My interest in assembling a remote base station for 6 meter FM started in the late 1970ís when I operated on 52.525 MHz simplex using a Motorola Motrac. This was a boat anchor but it worked very well. It had a good noise blanker, almost essential for 6 meter FM, and was capable of putting out an easy 100 Watts for it seemed hours at a time. This particular Motrac was mostly solid state except for two tubes, a driver and the final. Initially I planned to use this radio as part of the remote base set-up. There was no local 6 meter FM activity in the area at the time and the operating was limited to sporadic "E" opening during the spring and summer months and with limited openings near the end of December.
The remote base was essentially a UHF repeater tied to a 6 meter simplex radio. Using the 440 MHz band could help support local activity in this band because at the time (now the early 80ís) it did not have a great deal of activity either. The early 80ís did however bring some local 6 meter activity with a few other boat anchors being put on the air.
The remote base project was to be another low cost project. I acquired a UHF GE Exec II radio to be used as a repeater. The plan was to use this radio in conjunction with a Motorola Micor non-unified control shelf to be used for control, repeat functions, audio interfacing to the 6 meter radio etc. A Ferritronics PL (CTCSS) panel was also included along with a copy of a Motorola T1475 duplexer. Both the UHF repeater and the 6 meter radio were installed in separate Motorola Micor style base station cabinets. The 6 meter cabinet contained either a Motorola Mocom 70 or a Mitrek radio and a power supply. The Motrac could now be replaced with newer all solid state boat anchors as they became available. The cabinet also included a Micor repeater squelch gate used for audio interfacing and PTT control.
The plan was to have the remote base work as follows:
When a local station accessed UHF with a signal that did not include PL the signal would be repeated on UHF only. If the signal contained a 110.9 Hz PL tone the signal would be repeated on UHF and would also be repeated on 52.525 MHz. Any signal received on 52.525 MHz would automatically appear on UHF. UHF had priority. If there was a signal on 52.525 MHz and the local UHF users were only interested in talking on UHF using the repeat feature, no PL would be used and 6 meters would not be interfered with. Six meter audio would be heard on UHF during breaks in the UHF conversation. To indicate to the UHF user using PL that the 6 meter radio was being keyed by him or her, two squelch tails would be produces after the mic PTT button was released. The first one was generated by the UHF repeater receiver squelching and the second by the 6 meter radio going from transmit to receive before itís audio was squelched. To be more precise, the second squelch tail was a function of the external squelch control module (squelch gate) in the 6 meter cabinet. This module was also responsible for generating PTT for the UHF radio. The whole process was simple and worked very well. Many hams in the area were able to work many states while being mobile on UHF. There was no particular reason why a 110.9 Hz PL tone frequency was chosen other than the only UHF mobile radio I had at the time, a Motorola Mocom 70, had that PL frequency reed installed in it when the radio was taken out of commercial service. This may have been the earliest use of PL (CTCSS) in Amateur service in the Calgary area. Controlling the 6 meter radio using PL provided smoother (and probably more reliable) operation over DTMF.
The UHF repeater was equipped with a time out timer, Morse ID and modified tone control modules for on air control for both the 6 meter and UHF radios. Both transmitters could be controlled (disabled) from either 6 meters or UHF. A fan was installed on the repeater that blew air across the PA. It would only operate if the transmitter became active.
The remote base configuration was in operation for a number of years before the 6 meter radio was removed. The UHF repeater is still operational. As time went on, more ham radios became available equipped with 6 meters. Activity on 52.525 MHz was starting to fall off and people used other 6 meter frequencies. Since 52.525 MHz is the international calling frequency it became less acceptable to use this frequency other than for calling. A frequency change for the remote base was not considered.