ICR is a very important feature for voted repeaters, and is (as far as I can tell) unique to Motorola.

A voted repeater will work without a squelch gate. It is essentially a dedicated transmitter and receiver without the ability to repeat on its own. If, however, something happens to the voting comparator, the station cannot repeat. The addition of an ICR squelch gate provides recovery from the loss of the comparator. It works like this:

If a signal hits a normal squelch gate, it keys the transmitter and enables the receiver to transmitter (repeat) audio path nearly instaneously. A normal squelch gate would override the operation of the voting system since it would control repeater operation.

In a voting system, it takes a couple hundred milliseconds for a satellite receiver (including the one in the station) to decode PL and drop idle tone; then it takes the comparator a few ms. to notice the loss of idle tone and to make a receiver decision, then generate the tone keying sequence to key the repeater transmitter.

An ICR squelch gate has a value change of one capacitor--the one that determines how quickly the SG keys the repeater. The ICR SG will not key the transmitter for about 300-400ms after it sees a signal. This gives the comparator time to make a receiver choice, generate keying tones, and gives the station time to key up.

If the station does not "see" keying tones within that 300-400ms window, it assumes that the comparator has failed and goes ahead and keys the station as a normal repeater. When the comparator comes back on line, it will key the transmitter within the window and the ICR SG will stay dormant.

This can be very handy.

One caveat: if you use RF linked satellite receivers, you have to take into account the added key-up/decode delay of the RF link(s) vs. the lack of delay in the station receiver. You may have to increase the size of the delay cap to accomodate this additional delay.

Rant:

This simple little function is one of the many things which separate high-spec Motorola repeaters from the pretenders, along with a few other little things. ICR has been an available function since MICOR, and probably before that to the beginning of voting systems. It is currently an inherent function (software enabled) in current high-end repeaters from Motorola such as Quantar, and it can be approximated in MTR2000 by running the MTR in repeater mode (instead of base station mode) and making the tone remote interface the priority keying means in software. The MTR will key up in repeater mode then remote control will take over when keying tones come in.

It is system-oriented, fault-tolerant, in-depth thinking like this that makes Motorola worth the money, and all the rest of them so much ........well, whatever........when the hair gets short, the chips are down, and the system has got to work.

End of Rant. :-)