Maintenance—492/492P Service Vol. 1 (SN B030000 & up)
Fig. 4-14. Test equipment setup for aligning the 829 MHz filter.
e.
Set the test spectrum analyzer Reference Level to
-2 0 dBm, Vertical Display mode to 2dB/div, Resolution
Bandwidth to 300 kHz, and Freq Span/Div to 20 MHz. Tune
the Center Frequency for a readout of 829.00 MHz on the
frequency counter.
g.
With the adjacent resonator (second) shorted to
ground, adjust the series capacitance by bending the tab so
the response on the spectrum analyzer display is centered
at 829 MHz (see Fig. 4-16A).
f.
Adjust the 1/4 wavelength lines in the filter in se
quence, starting with the resonator at the 829 1 MHz input
(see Fig. 4-15). Adjustment is made by shorting the adjacent
resonator to ground with a low inductance conductor, such
as a broad blade screwdriver, then bend the loop or tab of
the respective stub with a non-metallic tuning tool to change
the series capacitance of the resonator.
h.
Now move the shorting strap (screwdriver) to the next
resonator and adjust the tab of the second resonator for a
response as indicated in Fig. 4-16B.
i.
Remove the short from the third resonator and short
the fourth resonator. Adjust the third resonator for a re
sponse similar to that shown in Fig. 4-17A.
4-24
REVJUN 1983
