Bird Technologies Group 5PI613805 Manual De Usuario

either the transmission or reflection response
may be unavoidable.

Bandpass Filters
The bandpass filters pass one narrow band of fre-
quencies (the passband) and attenuate all others
with increasing attenuation above and below the
pass frequencies. The insertion loss setting deter-
mines the filters selectivity and maximum power
handling capability. Insertion loss is set at the fac-
tory.

Cavity tuning follows a two step process. First the
cavity is temporarily disconnected from the system

and rough tuned, this will ensure the response
curve is very close to it's ideal. Next the cavity is
reconnected to the system and fine tuned. This is
done in large systems such as the model 61-38-05
in order to eliminate any slight distortions which
could result from interactions with other cavities.

The pass frequency is the only field adjustable
parameter found in the individual Bandpass reso-
nant cavity filters. Adjustment of the tuning rod on
these filters will allow the passband to be centered
at the desired frequency. The insertion loss of each
cavity is not field adjustable.

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 with optional

tracking generator installed.

2. 7/16” wrench.

3. Double shielded coaxial cable test leads

(RG142 B/U or RG223/U).

4. Female union (UG29-N or UG914-BNC).

TUNING PROCEDURE
The following is an outline of the general proce-
dure.

1. Turn off the system power and disconnect the

cables that are attached to the cavity. 

2. Setup the analyzer / generator for the desired

frequency and bandwidth (center of display)
and also a vertical scale of 2 dB/div. Set the
sweep width of the display to 100 KHz.

4. A zero reference must first be established at the

IFR A-7550 before making measurements. This
is accomplished by temporarily placing a
"female union" between the generator output
and the analyzer input.

5. The flat line across the screen is the generator's

output with no attenuation, this value will
become our reference value by selecting the

4 Section 

Helical Preselector

Analyzer
Input

Generate

Output

+30

+40

+20

+10

0

-10

-20

-30

-40

Bridge

50 ohm Load

Figure 12: Observing preselector return loss.