Bird Technologies 21-87A-11-xx-T Series-Manual - Manual (Page 26)

TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 20
tor output level may also be adjusted slightly if
convenient.
3) Set all three attenuators for 0 dB but leave them
in the circuit.
4) Connect a UG-107 Tee and the UG-57B/U to
the Bandpass loop as shown on figure 14. Then
connect the test leads as shown. Make sure the
short circuit stub has been removed from the T-
Pass loop.
5) Loosen the main tuning rod locking screw (see
figure 8) and slowly slide tuning rod in or out to
obtain a dip (minimum voltage) in the meter
reading which indicates cavity resonance. Use
the fine tuning control to maximize the dip (the
fine tuning rod should not be full in or out which
would indicate that slight adjustment of the
main tuning is necessary). Note the meter read-
ing.
6) If the meter reading is greater or less than the
reference level from step 2, the bandpass loop
rotation will have to be adjusted. If the meter
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.
7) Repeat steps 5 and 6 until the minimum meter
reading is equal to the reference level from step
3. Rotation of loops will change the cavity fre-
quency slightly.
8) Make sure that all the loop locking screws are
tight. The cavity loops are now set and the cav-
ity should now be tuned to the desired fre-
quency as outlined elsewhere in this manual.
CAVITY LOSS SETTING PROCEDURE 2
This procedure uses a spectrum analyzer, signal
generator, and fixed attenuator pads.
Required Test Equipment
1) Spectrum Analyzer and a signal generator.
2) Two 10 dB fixed attenuator pads with BNC
connectors. JFW Industries model 50F-010.
3) UG-914/U, BNC(F)-BNC(F), union. TX RX Sys-
tems' part # 8-5805.
4) UG-28A/U, N(F), N(F), N(F) tee.
5) UG-57B/U, N(M)-N(M) coupling.
6) Two, UG-201A/U BNC(F)-N(M) adapter. TX RX
Systems' part # 8-5814.
7) 50 ohm coaxial cable test leads with BNC male
connectors (high quality cable).
We have found it convenient to use test cables with
BNC connectors. They allow for a more convenient
connection to test equipment and small attenuator
pads. UG-201 BNC to N adapters are used when
connections to N connectors are needed.
Procedure for T-Pass Loop
1) Remove the screws that hold in the bandpass
loop assembly; remove the assembly; invert it
and place it back into the cavity. The coupling
loop will be visible. Install and tighten the three
locking screws.
2) Connect the test leads to the spectrum ana-
lyzer; turn it on and let it warm up for at least 30
minutes.
3) Connect the 10 dB attenuator pads to the test
leads. They will remain connected for all subse-
quent measurements.
4) Note the Reference Notch Depth value for the
T-Pass loop assembly to be adjusted from the
chart, see table 4.
5) Set the spectrum analyzer for the frequency of
the channel of interest (within 5 MHz of actual
operating frequency)
6) 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.