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Hot switching and cold switching are terms used in the context of RF/microwave switches to describe the conditions under which the switches are operated. These conditions are related to the presence or absence of RF/microwave power at the ports of the switch during the switching process and have implications for the switch’s performance and longevity.
Hot Switching
Hot switching occurs when RF/microwave power is present at the ports of the switch at the time of the switching action. In other words, the switch is changed from one position to another while it is actively carrying RF signals. This can cause stress on the internal contacts of the switch, potentially leading to premature failure. When the circuit carrying power is opened or closed, there may be arcing between the contacts, similar to an electrical arc. This arcing can degrade the switch contacts by leaving deposits and causing burns on the contact surfaces.
Note FIG 2 below.
Cold Switching
Cold switching occurs when the RF/microwave power is removed before the switching action takes place. In this scenario, the switch is changed from one position to another without any RF power present at its ports. Cold switching results in lower stress on the internal contacts, leading to longer switch life compared to hot switching. All CEI switches should be operated when power is removed (cold switching) prior to the switching process. Otherwise and depending on the power level of hot switching, the switch may no longer offer the expected RF performance.
Note FIG 1 below.
Additional Factors
Power Handling
The power handling rating for cold switching is typically referred to by end users when selecting switches for their applications. It indicates the maximum power level the switch can safely handle during switching when there is no RF/microwave power present at its ports. All CEI switches using SMA, Type N, and Type SC connectors offer a higher power level option by adding the suffix “/P” for increased power capacity. This power chart can be found here for reference.
Operating Temperature
It is also important to consider the operating temperature of the switch when assessing its power handling capabilities. The power handling specifications are often provided at a specific operating temperature we define as 25 °C (ambient room temperature) to reflect the realistic conditions under which the switch will be used. Higher ambient temperatures, altitude, and VSWR can reduce the maximum power handling capability of the switch. Please reference the power handling chart from the link above.
In summary, hot switching involves switching a switch while it is actively carrying RF/microwave power, which can stress the internal contacts and cause premature failure. Cold switching is performed with no RF/microwave power at the ports, resulting in lower contact stress and longer switch life. Please use all CEI switches while cold switching only or contact CEI for additional information.