2
6
2
with C36 for Q2. The outputs of each transistor pair are transformed into combined signals by
coaxial baluns Z3 and Z4. These two signals are then combined again by 90
E
hybrid HY2 and
delivered to the module output at J2. Output matching and coupling for each transistor pair are
furnished by capacitors C8-C12, C62 for Q1, and C20-C24, C63 for Q2. Inductors L1 through L6
are employed as RF chokes with the remaining capacitors used for RF bypass.
If a fault occurs in either transistor pair, the difference in power at the hybrid HY2 inputs will create
an imbalance causing excessive power to appear at the HY2 ISOlation port. To monitor this fault,
a power detection circuit, centered around diode CR1, transforms this excess power into a DC
voltage which appears as a TTL high at terminal E11. On the Indicator Circuit (PC3) board this
logic level high will change the front panel AMPL 1 status LED from green to red.
2.1b
UHF Notch Filter:
Schematic Diagram N/A
ò
A3FL1
Insertion Loss
0.5dB maximum
Notch Depth
!
12dB minimum
Notch Frequency
Visual Carrier
!
4.5MHz
Aural C4.5MHz
This filter is a tunable two-section notch filter that removes the spurious products created through
common amplification 4.5MHz below the visual carrier and above the aural carrier of the
transmitted channel. Each notch has a minimum attenuation of 12dB, with the insertion loss of the
passband at 0.5dB maximum.
2.1c
Metering Coupler:
Schematic Diagram 10199178/Rev 52
ò
A3DC1
Insertion Loss (J1-J2)
<0.5dB
FWD Coupling (J1-J3)
30dB
REFL Coupling (J1-J4)
30dB
The Metering Coupler is a four port device designed to provide forward and reflected RF samples
to the Metering Detector (A2) with minimal loss to the output signal. The RF signal from the Notch
Filter is applied to the coupler’s input port (J1) and exits the coupler at J2 with a maximum of 0.5dB
of loss. A
!
30dB sample of the signal’s forward power is provided at J3, and a
!
30dB sample of
the reflected power is provided at J4. These two signals are connected through 6dB attenuators
(AT3, AT4) to the metering detector which then provides DC signals, proportional to the amplifier’s
output power, to the Control Board, AGC circuit, and Metering Switch.
