The spectrum plot on the left reflects the frequency spectrum between the duplexer's receiver port and antenna port. The first marker (1) represents the repeater's transmit frequency (145.130 MHz), and the second marker (2) represents the repeater's receive frequency (144.530 MHz). The amount of attenuation is shown on the left vertical scale (10dB/division), while frequency is shown on the horizontal scale (200 kHz/division). As you can see, a -102.52 dB rolloff is observed at the transmitter's frequency. This prevents the transmitter frequency from desensitizing the repeater's receiver. This is a low pass filter. The overall receiver loss through the duplexer is -1.51 dB, and can be easily overcome with the implementation of a GaAsFET pre-amp on the receiver. The duplexers are manufactured by Sinclair Radio Laboratories, and consist of (3) highpass, and (3) low pass filters.

The spectrum plot on the right reflects the frequency spectrum between the duplexer's transmitter port and antenna port. The first marker (1) represents the repeater's transmit frequency (145.130 MHz), and the second marker (2) represents the repeater's receive frequency (144.530 MHz). As you can see, a -82.90 dB rolloff was observed at the receiver's frequency. Once again, this prevents the transmitter frequency from desensitizing the repeater's receiver. This is a high pass filter. The overall transmitter loss through the duplexer is -1.31 dB. The above test data indicates that the duplexers are tuned correctly, and require no further adjustment. All test data was taken on February 4, 1998, using a model 8714B Hewlett Packard RF Network Analyzer. Data was plotted using a Hewlett Packard Deskjet 850C. Special thanks goes out to Filter Design Engineer, Paul Kruczkowski of Axcera for his expertise in evaluating the duplexers.

  

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