page_title: Trimmer (electronics)
section_title: Tuned circuits
hierarchical_section_title: Trimmer (electronics) / Tuned circuits
caption_attribution_description: English: Drawing of an IF (intermediate frequency) transformer with the front surface of the shield can cut away to show the transformer itself. An IF transformer is a resonant transformer used as a bandpass filter in the intermediate frequency section of a superheterodyne receiver. It consists of two windings of fine wire (flat cylinders) around a tube containing an adjustable powdered iron slug core. Each winding has an adjustable mica capacitor (top) connected across it to make a resonant circuit. The two resonant circuits are adjusted so their resonant frequencies are equal to the intermediate frequency of the receiver. The resonant transformer has a much higher Q factor than an ordinary resonant circuit, and is responsible for the selectivity of the receiver, allowing through a narrow band of frequencies from the desired radio station and rejecting nearby stations. Several IF transformers are used in the typical superheterodyne. The aluminum can surrounding it shields nearby stages from its electromagnetic field, preventing feedback which can cause parasitic oscillations
context_page_description: A trimmer is a miniature adjustable electrical component. It is meant to be set correctly when installed in some device, and never seen or adjusted by the device's user. Trimmers can be variable resistors, variable capacitors, or trimmable inductors. They are common in precision circuitry like A/V components, and may need to be adjusted when the equipment is serviced. Trimpots are often used to initially calibrate equipment after manufacturing. Unlike many other variable controls, trimmers are mounted directly on circuit boards, turned with a small screwdriver and rated for many fewer adjustments over their lifetime. Trimmers like trimmable inductors and trimmable capacitors are usually found in superhet radio and television receivers, in the intermediate frequency, oscillator and radio frequency circuits. They are adjusted into the right position during the alignment procedure of the receiver.
  Presets in electronics are adjustable components to which the user of the device has no access. They are intended to be set during manufacture or as part of maintenance and repair. A range of different passive components can be made as presets, including resistors, capacitors, and inductors.
context_section_description: An adjustable tuned circuit can be formed in the same way as a preset inductor.  The inductor and its resonant capacitor are commonly contained in a metal can for shielding with a hole at the top to give access to the adjustable core.  Tuned transformers can also be constructed this way with two windings on the same core.  This is a common component in the IF stage of radios which have a double-tuned amplifier format.
caption: IF transformer cutaway
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