Electronic Engineering Dictionary

Header. The portion of a message that contains information used to guide the message to the correct destination. Normally a male connector having exposed pins which are molded into a plastic base. Headers are produced in either signal row or double row having a minimum of two pins. A 1-pin header would just a test-point. Common Headers are 0.1 inch spacing, pin-to-pin. Female connectors having the same spacing are used to interface. Headers are common in PC motherboards, and are very common as Jumper blocks. For more information and some graphics refer to Standard Headers. Also see Header Manufacturers

Head Room. Safety Margin. High-Temperature Operation

Heater. Same term as a Filament, see graphic to the right. A temperature stabilizer, sometimes shown as a serpentine trace when depicted within an IC package. A component used as a heater or temperature stabilizer could be nothing more than a resistor used to generate heat by allowing current to pass.

Heat Exchanger. An air-to-air or liquid-to-air finned duct arrangement which is used to transfer dissipated heat from a hot recirculating fluid to the cooling fluid by conduction through the finned surfaces.

Heat Shunt. A device (preferably a clip-on type) used to absorb heat and protect heat-sensitive components during soldering.

Heat Sink. A metallic device that dissipates or radiates into the surrounding air the heat that is generated from an integrated circuit or other device. [Heat Sink Manufacturers]. The point of the heat sink is to increase the surface area effected by the surrounding air. Most air cooled heat sinks are convection limited, and the overall thermal performance of an air cooled heat sink can often be improved significantly if more surface area can be exposed to the air stream. TO-3 Transistor Heatsink.

TO-3 Heat Sink

A component which is specifically designed to absorb, conduct or dissipate heat generated by an electrical and/or electronic component or an external source in order to prevent damage to the component.

Heat Sink Insulator. A component specifically designed to be thermally conductive and electrically insulating.

Heat Spreader. A metal heat exchanger or heat sink used with computer memory module DIMMs and other components to pull [spread] heat away from memory ICs or devices.

Helix. A spirally wound transmission line used in a traveling-wave tube to delay the forward progress of the input traveling wave. A large coil of wire. It acts as a coil and is used with variable inductors for impedance matching of high-power transmitters.

Helix House. A building at a transmitter site that contains antenna loading, coupling, and tuning circuits.

Henry (H). The electromagnetic unit of inductance or mutual inductance. The inductance of a circuit is 1 henry when a current variation of 1 ampere per second induces 1 volt. In electronics, smaller units are used, such as the millihenry (mH), which is one-thousandth of a henry (H), and the microhenry (uH) which is one-millionth of a henry.

Hermetic. Sealed so that an object is gas-tight to a specific rate, normally less than 1 x 10-6 cc/sec of helium.

Hermetic Seal. A hermetic seal results from fusing metal-to-metal, ceramic-to-metal, or glass-to-metal only. Hermetic sealing is the process by which an item is totally enclosed by a suitable metal structure or case by fusion of metallic or ceramic materials. This includes the fusion of metals by welding,brazing, or soldering; the fusion of ceramic materials under heat or pressure; and the fusion of ceramic material on to a metallic support. An air-tight seal.

Hertz (Hz). A unit of frequency equal to one cycle per second.

Heterodyne. To generate new frequencies by mixing two or more signals in a nonlinear device.

Heterodyne Detection. The use of an a.f. voltage to distinguish between available signals. The incoming cw signal is mixed with locally generated oscillations to give an a.f. output.

Heterodyning. The process of mixing two frequencies across a nonlinear impedance. The process of mixing the incoming signal with the local oscillator frequency. This produces the two fundamentals and the sum and difference frequencies.

Heterodyning Circuit. A circuit used to mix two frequencies together. A mixer. The example mixer shows two frequencies [G1 & G2] applied to a nonlinear impedance of diode D1. The primary of T1 along with the variable capacitor form the tuned circuit which selects the frequency. Read more about the types of Mixer Circuits.

Hexadecimal. Same as Sexadecimal. A number system with a base of sixteen; also pertains to conditions, choices, or selections that have sixteen possible values or states.

Hexadecimal System. Pertaining to the number system with a radix of sixteen. It uses the ten digits of the decimal system and the first six letters of the English alphabet. [Hex Table]