Service
PRINCIPLES
OF
OPERATION---SERVICE SHEETS
2A
AND
26
Model
8903B
SERVICE SHEETS 2A AND 2B---A2A1 and A2A2 Weighting Bandpass and High-Pass Filter
Assemblies
PRINCIPLES
OF
OPERATION
The Weighting Bandpass and High-Pass Filter Assemblies (A2A
I
or A2A2) are optional audio filters which plug
onto the A2 Inpiit Amplifier Assembly
to
filter the signal before being measured by the Pre-Notch RMS/Average
or Outpiit RMS/Average Detector. In general the filters are quite similar. The filters are active types composed
of miiltiple high-pass, low-pass, and bandpass sections. The CCITT Weighting Filter will serve
as
an
example.
The CCITT Weighting Filter (sometimes referred to as
a
psophometric filter) is
a
complex collection of
poles
and zeros which produces
a
bandpass response.
U
1
A,
U
1
B,
U
ID,
and their associated resistors and capacitors
have low-pass responses.
UIC
and its associated resistors and capacitors have
a
bandpass response.
U9
on the
A2 Input Amplifier Assembly (see Service Sheet 2) and its associated resistors
and
capacitors have
a
high-pass
response.
R8
and C5 is
a
single-pole, passive low-pass filter.
C10
and
R14
is
a
single-pole, passive high-pass
filter.
R4
adjusts the overall filter gain.
Some filters, siich
as
the
“A”
Weighting Filter, have
a
resistor (R15) which increases the sensitivity
of
the Input
Range Detector. (See Service Sheet 2.)
8B-24
To Next Page
Loading...
