonics are radiated while transmitting and when receiving the narrow band, nature acts as a preselector preventing overdrive of the receiver and provides narrow band noise performance. ![]() Magnetic loop antennas have the advantage of being relatively compact and are quite narrow-banded. They are termed "magnetic" because they pick up the magnetic component of an electromagnetic field, unlike the traditional antenna designs such as dipoles, yagi and verticals which only respond to the electrical component. I expect you already know the advantages/disadvantages and the challenges of such an antenna design. ![]() I am assuming if you have found this instructable and have taken enough interest to read it, you probably already know what a magnetic loop antenna is. I do not intend to go into huge depth regarding magnetic loop antenna design as this article is centered on my automated tuning system and I am making the assumption the reader is already somewhat familiar with magnetic loop antenna construction and operation. Before we get deep into the project, I intend to outline what a magnetic loop antenna is and why this project came about. I am very pleased to publish details of my latest project which is a magnetic loop (ML) antenna automated tuner. Hello community - Dave here (radio callsign G7IYK), ![]()
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