RF Switch Selection Guide

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Consider the following parameters to select the

most suitable switch for a specific application:

1. RF Circuit - The three most common circuit configurations are (1) single-pole-double-throw (SPDT), (2) Transfer (DPDT), and (3) multiposition. Select the simplest circuit to meet system requirements.

2. Actuator - The Latching Actuator is recommended for first consideration because 1) current is required only during switching, and 2) minimal DC power is consumed. All latching switches are supplied with cut-off switches which de-energize the coil at the completion of the actuation cycle.

The Pulse Latching Actuator is similiar to the above. This type typically draws to little current that it can be left on continuously. Actuation requires a pulse length equal to or greater than the switching time. Elimination of the cut-off switches offers a higher reliability rating.

The Fail-Safe Actuator is used where system requirements dictate the switch return to the normally closed or fail-safe position when actuator power is removed. Most Charter Engineering fail-safe switches utilize magnetics rather than springs for fail-safe holding power.

The Momentary or normally open Actuator is used where system requirements require all output ports of the switch to be disconnected from the input port until a voltage is applied to a selected position.

3. Frequency - Specify the actual frequency to be used an minimum bandwidth. This often results in reduced testing time and associated costs. Generally, electromechanical switches are capable of higher-frequencies and greater bandwidths than necessary for the intended usage.

The following table correlates frequency and connector type:

Frequency Connector Note

26.5 GHz SMA Standard

21.0 GHz SMA Standard

18.0 GHz SMA Standard

16.5 GHz TNC Special Order

14.0 GHz N Special Order

12.4 GHz N Standard

12.4 GHz TNC Special Order

6.5 GHz SC Special Order

RF Connectors - Type SMA is the recommended connector expect for high power requirements. The normal frequency limit is 18.0 GHz; however, Charter Engineering can supply switches which function up to 26.5 GHz.

The Type N connector is recommended for optimum RF performance for operation at power levels greater than the SMA power rating. See CW Power Capability vs. Frequency Chart on page ?

The type TNC connector is recommended where power levels and frequency are high and the package is small. Sealed TNC connectors are also available.

The Type SC connector is recommended for high power applications in which large diameter cables are used for extremely low loss. SC is normally used up to 1000 MHz, but Charter Engineering has modified the design to operate up to 6.5 GHz and in special cases up to 10.0 GHz.

Type BNC connectors can also be supplied upon request.

4. Actuator Voltage - All standard Charter Engineering switches offer 28.0 Vdc. Other voltages can be supplied depending on the switch model. The following table consists of available voltage options for most CEI switches:

Please contact CEI for available voltage options for type TNC, BNC, and SC connectors.

5. Polarity - Each CEI switch offers the option of either a positive (+) or negative (-) common. The exception is the SPDT Failsafe series which does not require a common.

6. Power Interface - All standard Charter Engineering switches are provided with solder terminals. The MS connector (MIL-STANDARD) can be supplied instead of terminals on most switches. The MS connector is popular with higher power applications involving Type N connectors.

The D’ SUB Miniature series connectors may also used on most switches. Many catalog pictures feature D’SUB connectors which are readily available alternatives to solder terminals.

Charter Engineering can also supply other sources of power interface. Please contact CEI with your custom requirement.

7. Options -

Cut off Power Circuit - This applies to latching switches only. A switch that has the ability to disconnect the actuator drive circuit so that D.C. current will not be consumed after switching has been accomplished. Suppression Diodes must be specified with this option

TTL Logic - Transistor-transistor-logic driver circuitry enables the status of the switch to be controlled by the level of the TTL Logic input. Users can apply the power voltage across a pair of designated power terminals and then control switch operation with a 5 volt control circuit.

Custom - Charter Engineering can supply many types of electromechanical switches. Please contact CEI with your custom requirement.

8. Intermodulation - Passive Intermodulation (PIM) is a form of signal distortion that occurs whenever signals at two or more frequencies conduct simultaneously in a passive device (electromechanical switch) which contains some non-linear response. This interference phenomomenon is attributable to many sources such as dissimilar metals, dirty interconnects, or other anodic effects. PIM us of particular concern whenever:

Two or more transmitter channels share a common antenna

Transmitter signal levels are high

Receiver sensitivity is high

Transmitters and receivers share a common antenna

Two or more base station tranceivers are at a single site

Charter Engineering, Inc. recognizes the need for low PIM levels and offers specially designed electromechanical switches to meet low intermodulation requirements.

PIM measurements will vary depending upon carrier frequencies, power level, and PIM frequency. Charter Engineering, Inc. has certified the product line to meet the following criteria:

For further details, please contact Charter Engineering.