K89296
VHF Communication System Component Location 5C8
23-21-01 Figure 1 Jun 20/85
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
B. On GJ B-2509 thru B-2510, VHF control panels consist of two frequency selection knobs, a transfer switch, and a test button. Rotation of the two outer knobs sets up the frequency which appears in a window above the knobs. The outermost knob has 18 positions numbered 118 thru 135. The next knob has 40 positions numbered 0.00 thru 0.975. (The 0.005 digit does not appear in the window.) Any of 720 channels with 25-kHz spacing may be selected. The transfer switch is used to select the right or left set of frequencies. Pressing the TEST button disables receiver squelch circuits. If background noise increases, the receiver is operating properly.
C. On GJ B-2504 thru B2505, the VHF communication system controls consist of: a set of frequency selection knobs, a volume control and a test button. Rotation of the outer knob will set up the frequency which is then indicated through a window above the knob. The outermost knob has 18 positions numbered 118 thru 135. The next knob has 40 positions numbered 0.000 thru 0.97. (The 0.005-MHz position is not indicated in the frequency window.) Any of 720 channels with 25-kHz spacing may be selected on frequencies of 118.000 to 135.975 MHz. Pressing the TEST button disables receiver squelch circuits allowing an increase in background noise, thus indicating whether the receiver is operating properly.
D. On GJ ALL EXCEPT B-2504 thru B-2505 and B-2509 thru B-2510, the VHF communication system controls consist of: a dual set of frequency selection knobs, a volume control, a test button, and a transfer switch. Each section of the dual set of frequency knobs control the same VHF system. A different frequency may be set up on each section. By positioning the transfer switch to the left, the frequency set up on the left will be used by the VHF transceiver and a transfer flag will negate the right frequency window. Positioning the transfer switch to the right will cause the VHF transceiver to tune to the frequency set up on the right and the left frequency window will be flagged. Rotation of the two outer knobs will set up the frequency which is then indicated through a window above the knobs. The outermost knob has 18 positions numbered 118 thru 135. The next knob has 40 positions numbered 0.000 thru
0.97. (The 0.005-MHz position is not indicated in the frequency window.) Any of 720 channels with 25-kHz spacing may be selected on frequencies of 118.000 to 135.975 MHz. Pressing the COMM TEST button disables receiver squelch circuits allowing an increase in background noise, thus indicating whether the receiver is operating properly.
5C8
Jun 20/85 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 23-21-01 Page 3
3. Transceiver (Fig. 2)
A. The transceiver is composed of a combination transmitter and receiver which share certain circuits. Frequency selection is available in the 118.00- to 135.975-MHz range with 25-kHz spacing. The transceiver is composed throughout of solid state circuits. Transient protection and voltage regulation circuits ensure correct operating voltages to all circuits.
B. The receiver is normally on unless a push-to-talk circuit is completed. Received amplitude modulated signals are completed through a de-energized antenna relay, to the RF amplifier. The signals are amplified, mixed and converted as necessary, then passed through the detector, squelch and amplifier circuits. Audio output of the receiver is fed to the audio selecting system through the VHF control panel volume control. Selcal signals received are sent to the selcal system on separate circuits (Ref 23-28-0).
C. The same selected frequency is used for both transmitting and receiving. Pressing the push-to-talk button energizes an antenna relay which switches the antenna to the transmitter circuits. The transmitter is amplitude modulated by audio signals from the flight interphone system after crystal oscillator frequencies are mixed and multiplied as required to obtain the final output radio frequency. Transmitted audio is passed through the receiver and sent back to the transceiver sidetone output circuits where it is then connected to output circuits to the VHF control panel volume control and then to the audio selector panels. A minimum power output of 25-watt RF energy may be applied to the VHF antenna.
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