Data Sheet Chapter 4

3-kW UHF Transmitter Chapter 4, Detailed Alignment Procedures
835-3, Rev. 0 4-13
For major tuning, such as changing the notch depth or moving the notch frequency
more than 1 MHz, the outer conductor and the center conductor of the trap section must
both be moved. This requires an RF sweep generator to accomplish. Apply the sweep
signal to the input of the trap filter and monitor the output. Loosen the clamp holding
the outer conductor in place and make the length longer to lower the frequency of the
notch or shorter to raise the frequency of the notch. Loosen the center conductor with
an Allen wrench and move it deeper for a lower-frequency notch or out for a higher-
frequency notch.
These adjustments must both be made in order to change the notch frequency; the
effects of these adjustments are shown in Table 4-1. Moving only the center conductor
or the outer conductor will effect the notch depth in addition to the center frequency.
The variable that is being adjusted with this procedure is the length of the center
conductor inside the trap filter. The gap between the trap and the main line should not
be changed. Moving only the inner or the outer conductors by themselves will affect
both the gap and the notch depth.
To effect the notch depth only, both sections will have to be moved. The notch depth is
controlled by the gap between the center conductor and the trap section. This gap also
has an effect on the center frequency. To deepen the notch, shorten the outer conductor
and pull the center conductor out until the notch is back in the same place. Move the
sections in the opposite direction to make a shallow notch.
Table 4-1. Effects of Tuning the Output Trap Filter
ADJUSTMENT EFFECT
Lengthening outer conductor only Notch frequency up, shallower notch
Shortening outer conductor only Notch frequency down, deeper notch
Inserting inner conductor deeper Notch frequency down, deeper notch
Inserting less inner conductor Notch frequency up, shallower notch
Tuning bolt in Notch frequency down
Tuning bolt out Notch frequency up
Moving both inner and outer conductors
to keep the same gap inside
Center frequency moves notch stays the
same
After tuning has been completed, tighten the clamp and the Allen screws that hold the
conductors. Use the fine-tuning bolts to bring in the frequency. The final tuning
adjustments should be completed with the transmitter driving the output trap filter for
at least one hour to allow for drift during the warming-up period.
This completes the alignment procedures for the bandpass filter and output trap filter
assembly.