Actuator
The electromechanical mechanism which typically rotates 90° in order to achieve the different switch positions that transfers the RF paths from one position to another. The SMI actuator uses a rotary magnetic motor acting on a mechanical linkage to switch the RF paths.
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Bandwidth (Frequency Range)
The width of the pass band or operating band of a component.
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Baseball Switch
Refers to an electromechanical switch whose position indicator label resembles the stitching pattern
on a baseball.

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Coil
An assembly consisting of one or more windings of copper 'magnet' wire, usually wound on a form or bobbin when used in motors. It provides the actuating force to an electromechanical switch or relay's contact assembly.
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Contact Resistance
The electrical resistance across closed contacts as measured at their associated external terminals.
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Drive Head (DH)
The upper most portion of the switch. It contains the actuator, indicator circuitry and control connector.
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Dual Waveguide/Coaxial Switch
Dual Waveguide/Coaxial Switches combine waveguide and coaxial sections into one switch assembly. They utilize one actuator to drive the waveguide section and the coaxial section simultaneously.
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Electromechanical Switch
A mechanical switch (rotating waveguide rotor or moving coaxial contact bars) which is driven an by an actuator (magnetically operated sector motor).
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Failsafe
A switch that always returns the RF path to the de-energized position when there is no voltage applied to the actuator. Failsafe switches require continuously applied voltage to the actuator in order to maintain the RF path in the energized position; therefore MTBF is less than a latching switch.
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Ganged Coaxial Switch
Two or more coaxial switch sections which share one common actuator.  All sections are switched simultaneously.
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Hot Switching
RF power is applied to the switch during switch actuation. All SMI switching specifications are based on cold switching (RF power is not applied to the switch during switch actuation).
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Impedance
Impedance of an electronic device or transmission line is the ratio of the complex (vector) voltage between the conductors (or their equivalent) to the complex (vector) current on the conductors (or their equivalent). Impedance is the AC (vector) equivalent of DC resistance.
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Indicators or Tellbacks
A set of auxiliary DC contacts which are linked to the actuator and that switch with the RF paths. Indicators are normally used with pilot lights to indicate the position of the RF paths. They may also be used as interlocks or to provide status information to an external control system.
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Insertion Loss
The loss of energy attributed to any component (such as a switch, connector, filter, transmission line, etc.) which is inserted into a circuit. This loss is normally expressed in decibels (dB).
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Inhibit Contacts
Switch position indicator contacts which are adjusted to open or close only when the switch VSWR is less than 1.25:1.
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Isolation
RF energy may leak from one conductor to another by radiation, ionization, capacitive coupling, or inductive coupling. In the case of switching devices, isolation is the measurement of the power level at the unconnected RF output(s) as referred to the power traveling between the input and the connected output. Isolation is normally specified in dB below the Input power level.
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Latching
A switch with an actuator that will maintain a chosen RF path whether or not voltage is continuously applied to the actuator after switching is accomplished. 98% of all commercial switches are latching switches. After switching is accomplished, the coil drive line is automatically opened so that no current is present. This allows the voltage to be continuously present with no current drain.
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Locking Switch
Some applications require only authorized personnel to change switch positions. A lock option can be added whereby a key is required to operate the switch control.
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Negative Voltage Drive
Certain transistor circuits provide contact closure to ground as drives. In SMI’s standard circuits, positive voltage is applied to the common, B pin and pins A and C are returned to ground by the controller. The negative voltage drive option is required for this type of operation because drive polarity is reversed.
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Positive Voltage Drive
In SMI’s standard circuits, positive voltage is applied to pin A to achieve switch position 1 or pin C for switch position 2. Pin B is the power supply return.
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Power Handling
The capability of a microwave component or device to transmit a given amount of power through the device. In reference to an electromechanical switch, this is the ability to pass a given amount of RF or microwave energy after the contacts are closed. When electromechanical switches are used for power levels at or near their rated capacity, the RF or microwave energy should be removed during the switching cycle. Switching under power may be accomplished at significantly lower power levels, but it is difficult to establish a rating for such service because of the many external factors that affect this type of switching.
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Return Loss
The ratio expressed in dB, between the power incident upon a load or discontinuity and the power reflected from the load or discontinuity. It is equal to 20 times the log of the reciprocal of the reflection coefficient.
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Sealed Switch
A sealed switch can be mounted outdoors without any gross protection from atmospheric conditions. This option is specified by an “S” in the switch part number.
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Sheltered Switch
A sheltered switch is not suitable for unprotected outdoor use. This option is specified by an “W” in the switch part number.
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SPDT (Single Pole Double Throw)
A switch with one input and two outputs. Transfers the path from one output to the other output when the switch is actuated.
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Switching Time or Switching Speed
The total amount of time between application of the control voltage to the control or actuator terminals and the completion of contact closure, or switching.
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Transfer Switch
A switch with two inputs and two outputs. Transfers the RF path from one pair of output connectors to the other pair when the switch is actuated. Transfer switches are sometimes incorrectly referred to as DPDT (Double Pole Double Throw) switches.
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VSWR (Voltage Standing Wave Ratio or Vertical Standing Wave Ratio)
A measure of how efficiently RF power is transmitted from a power source, through transmission line, into a load. For example, RF power from an amplifier through a transmission line, to an antenna.
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