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West Michigan Obscene Technology, Now with D-Star WD8EMD




Dan, N8WKM with his 900MHz Repeater
Repeater Frontside (Large)
Repeater Backside (Large)
Owner: Dan Thompson - N8WKM
Callsign: N8WKM
Frequency: 927.2625 TX / 902.2625 RX
CTCSS: 131.8 TX & RX
Location: West side of Grand Rapids, MI
Controller: Cat 300 DX
Receiver: Motorola MaxTrac 900
Exciter: Motorola MaxTrac 900, 300mw output
Amplifier: Glenayre (ex-paging amplifier)
Power Output: 400watts
Duplexer: TX-RX Vari-Notch pass/reject duplexer & DB Products Band Pass Filters
Antenna: DB Products 6dB Antenna
Power supply: Rack Mount 12amp Power Supply for controller and RX/exciter radios, 26V 80A Power Supply for Main TX Amplifier
Remote site: Shared 30A 12V Power Supply, Maxtrac 800 for RX, Maxtrac 900 for TX, Shared DB Products Dual Band RX antenna, Cellwave 11dB Yagi for TX
Other Info: 6' tall rack mount cabinet, Doug Hall 4RV Signal to Noise Voter,

This is version 2 of the N8WKM 902 Repeater operating at 927.2625Mhz Output and 902.2625 Mhz Input. The repeater requires 131.8 Tone for access. As the repeater says, "Welcome to the N8WKM Repeater. The time is ...."

The repeater was started with an idea after spending some time talking to other hams who were already using the 902-928Mhz band during the Dayton Hamvention 2002. Several people got excited about using 900Mhz and so began the the first 902Mhz amateur repeater in West Michigan.

David Buffington KC8HVT and I were the first to take the plunge that very Sunday afternoon by purchasing a pair of Motorola MTX-9000 portable radios. Within a couple of weeks several of the local hams were beginning to find and purchase suitable radios to use on 900Mhz. During this time I purchased a couple of Motorola MaxTrac 900 Radios and began the learning curve to make these radios operate within the 902 Ham bands. After many trials and errors, the new repeater was born. 900Mhz brought alot of new factors into repeater building for us. Primarily at 900Mhz small errors show up in big form. Also, the decision was made to follow the comercial use at these frequencies and use Narrowband Modulation of 2.5Khz. On top of that many of the ways that we have tested equipment in the past were no longer available. I had to purchase an RF meter that would work at 900Mhz, my choice was a Bird Model 43 along with elements in several different power ranges.

The repeater is currently operating from atop an apartment building in the Western part of Grand Rapids and shares facilities with the 145.410 Repeater. An approximated coverage map indicates excellent coverage. This map was made with a program called Radio Mobile. The program was given information about the height of the antenna, transmit power, reciever sensitivity, feedline and system losses, antenna type and gain as well as transmit and recieve frequencies. It uses terrain data and plots a coverage map. The map was produced for 10 Watts of power output from the repeater transmitter. The current configuration with the Glenayre amplifier feeds 325 watts to the 50' of 1/2 hardline that goes to the antenna.

At this point I would like to take a few keystrokes to thank all the people who have helped with make this repeater a reality. Sam Nabkey K8SN provided the cabinet and Hall Voter, Jeff Emery KI8BW who supplied the RackTrac custom enclosure to hold the main reciever and transmitter, tower climbers Doug Lemmen K8BBC and David Buffington KC8HVT, Mike Wolthuis KB8ZGL who found a boatload of 900Mhz MaxTracs, John Ruiz N8JPR, Bruce Sommer N8ODV, Jeff Nawrot N8JSN and all of the others who helped with carrying and moving equipment and were just there when they were needed to hand tools and parts to the rest of us. Also thanks to all of the people on the AR902Mhz yahoo list who helped with finding parts for the modifications and provided some technical info for getting started with the radios, especially Doug Bade who took time out to get me started on the right foot.

Current plans for the repeater are the addition of several remote recieve locations for top quality coverage. Design standards for the remote reciever and links are still in the works. Once again there will be a bit more learning curve as we are working with some things that we have not worked with in the past. Also in the plans is a change to a new RC-110 repeater controller by AH6LE. This controller has some great possibilities that I will be working on. This is going to be a great up and coming controller.

Currently we are working with several different radio models for use with the repeater. All of the radios that we use were made by Motorola and use 2.5Khz Narrowband FM Modulation. Top choices at this time are the Motorola GTX 900 series radios both mobiles and portables. These radios work sufficiently well with no hardware modification. Also in use are some Motorola MTX 9000 portable radios that also require no hardware modification for operation with the repeater. Next in line are the Motorola MaxTrac 900 and Spectra 900 radios. The Maxtracs require hardware modification that is not for the timid or uninitiated. I won't kid you the modifications require a steady hand and are time consuming. The Spectra radios also require some hardware modifications. At this time we have not made the modifications needed for this radio, but it looks like they will be similar to the Maxtracs.

All of the radios above are programable via software using a Radio Interface Box. The standard software will not work and I am not aware of any radio dealers that will program a radio into the ham bands for you. So, before you decide that you would like to join the people using 900Mhz you will need several items including a radio, a computer that will run in pure DOS (not a DOS window), a Radio Interface Box, and Software for programming the radio (Modified using a hex editor). These are just the minimums. You may also need to do hardware modifications that require removal and replacement of surface mount components about the size of the head of a straight pin.

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