following parameters to select the most suitable switch for a specific
1. RF Circuit
- The three most common circuit configurations are (1)
single-pole-double-throw (SPDT), (2) Transfer (DPDT), and (3)
Select the simplest circuit to meet
2. Actuator - The Pulse
Latching Actuator is recommended. Actuation requires a pulse
length equal to or greater than the switching time. This type of
switch requires current only during switching and for a very short
period of time. A pulse width of 30 milleseconds minimum will more
than satisfy current requirements. There is also no need to supply DC
power to hold the selected position. Howerver, pulse latching can be
operated with continuous DC power supplied to the unit with no
degradation or decrease in life expectancy.
A latching switch with internally
cut off current circuitry can be obtained from CEI in some models
if your system is not equiped with pulse command circuitry. This
option will disconnect the drive circuit so that DC current will not
be consumed after switching has been accomplished.
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 utlize magnetics rather
than springs for fail-safe holding power.
The Mometary 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 as 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:
- Type SMA is the recommended connector expect for high power
requirements. The normal frequency limit is 26.5 GHz; however, Charter
Engineering can supply switches which function up to 40.0 GHz.
The Type N connector is recommended
for optimum RF performance and operation at
power levels greater than the SMA power rating.
See CW Power Capability vs. Frequency Chart.
The type TNC connector
is recommended where power levels and frequency are high and the
package is small.
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.
continued to page 2