User's Manual

61-38-05 UserMan page 24 of 38
TXRX Systems Inc. Manual 7-9408-1.2 07/25/05 Page 24
"MODE" main menu item and choosing the
"STORE" command. This will store the flat-line
value in the analyzer's internal memory.
6. Next select the "DISPLAY" main menu item and
choose the "REFERENCE" command. This will
cause the stored value to be displayed on the
screen as the 0 dB reference value
.
7. The resonant frequency of the filter is checked
by connecting the tracking generator to the
input of the cavity filter assembly while the
spectrum analyzer is connected to the output,
as shown in
Figure 13
.
8. Insure the IFR A-7550 menu's are set as fol-
lows:
DISPLAY - line
MODE - live
FILTER - none
SETUP - 50 ohm/dBm/gen1.
9. Adjust the pass frequency by setting the peak
(minimum loss value) of the response curve to
the desired frequency (should be the center-
vertical graticule line on the IFR A-7550's dis-
play). The resonant frequency is adjusted by
adjusting the tuning rod, which is a sliding
adjustment (invar rod) that rapidly tunes the fil-
ter's response curve.
Pseudo-Bandpass Filters
The pseudo-bandpass filter passes a relatively nar-
row band of frequencies and rejects (notches out)
a relatively wide frequency band. These cavity fil-
ters are two inch square, helical type resonators
that include a tunable notching section, refer to
Figure 14
. These filters are pretuned and require
no adjustment unless they have been damaged
and repaired or tampered with in some way. They
are passive devices that require no maintenance.
Female Union
Used to determine 0 dB reference
Analyzer
Input
Generate
Output
+60
+80
+40
+20
0
-20
-40
-60
-80
Tracking Generator
2" Sq. Bandpass
Cavity Filter
Figure 13
: Bandpass filter tuning.
Sliding Main
Tuning Rod
(Passband)
Main Tuning
Lock Nut
Rejection
Notch Tuning
Capacitor
Input/Output
Connectors
Figure 14
: The Pseudo-bandpass filter.