Honeywell Bendix/King KX 165A, Maintenance Manual

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BENDIX/KING KX 165A
Page 4-38 15610M00.RCD Rev 0, Jun/2000
4.3.4 GLIDESLOPE RECEIVER Fig 6-29
4.3.4.1 General
The Glideslope Board contains a receiver that may be tuned throughout the Glideslope frequency
band of 329.15 to 335.00 MHz. The Glideslope operating frequency is paired with a selected Lo-
calizer frequency (Reference
Table 4-2 .). The radio selects the proper Glideslope frequency
based upon the Localizer channel. Digital and analog I/O comes from the VHF Main board via a
12 pin ribbon cable. The RF input comes in externally through the antenna connection on the back
of the radio. There is a rear edge card connector that is used to output analog converter signals
necessary to drive an external indicator. The receiver gets its synthesizer tuning, and DC power
from the VHF Main board.
4.3.4.2 Variable Gain RF Amplifier
Q6 is an N-channel depletion type dual gate MOS-FET that is the active component in the Variable
Gain RF Amplifier. The RF AGC voltage is applied to one of its gates, and controls the amount of
RF gain through the amplifier. The RF AGC voltage can vary from 0 to 8.5 V, resulting in a gain
variation of +20 dB to -30 dB of gain. The full range of gain adjustment occurs as the input RF
power varies from -90 dBm to -50dBm. A moderate amount of preselection filtering is accom-
plished in the tuned matching circuits of L1/C48/L5 and C49/L6/C7. C50 forms a 166MHz series
resonant circuit with C48/L5. This series resonant circuit filters out the 1/2 channel frequency so
that the out of band response is minimized.
4.3.4.3 13 dB Attenuator
The 13 dB RF Attenuator reduces the amount of RF power input to later stages. Reducing the
signal level improves the crossmod performance of the MMIC RF Amplifier and the Mixer. Excess
RF power exists because of the Mixer LO to Antenna Port reverse isolation requirement necessi-
tating the use of the RF MMIC Amplifier.
4.3.4.4 RF MMIC Amplifier
This is a high reverse isolation silicon MMIC amplifier with a gain of 20 dB in the GS frequency
band.
4.3.4.1.5 16 dB Attenuator
The 16 dB RF Attenuator reduces the amount of RF power input to the Mixer. Reducing the signal
level improves the crossmod performance of the Mixer. Excess RF power exists because of the
Mixer LO to Antenna Port reverse isolation requirement necessitating the use of the RF MMIC Am-
plifier.
111.15 331.55
111.30 332.30
111.35 332.15
111.50 332.90
111.55 332.75
111.70 333.50
111.75 333.35
111.90 331.10
111.95 330.95