" Duplex " might mean 3 things in this thread -
1. receive and transmit on different freqs (maybe "half duplex" to some people) (maybe also called "three way" by some people) (like taxi cabs)
2. repeater or non repeaterized ops
3. listen and talk at the same time ("full duplex" or "duplex duplex" as I like to call it)
Boston EMS seems to have the ability to use 462.95 in duplex, simplex, and half duplex modes. I am not sure if the BEMS dispatchers can receive and transmit at the same time on 462.95. I also dont know if the BEMS dispatchers can hear any field units that might be using 462.95 in direct/simplex mode.
Maybe the simplest way to sort this all out is to determine
- what freqs are the field units transmitting and receiving on ?
- what freqs are the dispatchers transmitting and receiving on ?
- are comms being "repeated" ?
- can anyone receive and transmit when someone else is receiving or transmitting ?
- can anyone receive and transmit at the same time ?
Peabody FD is the only nearby agency that I can think of where the dispatcher can hear the field units if they are on "direct" (they call it Channel 2)
Putting aside terminology:
1) A
transceiver can receive or transmit, but not both at the same time.
2) A typical
station (e.g., Quantar) has independent transmit and receive capability, and it can receive and transmit at the same time (so long as the Rx and Tx are on different frrequencies).
3) In a typical dispatch design, the dispatcher's speaker is wireline connected to the station's receiver and his mike is wireline connected to the station's transmitter (in both cases, through the comparator). The dispatcher can transmit and listen to subscribers at the same time. In addition, if the system is repeated (i.e., one transmitting subscriber can be heard by other subscribers), and if the comparator is so programmed, a subscriber can barge in over dispatch transmissions and be heard (at slightly reduced audo levels).
I believe that the accepted terminology is:
Simplex: all stations transmit and receive on the same frequency.
Duplex: dispatch transmits on F1 and listens on F2, while subscribers listen on F1 and transmit on F2. If such a system is not repeated, it is sometimes referred to as "two-frequency simplex." Some such systems are sometimes programmed to emit beeps on F1 while one subscriber is transmitting, to indicate that the F2 is in use and other subscribers should wait to transmit.
Repeater: a duplex station programmed such that activation of the station's receiver (non-voted) or the vote bus line (voted) activates the station's transmitter and passes received or voted audio to it, without any action on the part of the dispatcher required.
Half-duplex: a transceiver.
Full duplex: a station capable of receiving and transmitting at the same time.