Bird Technologies 28-88-04B - Manual (Page 11)

TXRX Systems Inc. Manual 7-9176-4 06/23/04 Page 7
1. Reassemble the duplexer by reinstalling the cav-
ities and interconnect cables in their original
locations.
2. The passband for the channels are fine tuned
first, in a manner very similar to tuning a single
cavity.
3. A zero reference for return loss must be estab-
lished at the IFR-7550. Connect the RLB to the
analyzer / generator as shown in figure 3.
4. Set-up the analyzer / generator to the desired
frequency (center of display) and for a vertical
scale of 10 dB/div.
5. Do not connect the RLB to the duplexer at this
time, leave the "load" port on the bridge open.
This will supply the maximum amount of
reflected energy to the analyzer input.
6. Insure that the IFR A-7550 menu's are set as
follows:
DISPLAY - line
MODE - live
FILTER - none
SETUP - 50 ohm/dBm/gen1.
7. The flat line across the screen is the return
loss curve. Select the "MODE" main menu item
and then choose the "STORE " command.
8. Next select the "DISPLAY" main menu item
and choose the "REFERENCE" command.
This will cause the stored value to be displayed
at the center of the screen as the 0 dB refer-
ence value.
9. Connect the "load" port on the RLB to the
equipment port of the channel to be fine tuned.
Terminate the duplexers antenna connector
with the 50 ohm load. The equipment port of
the remaining duplexer channel is left discon-
nected, refer to Figure 6.
10. The display will now present the combined
return loss curve for all of the cavities in the
channel. The channels passband is that fre-
quency range over which the return loss is 15
dB or greater.
11. Fine tune the passband (for maximum return
loss) for the entire channel by gently adjusting
the positions of the tuning rods, moving
between cavities as required. Once the desired
response is obtained "lock" the tuning rods into
place by tightening the 1/4" shaft lock nuts on
each filter.
12. Move the cable from the RLB's "load" port to
the equipment port of the other channel. This
will allow the remaining duplexer channel to be
fine tuned. Reset the analyzer / generator cen-
ter frequency. Repeat steps 10 and 11.
GENERATE
OUTPUT
ANALYZER
INPUT
10
0
-10
-20
-30
-40
-50
-60
-70
dBm
40 0 10
300
dB ATT GEN dBM MSEC
KHz RES KHz/DIV
500
MHz
4" DIAMETER
VARI-NOTCH
FILTER
Figure 5: Checking the rejection notch.