User Manual

3,902,007
5
bursts Al and A2. These bursts of audio signal are
added within the encoder 11 to the composite video
signals from add circuit 10 during a blanked guard
band interval provided in the video signals from camera
C2 by a blanker 28 operated in response to the divide
by two signal in line 24. This produces an output signal
from the encoder having the waveform g (FIG. 3)
wherein a given horizontal scan line from camera C1
produces a No. 1 video signal preceded by a color ref
erence burst in the usual fashion and a horizontal sync
pulse. The next horizontal scan line delivered from the
encoder 11 has the form of a horizontal scan line from
camera C2 wherein a video portion is preceded by a
blanked guard-band interval during which audio bursts
Al and A2 are included in the subcarrier for the video
signal. Preceding the guard-band interval is the stan
dard color reference burst and then the horizontal sync
pulse. The signal from the encoder 11 is modulated
with an RF carrier in the usual manner.
It is now apparent that an audio signal can be trans
mitted by audio bursts at a 16 kilohertz rate which pro
vides an approximately 8 kilohertz bandwidth without
transmitting audio bursts during each horizontal scan
line which occur at approximately 16 kilohertz. While
two cameras are shown, each providing a video signal
for transmission using line-sharing principles, an obvi
ous extension is the use of three or more cameras pro
viding separate video signals each of which is transmit
ted using the line-sharing technique outlined with re
spect to the two cameras described above. When three
or more video signals are required, depending upon the
particular need for a TV system, one of the video sig
nals may be blanked to carry bursts of audio signal or,
alternatively, two of the three video signals may con
tain blanking intervals during which audio bursts are
transmitted. In the encoder, ?le bursts of audio signals
may be transmitted onto subcarriers by using the tech
nique outlined in my aforementioned U.S. application
Ser. No. 364,163.
The present invention further provides a method and
apparatus for recovering an audio signal from the audio
bursts transmitted by the apparatus shown in FIG. 2
having the typical waveform g shown in FIG. 3. Two
forms of receiving apparatus are provided which will be
described in connection with the waveform a in FIG. 5
corresponding to that illustrated by waveform g in FIG.
3. In the receiver, according to FIG. 4, the antenna 39
provides a radio-frequency signal to a receiving stage .
40 which delivers a signal to a detector 41. The output
of the detector has the composite waveform a shown in
FIG. 5 and it is delivered to a chroma bandpass ?lter
42 and to a sync separator circuit 43. The signal from
the chroma bandpass ?lter 42 is delivered to a conven
tional video ampli?er (not shown) and further pro
cessed according to techniques belonging to the state
of-the-art particularly, for example, those disclosed in
the aforesaid U.S. Pat. No. 3,725,571. The signal from
the chroma bandpass filter 42 is also applied to a gate
44 which is rendered conductive in response to a signal
in line 45 from a line-sharing logic circuit 46. This cir
cuit receives a controlling input signal from the sync
separator 43. The signal passed through gate 44 is de
livered by a line 47 having branches 47a and 47b con
nected to a gate 48 and a gate 49, respectively. Gate 48
is rendered conductive in response to a signal H1’ in
line 50 and gate 49 is rendered conductive by a signal
H2’ in line 51. The signals H1’ and H2’ are produced
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by an audio gate pulse generator 52. This generator re
ceives a signal from the line-sharing logic circuit 46 as
well as a horizontal sync pulse signal in line 53 from the
sync separator 43. The H1’ signal in line 50 renders
gate 48 conductive by pulses having the time relation
shown by waveform b in FIG. 5 wherein these pulses
occur at approximately 127 microseconds apart. The
H1’ pulses render gate 48 conductive to deliver audio
pulses having the same time relation shown by wave
form 0 in FIG. 5 to add circuit 54. The pulses H2’ in
line 51 occur at 127 microseconds apart as shown by
the waveform d of FIG. 5 but in a slightly timed dis
placed relation with respect to the pulses according to
waveform b in FIG. 5. The H2’ pulses render gate 49
conductive to deliver pulses according to waveform e
in FIG. 5 in line 55 to a delay line 56 which is selected
to have a delay time of approximately one horizontal
scan line or 63.5 microseconds. The audio pulses deliv
ered from the delay line 56 are in the time relation
shown by the waveform f in FIG. 5 and are delivered
by a line 57 to the add circuit 54. The output from this
add circuit is a series of pulses delivered by line 58 hav
ing the time relation shown by waveform g in FIG. 5
where it will be observed that the pulses occur at ap
proximately 63.5 microseconds apart wherein a pulse
from the gate 48 is followed 63.5 microseconds by a de
layed pulse from gate 49 which is, in turn, followed by
an undelayed pulse from gate 48, etc. These pulses are
delivered to a detector 59 whose output is connected
to a low-pass ?lter to provide an audio signal shown by
the waveform h in FIG. 5 which represents recovery of
the originally transmitted audio signal. The output from '
the low-pass ?lter is connected to an audio ampli?er 60
which is, in turn, connected to a speaker 61.
A second form of circuitry is illustrated in FIG. 6 for
the detection of the video signal having the waveform
a in FIG. 5. The circuit illustrated in FIG. 6 makes
greater use of the circuitry necessary to receive the
line-sharing video signals and it makes use of a “PAL”
type of delay line which is included in the line-sharing
receiving circuitry to delay certain of the horizontal
scan. lines in the video signal approximately 63.5 micro
seconds to remove picture lininess. This is accom
plished by a selected line of one of the pictures being
combined with the same line after it is passed through
the ’ delay line such as disclosed in U.S. Pat. No.
3,725,571. This delay line can also be used to obtain
the necessary delay for repositioning the audio bursts
and results in the improvement being obtainable at neg
ligible increase in costs of the receiver. In FIG. 6, the
received signal after passing through a receiving stage
70 is delivered to a detector 71 which provides an out
put in line 72 to a chroma bandpass ?lter 73 and a sync
separator generator 74. The signal from the chroma
bandpass ?lter 73 which has the modulated subcarrier
components of waveform a shown in FIG. 5, is deliv
ered to a gate 75 rendered conductive in response to a
signal in line 76 from a line-sharing gate pulse genera
tor and logic circuit circuitry that receives a controlling
signal from the sync separator generator 74. The signal
from gate 75 is delivered by a line 78 having a ?rst
branch portion 78a connected to a PAL delay line 79
selected to have a delayed time constant equal to ap- '
proximately one horizontal scan line time period or
63.5 microseconds. The output from the delay line is
connected to an add circuit 80. The signal in the
branched line 78b is applied to an ampli?er 81 which