User Manual

3,902,007
3
These features and advantages of the present inven
tion as well as others will be more fully understood
when the following description is read in light of the ac~
companying drawings, in which:
FIG. 1 is a typical waveform of the horizontal scan
lines wherein bursts of an audio signal are transmitted
during each horizontal scan line in a branched TV sys
tem;
FIG. 2 is a block diagram of circuitry for transmitting
an audio signal according to the present invention;
FIG. 3 represents a series of waveforms illustrating
the operation of the circuitry shown in FIG. 1;
FIG. 4 is a block diagram of a receiver embodying the
features of the present invention for recovery of an
audio signal transmitted according to the transmitter of
FIG. 2',
FIG. 5 represents a series of waveforms illustrating
the operation of the circuitry shown in FIG. 4; and
FIG. 6 is a block diagram of a second form of re
ceiver circuitry according to the present invention.
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
FIG. 1 illustrates, typically, horizontal scan lines from
two video pictures in a TV branching system. Each hor
izontal scan line according to standard U.S. practice
has a duration of 63.5 microseconds during which a
horizontal sync pulse is followed by a color reference
burst which is, in turn, followed by a video signal of one
horizontal scan line for one of the branched TV pic
tures. Between the video signal for each picture and the
color reference burst, a blanked interval is located dur
ing which a burst of an audio signal is transmitted using
the subcarrier conventionally used to transmit the
video color signal. As clearly apparent from FIG. 1, a
series of horizontal scan lines are provided wherein al
ternate scan lines are selected to provide one of the
video signals along with bursts of audio signal. Since
the blanking out of a portion of the video signal during
each horizontal scan line necessarily involves a reduced
portion of the video signal, there occurs as a result a
blanked or dark band upon the display tube when ei
ther of the video signals are displayed. As indicated
previously, this blanked portion occupies approxi
mately 10% of the picture area. The present invention
seeks to overcome the blanking out of a portion from
each of the branched video pictures by eliminating the
blanking interval from one of such pictures and reposi
tioning the audio bursts occurring during the horizontal
scan lines thereof to a blanked interval of the other pic
ture where they are arranged as a train of time-divided
audio bursts.
In FIG. 2, a transmitter is shown incorporating TV
cameras for transmitting video signals using the line
sharing principle such as disclosed in the aforesaid US.
Pat. No. 3,725,571. In this regard, as shown in FIG. 2,
there is provided a ?rst camera Cl and a second cam
era C2 for respectively scanning a separate scene.
These cameras comprise state-of-the-art monochrome
or color TV cameras which are operated according to
US. standards wherein two ?elds are interlaced to pro
vide a complete frame of video information. The video
outputs from cameras Cl and C2 are respectively ap
plied to gates G1 an G2. These gates are operated in re
sponse to gating signals supplied by a bistable circuit
BC. A sync generator SG supplies horizontal sync
pulses to the bistable circuit BC which causes this cir
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cuit to provide control signals that alternately render
conductive gates G1 and G2. A reset logic circuit is
provided to reset the bistable circuit at the beginning
of each frame of video information. That is, the bistable
circuit is reset after two ?elds of scanning are com
pleted which would contain 525 lines according to
standard U.S. practice. The gate G1 is rendered con
ductive, for example, during the odd lines of each ?eld;
that is, during lines 1, 3 . . . 525, so that these lines from
camera C1 are transmitted through the gate to an add
circuit 10. The gate G2 is rendered conductive during
time intervals when even numbered lines of each ?eld
are supplied from the camera C2. Thus, lines 2, 4 . . .
524 will be translated through the gate to the add cir
cuit 10. The output from the add circuit 10 is the sum
of the signals delivered through the gates G1 and G2 by
the cameras C1 and C2 as indicated and are delivered
to an encoder 11 wherein they are processed and mod
ulated onto a subcarrier prior to modulation onto a ra
dio-frequency carrier for transmission by well-known
techniques.
The TV system according to the present invention
provides for the transmission and reception of an audio
signal in addition to and apart from the audio channel
provided by the FM frequency channel. A single audio
signal is transmitted by line 19 and has a waveform a
typically illustrated in FIG. 3.
As point for reference hereinafter, the audio wave
form a shown in FIG. 3 has a reference point R. This
audio signal is branched into lines 20 and 21 with line
20 being connected to a delay line 22 which provides
the delay for the audio signal corresponding to approxi
mately one horizontal scan line time period or 63.5 mi
croseconds. The delayed audio signal is shown by the
waveform d in FIG. 3 wherein it will be observed that
the point reference previously referred to in regard to
waveform a now appears 63.5 microseconds later at R’.
The delayed audio signal according to waveform d in
FIG. 3 is delivered to sampler S2 while the branched
audio signal in line 21 is delivered to sampler S1. If de
sired, an audio switch AS may be actuated to deliver an
independent audio signal in line 18 to the sampler S2.
The sampler S2 is rendered conductive in response to
a series of pulses having a repetitive rate shown by the
waveform b in FIG. 3. These pulses occur at approxi
mately 127 microseconds apart; that is, every two hori
zontal scan lines or 2 X 63.5 microseconds. These
pulses are provided by the output signal from a divide
by two circuit 23 which receives input pulses from the
horizontal sync pulse from the sync generator SG. The
divide by two circuit 23 also receives a reset pulse from
the reset logic to reset the divide by two circuit follow
ing the scanning of each frame in the TV picture. The
signal pulse from the divide by two circuit is delivered
by line 24 to the sampler S1 and to a delay monostable
multivibrator 25 which provides a slightly delayed
pulse (e.g., 2.0 microsecond or 3.0 microsecond) to a
monostable multivibrator 26. The multivibrator 26 pro
duces pulses at 127 microseconds apart (waveform e in
FIG. 3) to render the sampler S2 conductive to provide
audio burst A2 of the delayed audio signal, or the inde
pendent audio signal in line 18, as shown by waveform
f in FIG. 3. The burst A1 of audio signal from sampler
S1 and the burst A2 of the audio signal from sampler
S2 are combined by an add circuit 27 whereby a train
of time divided bursts Al, A2 are then followed 127
microseconds later by a second train time divided