TM
11-5820-922-40-1
SECTION II
DETAILED FUNCTIONAL DESCRIPTION
2-17. With SQUELCH turned on, Rcv Audio
2-12. AMPLIFIER-CONVERTER DETAILED
In from the receiver/exciter is applied
FUNCTIONAL DESCRIPTION.
to voice-operated gain device (VOGAD)
amplifier U2. The VOGAD amplifier cir-
2-13. The following paragraphs detail
cuit maintains a gain-controlled audio
the functions of the amplifier-converter.
output of approximately 100 millivolts
regardless of the audio input. Clipper
circuit CR3 and CR4 removes any high-
filter is used primarily as a low-pass
level transients from the VOGAD audio
output . Amplifier AR1 then boosts the
signals routed between the receiver/
VOGAD audio to a practical operating
exciter and the power amplifier. It
level of approximately 4.5v, peak-to-peak.
blocks rf signals that may be present
during transmit operation. Also, the
2-18. The output of AR1 is applied to
EMI filter receives +28v Battery from
signal detector CR5 and also to enve-
the power amplifier, and routes +28v
lope detector CR2 and CR6. The positive-
Battery (Protected) out to the receiver/
going portion of the VOGAD audio is
exciter. A Tune In Progress signal is
passed by signal detector CR5 and
routed from the power amplifier through
applied directly to the inverting input
the L-C filter network and then to the
of subtracter AR4. The output of CR5
receiver/exciter and the TTY-FSK
represents the signal-plus-noise energy
converter.
at the output of AR1. The signal-plus-
noise energy is routed through signal
compensator Q3 if the signal drops by
audio filter is a low-pass L-C filter
2 db. Therefore, if a signal is weak
network used to filter some of the sig-
and just barely breaks squelch, it can
nals routed between the operator's hand-
degrade by 2 db and still keep squelch
set, receiver/exciter, and the TTY-FSK
broken.
converter and the amplifier-squelch.
Connector J1 will normally have the
2-19. Envelope detector CR2 and CR6
handset connected to it, but will also
rectifies the VOGAD audio and produces
accept the continuous wave (CW) key.
a negative-going audio envelope which is
The following signals are routed through
passed through low-pass filter AR2. The
the low-pass L-C filter network: KY65
output of AR2 is a signal which follows
Keyline, Rcv Audio In, Sidetone Rcv
the audio envelope and, therefore, var-
Audio, AFSK, and PTT.
ies according to the syllabic rate of
the voice energy in the audio signal.
The amplifier-squelch employs circuits
therefore, noise and continuous tone
which are sensitive to the signal charac-
signals are rejected.
teristics of the human voice. The pres-
ence of a voice signal in the Rcv Audio
In will activate circuits which compare
2-20. The syllabic rate signal from low-
the voice signal with a preset signal-to-
pass filter AR2 is routed through SQUELCH
noise ratio. The result of this compari-
SENSITIVITY control R1 to variable gain
son is then used to squelch the received
amplifier AR3. The gain of AR3 is vari-
audio signal. The level, or amount of
able from 3 to 33 as determined by the
voice signal, required to squelch the
setting of R1. The output from AR3 is
audio signal is variable, and is con-
detected by peak detector CR7 and C22
trolled by the SQUELCH SENSITIVITY
and applied to the noninverting input of
control.
subtracter AR4.