N2CKH/R 6 meter Repeater System Configuration

System Duplexers:

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The most expensive (>$2,000 new) single item for many repeaters is the duplexer. It is the duplexer that allows simultaneous transmission and reception from a single antenna, using the same feedline. A pair of 6 meter duplexer's are large (usually six (6) feet tall) and heavey (over 200 lbs.) beasts compared to 2 meter units. However, I was lucky in that the DB Products units I got when I bought the WB2HAE system are small and relatively light and work great. See the photo below for size comparison to the rack mount 50 amp Astron at the bottom of the releay rack. Note that there is plenty of room to hold the PC, keyboard and monitor. (Does anyone have or know of a good source of either cheap VGA monitors in 19 inch rack configuration or 19 inch rack shelves ?)

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The cabinet that houses this set of duplexers is a wonderful thing, when you open the unit, the inside is immaculant, looks like they were just shipped from the factory.

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The DB Products 4030 series of duplexer provides a tremendous amount of rejection of other signals that may be on-site and on nearby frequencies (such as TV channel 2.). The four cavity Db Products duplexer consists of two band pass and two band reject cavities and tuning stubs. The transmitter is connected to one side of a "T" adapter via a 53.430MHz band pass and a 52.430MHz band reject cavity. The receiver is connected to the other side of the "T" via a 52.430MHz band pass and a 53.430MHz band reject cavity. The center of the "T" is connected to the coax which goes to the antenna.

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These duplexers use compact, quarterwave, high performance helical resonators that are interconnected in a band-reject configuration with double shielded cable. They isolate the receiver from the transmitter and reduce Tx noise in most tube or solid state systems. The duplexers are temperature compensated and provide power handling rated to 150 watts, even in extreme temperatures of -30 to +60 C. The insertion loss (transmitter to antenna) is better than -2 dB and the insertion loss (receiver to antenna) better than -2 dB. The Transmitter noise suppression at receiver frequency -80 dB and the Receiver isolation at transmit frequency -80 dB. The Maximum VSWR (referenced to 50 ohms) is 1.5:1 or better.

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A test was performed in which the transmitter was run at full 100w of power for one hour into a dummy load (good test of both the PA and duplexers) with no detectable rise in the cavity temperature.

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The cavities are reduced size for 6 meter operation, the self contained cabinet stands about three feet tall, an really protects the cavities, inside all is as new and shinny as the day they left the factory. These duplexers are not field retunes by the way, they were factory made and tuned and are labeled as such for the frequency pair 53.430/52.430 oringally purchased by WB2HAE.

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Since the Db-4030 duplexers can be tuned for a range of 30 to 54 Mhz, for the benefit of anyone that may have set of these units that are NOT tuned to the frequency that wish to use them on here is the factory tuning information for reference.

Click here for DB-4030 tuning procedures

Just as an extra precaution I added a Common Mode Choke with a few turns of the 9913F around an Amidon core on the receive input from the duplexer to keep both the repeater output as well as my 6 meter weak signal RF from riding into the receiver on the coax shield.

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System Controller:

The system WB2HAE had consisted of an old Hamtronics controller. While not super high-tech, I have updated this to an RC-1000 repeater controller that is very reliable and offers a fair amount of versatility.

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It is interfaced to the Master II via a customer cable wired into a DB-25 connector. The cable type used is double shielded four pair with the shield non-current carrying as it is grounded to the Master II only. Currently a total of six (6) connections to the Master II are being made for COS, PTT, Ground, Recieve Audio, Mic Audio, PL. In addition, a fused DC power cable is also wired to the DB-25 for power to the controller.

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It is the main controller for the system. It is to be interfaced to an IBM compatiable PC with AD/DA I/O board running MS-Windows with custom software by N2CKH for various auxilary control functions such as voice and DX-Cluster annoucements, SAME NOAA weather radio severe weather warnings and more. Also, an CSI CD-2 on an RS-232 will be used to decode mutliple CTCSS (a.ka. PL) and DCS (Digital Coded Squelch) signals and touch tones for control and signalling purposes.

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For the cost, size and weight, as far as I am concerned you can not beat the Diamond DP-GH62 5/8 wave over 5/8 wave co-linear ground plane antenna for a 6m Amateur repeater system . Its a relatively heavy duty aluminum base antenna that can be narrow banded and have its power rating increased by clipping a capacitor in the base, which I recommend for repeater operation.

At present, the antenna is 50 feet to the base of the antenna above ground (ground is 96 feet elevation above sea level) so its about 70 feet to the tip of the antenna in a pine tree in my backyard. It is fed with a way too long length of Belden 9913F low loss coax cable.

DP-GH62 Specifications:

Frequency: 6 Meters 50-54Mhz with capacitor, 52-54Mhz without capacitor
Gain: 6.0 dB gain
Power: 200 watts with capcitor, 500 watts FM without capacitor.
Connector: UHF (SO239)
Height: 21 feet
Weight: 6 lbs. (2.7 kg)
Wind Rating: 78 MPH

The Diamond replaced the Cushcraft AR-6 6m Ringo, which worked ok, but was not without problems.

AR-6 antenna specs:

Gain: 3.75db (3.0dbi)
Power Rating: 1Kw
Horizontal Radiation Pattern: 16 degrees
Antenna Pattern: Omni-Direcional, 360 degrees

System Power Supply:

The Astron RS-50M power supply is a proven design in mountain top use. It is capable of being run continuously at 40 amps, although is being used for about only 1/4 of this capability. It will also trickle charge the backup battery system that is planned to come online in the event of an AC power failure.

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The repeater draws about 650 milli-amps in standby mode, and ten amps when it is in transmit. It is planned to use a Sears Die-Hard marine battery has 71 amp-hours of storage capacity, thus with two full hours of repeater activity per day, the battery should be good for about five days of service. Power outages around here are never more than 6 hours in the fifteen plus years that I have lived in the area.

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Entire contents Copyright © 1999-2001 by Stephen B. Hajducek, N2CKH. All Rights Reserved Worldwide.