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Bird Technologies 21-87A-11-xx-T Series-Manual User Manual

Page 28

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TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 22

and let it warm up for at least 30 minutes if this
has not been done.

3) Note the Reference Notch Depth value for the

Bandpass loop assembly to be adjusted from
table 4.

4) Set the spectrum analyzer for the frequency of

the channel of interest (within 5 MHz of actual
operating frequency).

5) If the Reference Notch Depth is 8 dB or less

then set the display for a vertical range of 2dB/
div otherwise set it for 10dB/div.

6) Temporarily connect the test leads from the

spectrum analyzer together through a UG-914
BNC union to set the zero reference. Make sure
to use the 10 dB pads which should remain on
the test cables for all measurements.

7) Connect a UG-28 tee and a UG-57 coupling to

the bandpass loop as shown in figure 16.

8) Connect the test leads from the spectrum ana-

lyzer to the tee connector as shown in figure 16.

9) Adjust the cavities main tuning rod so that a

rejection notch appears in the center of the dis-
play.

10) Loosen the three loop locking screws and

rotate the loop assembly to obtain the refer-
ence notch depth from step 3.

The tightness of the locking screws
affects the depth of the rejection
notch slightly, it is usually necessary
to rotate the loop for a notch depth
that is slightly less than the reference.

The Notch depth will tend to increase slightly as all
three locking screws are tightened.

NOTE

10 dB Pad

10 dB Pad

UG-28A/U

UG-57B/U

Bandpass
Loop

Previously calibrated
T-Pass Loop 3-1268
short circuit removed.

Small Circle on
Bandpass Loop
indicates ground
end of loop and
should be oriented
as shown.

Spectrum Analyzer

Bird SignalHawk

Signal Generator

Figure 16: Setting a Bandpass loop for a specific cavity insertion loss.