Bird Technologies 21-87A-11-xx-T Series-Manual - Manual (Page 23)

TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 17
short circuit. This loop is only used once in the bot-
tom cavity of the T-Pass stack. Detailed proce-
dures and illustrations follow on the next few
pages.
CAVITY LOSS SETTING PROCEDURE 1
This procedure uses precision rotary attenuators, a
signal generator and an RF Millivolt meter.
Required Test Equipment
1) Signal generator capable of producing a CW
signal level of at least -10 dBm with variable
output level capability at the frequency of inter-
est.
2) An RF voltmeter with a 0.001 Volt (-50 dBm)
scale and a 50 Ohm input adapter. Helper
Instruments RF millivolter used for this exam-
ple.
3) Rotary Attenuators, 1@ 0-1 dB in 0.1 dB incre-
ments. 1@ 0-10 dB in 1.0 dB increments. 1@
0-70 dB in 10 dB increments. JFW Industries
model 50BR-017.
4) Two 10 dB fixed attenuator pads with BNC con-
nectors. JFW Industries model 50F-010.
5) UG-914/U, BNC(F)-BNC(F), union. TX RX Sys-
tems' part # 8-5805.
6) UG-28A/U, N(F), N(F), N(F) tee.
7) UG-57B/U, N(M)-N(M) coupling.
8) Two, UG-201A/U BNC(F)-N(M) adapter. TX RX
Systems' part # 8-5814.
9) 50 ohm coaxial cable test leads with BNC male
connectors (high quality cable).
A spectrum analyzer may be used in place of the
RF voltmeter. However, the personnel doing the
work should fully understand the procedure and
understand the use of the analyzer for this applica-
tion. We have found it convenient to use test
cables with BNC connectors. They allow for more
convenient connection to test equipment and to
small attenuator pads. UG-201 BNC to N adapters
are used when connections to N connectors are
needed.
Procedure for T-Pass Loop
1) Set the signal generator for the desired operat-
ing frequency (within 1 MHz of operating fre-
quency) and for an output signal level of
approximately -10 dBm. Set the rotary attenua-
ZERO SET ZERO SET
0 0 0 0 0 0 0 0
1 2
3
3 4 56 7 8 9 10
Modulated
Signal Source RF Voltmeter
Rotary Attenuators
Set to Loop Reference Settings
0.1 dB/Div. 1.0 dB/Div. 10 dB/Div.
All cables are 50 Ohm
coaxial. Double shielded
cables preferred.
UG914/U
Female-Female
Connector
10 dB Attenuator Pads
50 Ohm Adaptor
Figure 12: Setting loop adjustment reference level.