I'm trying to design circuit for controlling this rf switch (87104C, T24 Option)


as i'm understand it say

to Select (close) desired RF path by applying TTL “High” to the corresponding “drive” pin

and also if i want

To select another path, ensure that all unwanted RF path “drive” pins are at TTL “Low” (to prevent multiple RF path engagement). Apply TTL “High” to the “drive” pin which corresponds to the desired RF path

which means if i wish to control the switch all i had to do is driving or undriving the "Drive" pins but here is a question in this RF switch there is "Position Indicators", i researched and get this

The indicator (IND) is a set of DC Switch Circuitry that is designed to switch in parallel with the RF switching.

and the Datasheet of this Switch says

These switches have an interrupt circuit that provides logic to open all but the selected ports, and then closes the selected paths. All other paths are terminated with 50 Ω loads, and the current to all the solenoids is then cut off. These versions also offer independent indicators that are controlled by optical interrupts in the switch. The indicators provide a closed path between the indicator common pin and the corresponding sense pin of the selected path

what is the use of those "ind" pins when i can just controlling switch by using "drive" pins


1 Answer 1


"The electronic position indicators consist of optically isolated, solid state relays which are driven by photoelectric sensors coupled to the mechanical position of the RF path’s moving elements."

These are not drive or *inputs, they are outputs to show that the actual position of the mechanical relay.

Simply telling a relay to switch, and taking on faith that it has successfully switched to the desired state, might not be acceptable in mission-critical uses. For example, it would be important for a user to know that he is actually transmitting an urgent message, rather than talking to a "dead mike". It would useful to have an indicator that confirms the transmit relay is in the correct position.

  • \$\begingroup\$ thank you sir :) \$\endgroup\$
    – Settasak
    Jun 17, 2023 at 17:55

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