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Duplexer for 2 m amateur repeaters
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As we know, in order to get maximum repeater sensitivity with frequency spacing of 600 kHz, an isolation of about 90dB between receiver and transmitter is needed.
Receiver should be protected from the influence of both high-power carrier and transmitter noise. To accomplish the first statement the receiver circuit is equipped with filters. Noise reduction filters are installed directly into the main source of the noise – transmitter. These filters may be interconnected. This assembly is known as duplexer. The duplexer allows receiver and transmitter to share simultaneously one common antenna.
Operating frequency band (144-146 MHz) is enabled by quarter-wavelength (λ/4) square-shaped coaxial resonators with side of 4″ (100 mm). There are 6 such filters. Main resonator is made of copper. The resonator is firmly screwed to upper cover to eliminate energy loss. Case of the resonator is made of aluminum and by extrusion molding. Frequency adjustment is enabled with specifically designed capacitor. Its knob is located at the side panel of the resonator. After making adjustments the capacitor is locked with a nut. As you can see, this resonator has no thermal compensating screw made of Invar®, as distinguished from DPRE and DPR professional duplexers. But it makes no difference if a duplexer is located in a heated space. A thermal drift of +/-15 degrees does not affect the operation of the resonator. Therefore, such solution helps to reduce the duplexer production costs.
30 dB signal rejection in each resonator is achieved by a coupling loop and cable capacitor. We have eliminated traditional movable coupling loops with variable interaction factor due to amateur repeaters having 600 kHz constant fixed frequency spacing. Such design allows reducing cost and provides all required electrical characteristics. Filters are interconnected by Habia's semi-rigid 0.141″ cable with fluoroplastic insulation. Cables are soldered directly without connectors. Thus, we gain savings in both cost and power energy.
| | Electrical specifications
Model |
DPRH4-6-2M
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Operating frequency band, MHz |
144-148
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Insertion loss (adjustable) not more, dB |
1.7
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Frequency separation TX/RX (min), kHz |
600
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Impedance, Ohm |
50
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Isolation, not less, dB |
90
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VSWR, not more than |
1.5
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Input power, not more, W |
100
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Temperature range, °C |
from +5 to +35 |
Cavity electrical length |
1/4λ
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Mechanical specifications
Model |
DPRH4-6-2M
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Diameter, mm (ins.) |
105x105 (4")
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Weight, kg |
24
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Connector |
N-female
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Mount to 19-inch rack |
present
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Length/Width/Depth, mm |
700x480x215
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Typical duplexers response curves.
DPRH4-6-2M
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