147.285 MHz


London, OH

Photographs at the London Repeater Site

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Repeater Cabinet
The entire repeater (except for the 4-can duplexer) is installed a half-height Motorola equipment cabinet.  The Astron RS-35 Power Supply is located on the bottom.  Above that is the rack containing the 4 receivers and the voter (see photos below.)  Above that is the Hamtronics REP-200 Repeater Controller.  The large unit at the top is the 100W VoComm amplifier.
Receiver and Voter Rack
This is the rack containing the 4 receivers and the voter.  The rack is a Vector CMA13-20/90 Subrack and the individual modules are type EFP.  Two receiver modules are on each side, and the voter module is in the middle.
(When this photo was taken, only 3 receivers were installed, hence the blank panel near the center.)
Rcvr Rack - rear view
This is the rear view of the receiver and voter rack. 
Receiver Module
A receiver module.  Each receiver is installed in a separate module for improved shielding and isolation.  The large knob on the bottom is the volume control for a local speaker, and the smaller upper knob is the squelch control.  These receivers are very sensitive and selective - all measured less than 0.12uV sensitivity for 12 dB SINAD.
Receiver Module - rear
The rear view of a receiver module.  All of the connections are made at the rear panel.  The RCA jacks at the top connect the audio and COR signals to the voter.  12VDC is connected to the middle power jack.  The antenna connects to the SO-239 jack at the bottom.
Receiver Module - inside
An inside view showing the Hamtronics R-30x receiver mounted in the Vector EFP module. The volume and squelch controls had to be remounted on the circuit board in order to fit in the module.  All connections on the rear panel are bypassed with capacitors and filtered with ferrite beads. (Except for the antenna lead, of course!)
Voter Module
The DHE 4-RV Voter Card was also mounted in a EFP module.  Added to the front panel are 4 select switches to manually disable any of the receivers. At the lower right are 4 green LEDs to show which receiver is currently voted, and 4 red LEDs to indicate which receivers are receiving a signal.
Voter Module - inside
An inside view of the voter module.  The perf-board circuit on the left is the microcomputer the generates the CW reset beep indicating which receiver was voted the most.  The microcomputer is a PIC16F628.  The assembled program is 730 words long and uses 48 bytes of memory.
Tower at Madison County Hospital
This is the 140 ft tower at the Madison County Hospital.  Our repeater antenna is side-mounted at the 100 foot level. It is a Decibel Products DB-224 4-dipole array with 3 to 9 dB of gain.  Since it is side-mounted on the tower, the gain will vary depending on the direction - approx 9 dB gain towards the North and East , and about 3 dB to the Southwest.

The three UHF link antennas are about 15 feet below the  repeater antenna.  Each one points to its respective remote receiver in Sedalia, Plain City, and West Jefferson.
Link antennas on tower
A close-up view of the three UHF link antennas.  They are Cushcraft A449-6s yagi beams with about 10 dB of gain.

Copyright ©  2006 All rights reserved   Donald Kovalchik

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This page last updated January 30, 2006