HP 85662A, Руководство по устранению неисправностей и ремонту

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Attenuator-Bandwidth Filter and Bandwidth Filter operate at 21.4 MHz and
are variable in bandwidth from 3 to 3 MHz. The narrower bandwidths (3 through
30 are obtained from five synchronously tuned crystal filters; the wider bandwidths (100
through 3 MHz), from four synchronously tuned LC tank circuits (the bandwidths 10
Hz through 1 are obtained from 3 MHz Filter). The Bandwidth Filter assemblies
are on similar printed- circuit boards. has two LC filters and two crystal filters, and
has two LC filters and three crystal filters (A4861 Up Converter has a single 21.4 MHz
crystal that is used only for bandwidths These six crystals comprise a matched set
and must be replaced as such. The replacement assemblies are shipped without crystals, so
the crystals from the replaced boards must be used again.
Attenuator, 10 Amplifier
The 10 Amplifier is a common emitter amplifier with a gain of approx; 10
G
20
log G
287
=
20
log
3.16
3.16
10
For the lower gain settings of 0 and -10 (activated by and
respectively), additional collector resistance is switched in by CR3 or CR2, thereby lowering
the gain.
Input Buffer Amplifier
The unity gain Input Buffer Amplifier functions as a noninverting op amp. (See Figure 1.)
Figure 1. Input Buffer Amplifier, Equivalent Circuit
In the crystal mode (3 10 and 30 bandwidths), the amplifier includes Q2. The
biasing of the amplifier is independent of its ac (21.4 MHz) o eration but is very critical for
p
its proper functioning. If a malfunction occurs, the dc bias should be checked first.
1