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Duplexers for 2 m amateur repeaters
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DPRE4-6V
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To ensure a large range for the operation of VHF repeaters besides providing the adequate height of the equipment mounting it is needed to achieve an actual high sensitivity of the repeater's receiver. The data that is written down in its technical passport still does not mean that it is capable to receive just such weak signals in real conditions. Let us consider what can prevent the receiver of the repeater to recognize the weak signals from far distanced radio-stations.
A repeater always operate in duplex regime. This means that while the receiver is operating the transmitter simultaneously irradiates a high power just nearby. And any transmitter always irradiates both the carrier frequency and the auxiliary noise.
Even in the case that the transmitter meets the highest technical requirements and possesses the capability of suppression of out-of-band irradiations of more than 70 dB, this is not yet sufficient for not preventing the receiver to catch the distant stations. The reason for this is that the frequency separation for the amateur repeaters is only 600 kHz for 145 MHz and the own selective properties of the transmitter do not allow to eliminate completely this transmitter's noise.
Just in the same way the input circuits of the receiver are not capable to completely eliminate the influence of the carrier frequency of the transmitter. In the case if the receiver's and the transmitter's antennas are arranged closely to each other the blocking of ultra-high frequencies and the partial loss of the sensitivity take place.
In order to eliminate these two drawbacks the influence of noise and the influence of the carrier frequency of the own transmitter of the repeater we have to apply an additional selective devices. And because of the fact that the frequency separations TX/RX are very small the requirements to the Q-factor of these devices have to become higher. That is why special high-quality coaxial cavities have to be applied which possess the different selective capabilities.
| | Electrical specifications
| Model |
DPRE4-6VL
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| Operating frequency band, MHz |
144-148
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| Insertion loss (adjustable) not more, dB |
1.3
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| Frequency separation TX/RX (min), MHz |
0.4
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| Impedance, Ohm |
50
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| Isolation, not less, dB |
97
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| VSWR, not more than |
1.5
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| Input power, not more, W |
300
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| Temperature range, °C |
from -30 to +60
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| Cavity electrical length |
1/4?
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Mechanical specifications
| Model |
DPRE4-6VL
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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.
DPRE4-6VL
Also read:Technique of fine tuning of duplexer DPRE4-6VL which has been adjusted at a factory, but undergone out of adjustment.(PDF)
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