9-24 MTR3000 Radio Frequency Distribution System (RFDS) Equipment: Field Tuning Procedures
c. Fine Tuning
i. The 435–470 MHz band preselector is now roughly tuned to the required passband.
Refer to Figure 9-16 and Figure 9-17. The preselector performance will now be fine-
tuned to specification-required frequencies and levels.
Figure 9-16 Passband and return loss after rough tuning
Figure 9-17 Return loss
ii. In this process, make only small (less than 10°) adjustments. Working with each of the
tuning screws 2, 3, or 4 (one at a time), make slight adjustments in either direction while
observing the return loss curve. For example, turning one of the screws clockwise may
result in worse return loss such as shown in Figure 9-18 or better as shown in
Figure 9-19.
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