Honeywell XK516D1 Maintenance Manual page 70

Honeywell
COMPONENT MAINTENANCE MANUAL
PART NUMBER 964-0452
5 ALC Amplifier
The DIODES signal reaches the first phase-boosting section, provided by N4-C,
via operational amplifier, N4-D, which is connected with v = 1 as a noninverting
amplifier. The amplification from R15 and R104 results in v = –2 for direct volt-
age. For high frequencies on the other hand, C8 functions like a short-circuit,
and the amplification from R7 and R104 results in v = –0.068, whereby the
°
phase shift is 180 both with direct voltage and high frequencies.
The second phase-boosting section, provided by N4-A, has a direct voltage am-
plification of v = –15 (R110/R103). With medium frequencies, the resistance of
C3 becomes steadily lower, consequently making R6 active, as a result of which
the amplification decreases. With very high frequencies, C9 and C3 have a neg-
ative feedback effect, causing the amplification for high frequencies to approxi-
°
mate v = 0. The phase shift remains at approximately 135 , however, even with
high frequencies.
The decrease in amplification at high frequencies with simultaneous phase
boosting is essential for the stability of the entire control circuit, since a high di-
rect voltage ring amplification is necessary for minimum control deviation during
stationary operation; similarly, the actuator and the control system must be quick
in order to permit the output power to reduce in a short time.
Diodes, V10 and V11, are required so that the negative voltage present at the
DIODES signal with a control reset does not saturate operational amplifiers,
N4-C and N4-A, and furthermore, so that capacitors, C8 and C3, are not nega-
tively charged at the end of the reset.
Operational amplifier, N4-B, quickly charges hold capacitors, C57 and C59, to
the positive peak value of the voltage at N4.2 via diode, V36, and resistor R100.
Operational amplifier, N5-B, serves only as driver with v = 1, and therefore,
passes on the voltage at the hold capacitors to provide the ALC signal.
This ALC signal acts on a voltage-controlled attenuator with a transconductance
of approximately –7dB per volt in Amplifier Board, A31, and thus regulates the
overall RF gain of Amplifier Board, A31.
During voice communications, the overall gain, and therefore, also the ALC volt-
age, must be kept constant during short breaks in speech, and the amplifier set
to maximum gain only with longer pauses. With the amplifier driven to full output,
a positive voltage peak is present at N4.10 with every voice peak that would re-
sult in the 400W output power being exceeded, and the operational amplifier,
pep
N5-D, connected as a comparator goes to approximately –13V at its output.
This results in capacitor, C96, being charged to about –12V via R213 and V49,
and transistor, V50, is disabled. Consequently, hold capacitors, C57 and C59,
are not discharged.
If, however, no or only minimum output power is present during a speech pause
in SSB transmission mode, the N4.10 voltage goes towards the lower limit val-
ue, the output of comparator N5-D goes to approximately +13V, whereby diode,
V49, is disabled, and capacitor C96 is charged via R214 with 100ms time con-
stant to +5V. If the threshold voltage of about 2V is exceeded at V50, the latter
begins to conduct and discharges hold capacitors, C57 and C59, via R101 and
R106 with a time constant of 4 seconds.
1I.B.1516A Page 62 Page 40
23-12-01
Mar 30/01