User's Manual

61-38-05 UserMan page 26 of 38
TXRX Systems Inc. Manual 7-9408-1.2 07/25/05 Page 26
b) From the
Mode Menu
, "STORE" the above
trace.
c) Switch to the
Display Menu
and select "REF".
6) Connect the leads to the cavity as shown in fig-
ure 16 and use a tuning tool or small screw
driver to engage the notch tuning capacitor and
rotate it to obtain maximum attenuation at the
notch frequency.
7) Tighten the cavity main tuning locking nuts.
The cavity may be put back into the repeater ampli-
fier.
Notch Filters
The notch filter passes a relatively wide band of
frequencies while rejecting (notches out) a very
narrow band of frequencies. They are used to
improve the skirt selectivity of associated band-
pass filters. These cavity filters are two inch
square, helical type resonators that include a tun-
able notching section, refer to
Figure 17
. These fil-
ters are pretuned and require no adjustment unless
they have been damaged and repaired or tam-
pered with in some way. They are passive devices
that require no maintenance.
REQUIRED EQUIPMENT
Due to the sensitivity of the adjustments, it is
strongly recommended that the proper equipment
be used when tuning the individual filters, other-
wise the filter should be sent to the factory or an
authorized representative for retuning. The follow-
ing equipment or it's equivalent is recommended in
order to properly perform the tuning adjustments.
1) IFR A-7550 Spectrum Analyzer / Tracking Gen-
erator combination.
2) Eagle Model RLB150BN3 Return Loss Bridge
(35 dB directivity).
3) Double shielded coaxial cable test leads
(RG142 B\U or RG223/U).
Analyzer
Input
Generate
Output
+30
+40
+20
+10
0
-10
-20
-30
-40
2" Square VHF
Pseudo-Bandpass Filter
Tracking Generator
Tune
Figure 16
: Tuning the Pseudo-bandpass filter
for maximum attenuation.
Sliding Main
Tuning Rod
(Notch)
Main Tuning
Lock Nut
Passband
Tuning
Capacitor
Input/Output
Connectors
Figure 17
: The Notch filter.