This class includes:
(1) Tuners (as defined in the Glossary). In function the tuner serves to select and pass or reject a particular frequency from a signal presented to the tuned circuit while attenuating or suppressing the passage or rejection of any other frequency that may be present in the signal. Generally the tuner consists of an inductor and capacitor, one or both of which may be variable, connected together in such a manner as to form a resonant circuit. For classification here, some means must be present in the tuner to vary the mean resonant frequency of the tuner from one frequency to another. The means present in the tuner should be something more than just the incidental showing of a generalized variable impedance element, but should be some means which is included in the circuit for the express purpose of making the resonant circuit variable over a range of frequencies. This means usually is in the form of a specific variable impedance device, such as an inductor or capacitor, the variation of which changes the electrical parameters of the circuit thus causing a shift in resonance of the circuit. The means may, however, consist of two or more impedances of fixed value which are adapted to be switched or substituted into or out of the resonant circuit. Excluded are wave filters which are closely analogous in that they are designed to pass or reject a single frequency or band of frequencies. Wave filters, generally, have no provisions or means which are particularly designed for and meant to vary the mean frequency of the filter during operation of the filter unit in a radio circuit. The wave filter may have "trimmer" means which is designed to "peak" the response of the filter, but these trimmers are not meant to be used in varying the resonance frequency of the filter during the operation of the filter in an electrical circuit such as, for example, a radio receiver. A wave filter having trimmer means is usually adjusted prior to the installing of the filter in an electrical circuit. The filter once adjusted is rarely, if ever, adjusted again unless the resonance characteristic of the filter requires some additional peaking. A circuit which has means to merely broaden or narrow the band which is being passed without varying or changing the means or center frequency to which the circuit is tuned does not amount to tuning but is considered a filter for classificaiton with wave transmission lines and networks (see References to Other Classes, below). However, a circuit which broadens or narrows the pass band and which also varies the mean or center frequency of a filter is considered a tuner.
(2) Included also are tuners with perfecting structure, such as a remote control circuit, a resonance indicator, tuner units with an electromagnetic operator, or tuners with automatic frequency centering circuits which are not otherwise classifiable.
(3) Also included are tuners combined with or incorporated in other structure and not elsewhere classifiable, such as a tuner combined with a tube socket or a special punched chassis. Also included are tuners combined with or incorporated in diverse nonelectrical devices and which combination is not classifiable elsewhere.
(4) Included also are tuners constructed as by the type of actuator used or from selected material so that the impedance values of the tuner changes particularly well in response to a particular condition or change in a particular condition such as current and/or voltage as, for example; a tuner using a saturable core type inductor; a tuner using a voltage responsive capacitor; or a tuner responsive to a magnetic field. Also included are tuners usually of the mechanically variable type together with a condition sensing actuator which changes the mechanical adjustment of the tuner in response to a condition or a change in condition. An example, of such a tuner is one having a heat sensitive actuator, or a tuner that is deformable as by compression by a weight or force.
(5) Subcombinations and components of tuners not otherwise classifiable, such as a resonance indicator, are classified in this class.
Lines with other classes and within this class
A. TUNERS CLASSIFIED ELSEWHERE:
Certain circuits or devices which may be considered tuners are not classified here. See References to Other Classes, below, for tuned resonance type wave filters which may be referred to as a tuner and the resistor-capacitor circuits such as bridged-T, double-T or Weir Bridge networks, for example, which are sometimes referred to as tuners. Also see the Search Class notes for tunable resonators of the distributed parameter type in which there are no lumped impedance elements present and where only a single resonator is used. The inclusion of a lumped impedance element in the resonant circuit or the coupling of two or more distributed parameter type units together to form a single tuner will result in classification in this class.
B. TUNERS COMBINED WITH OR INCORPORATED IN OTHER DEVICES:
As stated above, this class includes tuners combined with or incorporated in other structure not elsewhere classified. See Subclass References to the Current Class for tuners combined with various other devices and for tuners combined with or having shielding or housing means. The combination of a tuner with or in other structure or circuits is very common. A partial list of the classes and subclasses including this combination is given in References to Other Classes, below.
C. TUNER COMPONENTS AND SUBCOMBINATIONS:
Included in References to Other Classes, below, is the classification of the most common subject matter which may constitute a part or subcombination of a tuner.
D. DEVICES SIMULATING TUNERS:
See References to Other Classes, below, for wave filters, and resonators of the distributed parameter type.
E. MEASURING OR TESTING TUNERS
This class does not provide for either methods of or apparatus for measuring and testing tuners. If the measuring or testing is of a mechanical nature or not otherwise classified, classification is in Class 73, Measuring and Testing. See also the Search Notes in Class 73 for a more detailed field of search to measuring and testing devices and systems. If the measuring or testing involves determining the frequency or electrical properties of the tuner, classification is in Class 324, Electricity: Measuring and Testing, subclasses 600+.