Definition
An electrical circuit consisting of an inductor (coil) and a capacitor connected together, which stores and exchanges electrical energy back and forth between the two components. At a specific frequency, called the resonant frequency, the circuit oscillates strongly, making it useful for tuning radio transmitters and receivers to a chosen frequency.
Plain English
A small circuit made of a coil and a capacitor that naturally bounces electrical energy back and forth at one specific frequency. By choosing the right coil and capacitor, you can tune it to whatever frequency you want, which is how radios pick out one station from all the others in the air.
Context Anchor
Seen in avionics, radio, navigation receiver, and aircraft electrical system discussions.
Derivation
Called a 'tank' because it stores electrical energy the same way a water tank stores water. Energy sloshes back and forth between the coil (which holds energy in a magnetic field) and the capacitor (which holds energy in an electric field), much like water sloshing between two connected containers.
Why Pilots Care
A properly functioning tank circuit produces clear radio reception and accurate navigation signals; a faulty one causes weak or noisy comms and unreliable navaid reception.
Analogy
Like a child on a swing: push at the right rhythm and the swing builds up motion easily. A tank circuit has its own natural rhythm (its resonant frequency), and signals at that rhythm pass through strongly while others fade away.
Intuition Check
“Tank” does not mean a fuel tank here. It means an electrical circuit that briefly stores and trades energy inside radio equipment.
Example Sentence 1
The tank circuit in the COM radio is what lets the pilot tune in 122.8 without picking up nearby frequencies.
Example Sentence 2
During preflight checks the ADF receiver relied on its tank circuit to lock onto the correct beacon signal.