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Old 10-28-2008, 4:48 PM
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Default Console - Simplex Versus Duplex - Question

The local police dispatchers used to be able to transmit and receive at the same time using a UHF repeater system (471.1625R Mhz repeater output - 474.1625 Mhz input). I think they use a wireline connection to the repeater from the console - I dont hear the dispatchers on the 474 side. I think that someone told me that (all) dispatch consoles have a default setting to allow duplex comms (ie - the dispatcher can talk and listen at the same time). Apparently someone switched the console out of the default setting - now the dispatchers cannot listen when they are transmitting. It is not unusual to hear a field unit and a dispatcher both talking at the same time - and totally missing each others message.

Can anyone confirm that it would just take a flip of a switch to restore the "duplex" capability for the dispatchers. I need some really firm info - I want to present this to the police and fire chiefs. (Fire channel has the same deal on 460.60R).

$500K was spent to renovate the 911 center last year - I presume that they have 2 brand new consoles.

Maybe this has something to do with a lack of (??) '4 wire' phone lines from the telephone company. However, my town has 2 cable providers, FIOS, municpal fire alarm cable system, and I think a municipal fiber optic loop - maybe some Town microwave as well. I cannot imagine that there could be any real problem in getting the audio from the 911 Center to the repeater site. In fact, the repeater site might be right at the 911 Center (with a backup repeater on a hilltop).

Thanks - Peter Sz

PS - I am not looking for a debate on the meaning of "duplex" - I am not looking for the pros and cons of running duplex. I did a quick check of the archives - I didnt see this topic discussed recently.
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Old 10-28-2008, 5:40 PM
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Without knowing the specifics of the console that was installed (I take it this is Arlington PD), your question cannot be answered as posed.

However, as a general matter, consoles that work 4-wire wireline channels can be programmed for either full duplex or simplex operation, where here the terms mean:

Duplex: the receiver audio on the input frequency remains on the "select" speaker even while the console operator is transmitting, albeit at a diminished level; and

Simplex: the receiver audio on the input frequency is muted while the console operator is transmitting.

With the consoles that I am most familiar with, this is as simple as setting Switch 8 ("FD") on the dual channel card to "on."
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Old 10-28-2008, 5:41 PM
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Depending on the make/model of the new consoles, you're most likely correct, they CAN be put in half-duplex mode. The field radios cannot receive when they are transmitting (with a few exotic exceptions) but the consoles should be able to receive units in the field while they are transmitting.

HOWEVER, if the equipment between the field radio and console isn't set up for it (or can't support it) all bets are off again even if the console is set up.

Bottom line, can't hurt to ask!
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