Bird Technologies 21-87A-11-xx-T Series-Manual - Manual (Page 25)

TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 19
reading is greater than the reference level, the
loop will have to be rotated so that the calibra-
tion mark on the loop points to a slightly higher
number on the calibration index label. Con-
versely, if the meter reading is less than the ref-
erence, the loop will have to be rotated so that
the index mark points to a slightly lower number
on the calibration index. Loosen the three loop
locking screws and rotate the loop so that the
index mark is moved to the next higher or lower
calibration tag number as needed and tighten
the 3 locking screws. Note that tight screws are
necessary for accuracy.
8) Repeat steps 6 and 7 until the minimum meter
reading is equal to the reference level from step
3. Rotation of loops will change the cavity fre-
quency slightly.
9) The Bandpass loop should be installed with the
connector up and the ground point circle ori-
ented toward the center of the cavity as shown
in Figure 14.
10) Remove the short circuit stub from the T-Pass
loop.
Procedure for Bandpass Loop
1) Maintain the previous signal generator settings
and set the rotary attenuators for the proper set-
ting as shown in table 4 for the Bandpass Loop.
2) Connect the test leads together through the
female union and adjust the range switch and
the zero set on the voltmeter for a reference
level (A level of 2 on the 0 to 3 scale is conve-
nient) on the meter. See figure 12. The genera-
Modulated
Signal Source RF Voltmeter
Rotary Attenuators
Set to Loop Reference Settings
0.1 dB/Div. 1.0 dB/Div. 10 dB/Div.
50 Ohm Adaptor
UG-28A/U
UG-57B/U
Bandpass
Loop
10 dB Pad 10 dB Pad
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.
Figure 14: Setting the Bandpass loop using step attenuators.