Honeywell
COMPONENT MAINTENANCE MANUAL
PART NUMBER 964-0452
I.B.1516A Page 29
Mar 30/01
23-12-01
BFO, which converts the input signal to the correct IF position. As in the receive
section, it is a synchronous modulator that selects the lower or upper sideband
(LSB/USB) as necessary. In this context, it must be borne in mind that the sub-
sequent stages generate the reverse frequency position (Ref. paragraph
4C(4)(c)5).
A volume compressor is effective in the VOICE mode. This function compresses
the volume range of the input signal by 3dB. The subsequent selection stage
suppresses the spectral elements outside the useful bandwidth.
In this concept, suppression of the carrier and the undesired sideband is
achieved by processing the analytical (complex) signal, and therefore, not by
selection measures as in conventional circuits.
3 Functional Description AME Transmission Mode
Selection stage (Ref. paragraph 4C(1)(c)2, 1st paragraph).
Automatic gain control (Ref. paragraph 4C(1)(c)2, 2nd paragraph).
Carrier generation of 25kHz with subsequent BFO, which converts the signal to
the correct IF position. The upper sideband is selected and added to the carrier.
Voice compressor (Ref. paragraph 4C(1)(c)2, 4th paragraph).
The IF signal,
output via D/A converter, D7, with a 100kHz scanning frequency.
4 Functional Description Monitoring Mode
The modulating LF signal (adjusted) appears at the audio output in the VOICE
mode. The level equals the nominal value (when receiving).
Monitoring is not available in the DATA mode. The signal is output via D/A con-
verter, D8, with a scanning rate of 12.5kHz before being amplified in N4-A, and
subsequently filtered in antialiasing filter N4-B, C. It passes via switches S3-C,
A and adjustable amplifier N5-B (Ref. paragraph 4C(1)(b)3) to the audio output.
5 From the 2nd Intermediate Frequency to the Exciter Output
Amplifier, N17, is used for the current-voltage conversion of the D/A converter
output signal. Low-pass filter, L28, suppresses the 3rd harmonic of the 25kHz
IF signal, which would generate spurious aliasing products in mixer, U40, which
represents the conversion stage to the 1st IF of 40.025MHz. The 2 switches,
V71 and V54, prevent the demodulated IF signal from affecting the IF input in
the receive mode. Amplifier, V3, V5 operates with a maximum amplification of
AGC–RF = +2.7V (Ref. paragraph 4C(1)(b)1).
PIN diodes, V43 and V41, are polarized in the forward direction by signals TX
+15V and RX +15V.
Crystal filter, Z40, suppresses spurious signals arising in the D/A converter as a
result of the scanning rate of100kHz.
The subsequent mixer converts the 1st IF signal to the desired RF position by
means of the 1st oscillator (42.025 to 70.0249MHz).
Page 45
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