There were two basic repeat modes used in the Medical Telemetry systems. The Med 1 through 8 and the two dispatch channels (now known as Med 9 and 10) are duplex channels. The Orange Box and the Apcor (both Motorola) and some others were duplex hand carried units. I will focus first on the Orange Box and The Apcor.
Both units were duplex and transmitted to the base on the traditional mobile higher frequency. The orange Box had a repeat function that would retransmit the base TX freq through the mobile freq. The base station ran in duplex mode, not repeated. This way, a portable radio (like a COR HT220 model) would transmoit through the Orange Box to the base and the base would transmit through the Orange Box to the portable. The portable was also configured like a base station channel-wise. It worked! The 12W APCOR worked the same way. The EMD mobile repeater was a duplex Micor 10 channel radio with a separate Pac_rt radio receiver. The mobile would transmit on the mobile freq and would receive on both the Base channel and a 458MHz channel (there are 4 of them) simultaniously and repeate the audio back out through the mobile freq. The base would operate in non-repeated mode. The would allow a full-duplex conversation, although it isn't technically full duplex - it just works that way. The porable unit talking to the Mobile was a 1 watt APCOR radio that talked on the 458 channel and listened on the 468 channel, thereby giving the entire conversation duplex functionality. So - that's how all this worked. The Mobile and APCOR portable combined cost almost $5K in the mid-late 70s. That was more than a car cost! Motorola has lots of bells and whistles on it. The mobile was SP all the way and the APCOR was a costly device. Doug in Seattle now, Florida then
