K3HKI Repeater System

Sponsored by the St Mary’s County Amateur Radio Association

The K3HKI repeater system operates on an assigned frequency of 146.64 MHz output and 146.04 MHz input.  A CTCSS tone of 146.2 Hz is required to access the repeater. There is a 440 MHz link for Control Operator use. Although equipped with CTCSS (aka “PL”), the repeater is considered an “Open” repeater, available for all to use. The coverage is approximately 25 miles for a 25 Watt mobile station and in the greater Lexington Park (5 miles) area for an “HT” (or “Portable, as the Fire/Police lads call it) type of transceiver.

The repeater is physically located on a 150 foot Navy owned tower, located in Hermanville Maryland, approximately 3.5 miles south of NAS Patuxent River. The primary user of the site is the Atlantic Test Range for their Range Safety Carrier equipment. Because of this, the site is equipped with an auto-start emergency generator, which will power the repeater after a short interval required to start the generator. 

The repeater consists of the following equipment:

  1. A Bridgecom BCR-50V Repeater.  50 Watts output. Self-contained AC power supply. It has provisions for a battery backup in the event of AC power main failure. This is not implemented, as we have emergency AC power at the site.
  2. A Phelps Dodge Six Cavity Duplexer to permit simultaneous use of one antenna by the transmitter and receiver.
  3. A Phelps Dodge Super Stationmaster Antenna, rated at 5.25 dbd gain, fed with 7/8 inch Andrew Heliax, hardline at 135 feet.
  4. A CAT-250 controller. Powered by 12 Volts DC from the BCR-50V.
  5. A Henry Radio continuous duty, commercial 130 watt repeater amplifier. Self-contained AC operated, 12 Volt/25 amp power supply.
  6. A Kenwood TM-241A 440 MHz link transceiver, with ground plane antenna at 75 feet. Powered by an Astron 12 Volt/7 Amp power supply.

There are two user functions enabled on the repeater for general use:

  1. Keying up the repeater and sending a DTMF (( aka “Touchtone”) code of “400”, will cause the repeater to read back the time.
  2. Keying up the repeater and sending 375 plus any other digits will read back those digits to test your keypad.

Operating notes:

  1. The repeater is equipped with a three minute time-out timer on the transmitter. During normal operation, when you drop your carrier and hear the courtesy tone, the timer has reset.  It is not necessary to let the repeater completely drop to reset the timer. A continuous transmission of more than 3 minutes will shut off the repeater.  After you stop transmitting you will not hear the familiar “courtesy tone”, and the repeater will reset and tell you that it is ready again.
  2. There is a 750 ms delay in the audio chain, so if you are also listening on another receiver or scanner, there will be a noticeable delay (echo). Just turn the volume down on the scanner.  This feature is to eliminate the annoying squelch crash heard on some repeaters.
  3. The controller is programmed to disable the Time Out Timer and the CTCSS during the scheduled, Tuesday night nets.  This permits announcements and lengthy transmissions without having to drop your carrier to “get another nickel” during the net. The control operator can also do this at any time.
  4. The control operator has the ability to control the repeater remotely. The repeater accepts control operator commands on both the 146.04 input frequency or on the 440 MHz link frequency. He has the ability to turn the repeater on or off, enable/inhibit the need for PL and, and enable/disable the timeout timer. Some programming inputs are also accepted.
  5. The repeater is set to transmit the 146.2 Hz CTCSS/PL tone on the 146.64 output frequency. You may hear this low frequency hum at a low level on your radio. The deviation on the tone is about 0.6 KHz and the normal voice deviation is about 3.5 to 4 KHz. This allows you to program your radio to only open the squelch upon receipt of the correct tone. This will keep other 64 repeaters (Richmond VA, Frederick MD, Pine Mountain PA, etc.) from opening your squelch during band openings. One downside to this is that you will not hear someone calling you on 64 simplex or if the backup repeater, which uses a different PL tone, is being used.

The current “techies” are Pete, WA3UMY and Tom, W4OKW.  It wouldn’t hurt to have another one or two on the committee.

Repeater duplexer (which allows the repeater to transmit and receive on the same antenna at the same time). The black box on top is the repeater itself, and the small white box on top of that is the repeater controller.
The current setup on the left with the Duplexer in the cabinet with the repeater on top of it and the repeater controller on the very top. The repeater and repeater controller will be placed (racked) into the cabinet on the right soon.
The tall antenna on the lower right of the tower is the repeater antenna. The short antenna above it is for a UHF control link that will go into place soon.