which sat in a cradle with a direct dialing keyboard. These looked and functioned much like a landline, or hardwired, telephone. Unlike cellular handsets, these units passed through a dial tone when the receiver was lifted from the cradle and in this way seemed more like a landline telephone. There was a separate large radio transceiver chassis, typically measuring at least a foot square and 6 inches high, mounted either in the trunk or under the seats of an automobile. These transceivers were connected to the handset cradle with a multi-conductor cable usually around .5 inch thick. The mobile antennas almost always required a hole to be drilled in the body of the car to mount the antenna in; until the 1970s there were no "on-glass" antennas - these were developed later for the cellular car-mounted telephones. These whip antennas looked much like those used for CB radios and were about 19 in. long (1/4 wavelength at 155 MHz). These mobile telephone systems required a large amount of power (10 to 15 amperes at 12 volts) and this was supplied by thick power cabling connected directly to the automobile's battery. It therefore was quite possible and not uncommon for an IMTS telephone to drain an automobile's battery if used for moderate periods of time without the automobile engine running or if left on overnight. Optionally these units were also connected to the car's horn and could honk the horn as a ringer to summon a user who was away from the car. The IMTS units were full duplex, meaning that a user could both talk and hear the other party at the same time. This was an improvement over the earlier MTS systems, most of which were half duplex, allowing only one party to transmit at a time; the user had to "push to talk" to speak and then "unkey" the transmitter to hear the other party on the line. In 1960 General Electric introduced the "Progress Line" DTO- series MTS mobiles which were full duplex, although subscribers were still required to press the "push to talk" bar on the handset to speak. There were also IMTS handheld transceivers (Yaesu's 1982 vintage Traveler) that operated on 2-4 watts, and these were all half duplex. These were essentially modified "walkie-talkies" with a DTMF (dual tone multi-frequency) keypad attached on the front panel, which fooled the terminal into believing an IMTS mobile