PURC5000 Station Background Information

The following thread was recently posted on the repeater-builder Yahoo! Group and was slightly edited for publication here. Repeater-builder thanks the contributors for permission to present their comments.

The PURC5000 came in two versions:

  • Early CxxJLB stations, similar to early MSFs, where the 2732 eprom is programmed via the R1801 suitcase programmer for frequency, etc.

  • Later CxxJXB stations, while similar to later MSFs, DID NOT need RSS. There is a 10 or 12 button keypad, and a red LED scrolling display (similar to the later NUC stations), which can be used to set a number of station parameters, such as frequency, key tones, etc. HOWEVER, in order to be able to change the frequencies, there is a DIP switch on the control board that needs to be turned on to allow the changes to take effect. Otherwise, the display will show the current frequencies programmed for CH1, CH2, etc, but not accept changes.

    Most of the PURC5000s came with a "link receiver" drawer just below the HSO. This is simply a tray with a MICOR RF/IF board, a MICOR style audio/squelch board (usually modified for flat audio by using a different resistor value in the preamp op-amp stage before the PL filter in/out), and usually a DPL board. Plus there is a vertical interconnect board to tie it all together, supply regulated 9.6v and 12v from a single 12v feed, and provide all signals out to a 10-pin header connector. This header connector then ties to the MSF5000 control board via a 10-conductor ribbon cable.

    I've taken these receiver trays out of old PURC5000s, swapped the 70 MHz RF/IF board with a 450 MHz mobile RF/IF board, swapped the DPL board for a PL board, and wired an 8-conductor shielded cable from the interconnect board out to a DB9 connector, and ran a fused DC power cable into it. Makes an excellent voting site receiver, or a great repeater receiver if using a repeater other than a MICOR Compa-station.

    I can still remember years ago when my Motorola rep would make his monthly lunch visit. One day he excitedly called me to tell me he was bringing me a new protoype paging transmitter - 300 watts, and he could carry it in the trunk of his sedan with only one person needed to lift it in and out. Thinking of the 300w PURC5000s, which weren't in the shallow compa-station cabinets like MSFs, but rather in 6ft tall 24" square cabinets, requiring an army to move, we thought he was crazy, until we actually saw it in his trunk. Shortly thereafter, 60 PURC5000s went to the boneyard, and over 300 Nucleus stations soon followed.

    Some Motorola trivia - while the PURC5000 was a retrofitted MSF5000, the Quantar actually was derived from the Nucleus station, which came first.

    Speaking of Nucleus stations - anyone wanting to make a 900 Nucleus into a repeater - keep your eyes out for what was known as an "ADVANCED CONTROL" Nucleus - basically, instead of an NIU (Network Interface Unit which is fed via a satellite synchronous RS232 data stream link), the station came with an Advanced Control board, which allowed either a standard RF link receiver or wireline control. Early versions included a PURC500 style receiver tray bolted below the power amplifier (same receiver as the PURC5000s mentioned above), while later versions utilized the internal card receiver (like a Quantar).

    The link control card is matched to the Station Control Module (SCM), so when switching out the link control card, the SCM also needs to be replaced. Later version software also required the exciter to be replaced whenever the SCM is changed, as they are known as a "matched pair" which is factory aligned.

    The advantage of the "Advanced Control" version is that the exciter can be modulated in the analog domain - perfect for amateur use. Unfortunately, this version is extremely rare, and only a handful were sold. It was designed as a replacement for the later PURC5000. The main market was those who had RF or wireline linked PURC5000 simulcast systems, and needed new units for coverage expansion during the period after the PURC5000 was discontinued. But by that time, most of the larger paging carriers went to satellite-based linking of their simulcast networks, and mass converted to NIU-based NUCs, thus the reason they are so rare.