Bird Technologies 15-88-01 - Manual (Page 5)

TX RX Systems Inc. Manual 7-9150-2 07/19/07 Page 1
GENERAL DESCRIPTION
The 4" Vari-Notch® cavity filter is designed to pass
a relatively narrow band of frequencies (pass-
band) while simultaneously rejecting a wide band
of frequencies (rejection notch). A variety of mod-
els are available that cover the range of frequen-
cies from 132 to 960 MHz. The por tion of the
frequency range that each model will tune across is
determined by the cavity's physical length.
Two types of 4" Vari-Notch filters are available, low-
pass and highpass. Lowpass filters have the pass-
band below the notch frequency while highpass
filters have the passband above the notch. The
cavity itself remains identical for both types. Figure
1 shows the response curve of a lowpass filter.
There are two adjustable parameters in a 4" Vari-
Notch filter including the passband frequency and
the rejection notch frequency. Both of these
parameters are labeled on the response curve
shown in figure 1. All of the physical components
of the filter are labeled in Figure 2, with the adjust-
able parts shown in emboldened italics. The tuning
rod is used to adjust the passband while a variable
capacitor is used to adjust the rejection notch.
TUNING
Required Equipment
The following equipment or it's equivalent is rec-
ommended in order to properly perform the tuning
adjustments for the 4" Vari-Notch filter.
1. IFR A-7550 Spectrum Analyzer with optional
Tracking Generator installed.
2. Eagle Return Loss Bridge (model
RLB150N3A).
3. Double shielded coaxial cable test leads
(RG142 B/U or RG223/U).
4. 50 Ohm load, with at least -35 dB return loss
(1.10:1 VSWR).
5. Insulated tuning tool (TX RX Systems Inc. part#
95-00-01).
6. 1/4" open-ended wrench.
Analyzer
Input Generate
Output
0
+10
-10
-20
-30
-40
-50
-60
-70
Passband
Rejection Notch
Figure 1: Spectrum Analyzer/Tracking Generator display of the lowpass 4” Vari-Notch filter.
Response curve shown for model number 15-52-01 (215-250 MHz)