The Oxford 145.210 machine is located at the WMUB TV station site at the main Miami University Campus. The unit is inside the engineering room that is climate controlled and heavy loaded with a variety of electronic equipment. The unit is a Spectrum Communications SCR-1000B 10 watt repeater that utilizes an external power amplifier. The unit has performed well for over 15 years as it had come to us from the factory. In late 2005 we began having problems with intermodulation and poor receiver sensitivity mainly due to the heavy RF invironment the unit was now working in. Over 256 channels of Nextel, two 5 channel trunking systems, a multi access point broadband internet service, multi channel PCS cellular service, multiple satellite receivers, the head end unit of the campus' cable system, several VHF Police and Fire radio systems, and paging systems all add to the front end overloading of the "simple" amateur receiver.

2006 during a routine maintenance check, we discovered the unit would no longer accept touch tone commands that were needed to turn the transmitter on and off. Time for a major controller overhaul!

During the maintenance visit we found a few more changes had been made to the installation, without us knowing it! The duplexers had been located in another rack cabinate that was now gone to make room for back up batteries for the new 2.4 GHz internet access point. The duplexers were sitting on top of the batteries separated by a piece of cardboard to prevent them from shorting out the battery pack. Not good for either system.

The control circuitry covered 90% of the bottom of the chassis and even to the side walls of the repeater, not leaving any room for expansion.

The smaller (IC populated) board is the new CAT-200B repeater controller. It has been pre-wired for a RLS-1000 3 channel remote base control module that can be interfaced to mobile type radios for accessing other repeaters or ties into on site repeaters to link multiple bands together. The is now plenty of room for expansion!

Since the old controller utilized a lot of manually set functions such as time out timer, hand time, etc. via the front panel, those controls were no longer needed. The remaining knobs and buttons are power on/off, PTT and the metering! Everything else is set by touch tone control or computer programming for timers, voice messaging, CW ID (that's morse code for those licensed after 2007) etc.

A lot of rearranging equipment went on January 19, 2007. All of the equipment in the WMUB RACK 4 was removed and pushed skyward to make room for the duplexers in the bottom of the rack. The unit with the green display is a WMUB Satellite receiver. The Spectrum Communications 145.210 repeater is the next unit down from the top. The next panel under the Spectrum repeater is a remote receiver for the FARA 145.190 system. The panel under that holds a 35 amp power supply that powers the FARA remote receiver and the 145.210 power amplifier. The power amp. is the next rack mounted item. The duplexers are bolted to the rack for stability and are in the lower most portion of the rack. Blank cover plates were added to hide and protect the equipment. You can see most of the equipment mentions from the front (left photo) and rear (right photo).

The Ever Changing Face of 145.210

Finding a quality power amplifier to replace the failing Mirage amplifier became such a challenge that the repeater committee decided to put together a newer machine for the 145.210 site.

Many of the repeater sites are becoming saturated with RF. Appologies for the clarity of the photo as it was taken during a winter storm advisory! Easily seen is the density of antenna on this tower where 145.210 resides.

On top is a Motorola VHF repeater amplifier running about 80 watts. A pair of Mitrek mobile radios, the top one is the transmitter exciter (power amplifier has been removed and the exciter output is via a BNC connector on the right rear side.) The lower Mitrek is used for the receiver. We tried using the standard conversion of the Mitrek that would utilize one radio for both the transmitter and receiver, but were not satisfied with the desensing of the receiver when the transmitter was on the air.

In this photo you can see the exciter output, the CAT-200 control board, monitor speaker with on/off switch, red push to talk button for transmitter testing, PL board and power supply connections. The CAT-200 controller has been pre-wired for a CAT-RLS-1000 3 port remote base board. This will allow this machine to use up to 3 mobile transcievers to access other repeaters, or can be tied into other on site repeaters. Plans are to move this system to another nearby site where there are already a 220 and 440 repeater system to cross link into. The 3rd port would be used for the remote recieve site for the 145.210 system that will be located at the 145.330 repeater site. Likewise the new 145.210 site will have a 147.330 remote reciever as well.