N6OCS
The Nucleus Transmitter
A "stock" C-net Nucleus Paging station
The N6OCS repeater is based on a Motorola Nucleus II 900 MHz paging station with c-net control for the transmitter, power amplifier, power supplies and mounting chassis. While there are less expensive ways to build a 900 repeater, the Nucleus seems like a great choice. The Nucleus II is a 300 watt station designed to run 24/7 at full power, so with it turned down to 100 watts it should cruise along with a high degree of reliability. Since it was designed to operate in the harsh environment of a commercial site with a lot of RF noise it should be immune to some of the intermod problems that can plague lesser radios. The Nucleus also has a very stable oscillator and time base section that can be disciplined from an external source ie. GPS receiver. Although the Nucleus is a bit power hungry it seems to be a clear cut choice over a modified mobile radio.
Modifications to the Nucleus is fairly simple and non-intrusive.
The Nucleus used in this project is the C-net version which requires a few modifications. The Nucleus modifications are fairly straight forward and require three connections to the back plane and one trace cut on the exciter board. My goal was to keep the Nuc as unmolested as possible so it would remain modularized for service.
I soldered a lead (grey wire) to the shield then covered it with heat shrink and soldered the other end to pins 57 & 61 of J7 for the ground. I used 2 ground pins here for strain relief. It appears that all of the ground pins on these connections have square solder pads and all others are round.
The orange lead is soldered to pin 24 on J8. This is the external key line. You can also find it on pin 10 of J17, the 50-pin telco connector. This line needs to be pulled low to key up the transmitter. However it can be selected as a pull high from the command menu. I set mine for low. The Nuc draws about 180 ma to pull down this line so I installed a simple relay to take the load off the controller.
The blue wire is the audio input to the exciter and is soldered to pin 60 of J7. You can also pick this off at Pin 78 on J9 . I choose J7 because it was closest to the J8 connector and I didn’t want to have wires running all over the place. This is straight forward except the SCM board puts a heavy, low impedance load on this line. The best solution that I came up with was to cut the trace on the exciter board from pin 60. This is easily repairable and easily repeatable on spare exciters.
The Nucleus interface connector is a 3 pin, female “DTC” connector. Pin 1 = ground (black), pin 2 = audio (blue),pin 3 = PTT (orange). The controller end is male.
The image on the left is the double circulator or isolator. The photo on the right is the isolator, load and low pass filter assembly
I’ll fill in the blanks soon.. .. .. Promise
more to come!