Tuned signal detector for use with a radio frequency receiver

Tuned signal detector for use with a radio frequency receiver
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United States Patent [19]
Patent Number:
Douglass et al.
Date of Patent:
Apr. 23, 1996
6/1994 Raiser et a1. ............................ .. 380/20
[75] Inventors: Ralph G. Douglass, Bensalem, Pa;
European Pat. Off. ..... .. H04N l7/00
Arthur R. Furman, Tinton Falls, NJ.
Primary Examiner-James J. Groody
[73] Assignee: Information Resources, Inc., Chicago,
[21] Appl. No.: 350,818
[22] Filed:
Disclosed is a tuned channel detector which includes a cable
path between a radio frequency source and a receiver such
as a TV, wherein the radio frequency source passes ?rst
Dec. 7, 1994
Related U.S. Application Data
Assistant Examiner—JeiTrey S. Murrell
Attorney, Agent, or Firm-—Fitch, Even, Tabin & Flannery
Division of Ser. No. 98,223, Jul. 27, 1993, Pat. No. 5,404,
through an attenuator and second through a signal selection
module comprising two opposing directional couplers and a
single»pole/double-throw switch. The channel to which the
TV is tuned is determined by measuring the TVs local
oscillator signal from the cable which feeds the radio
frequency signal to the TV and, additionally or alternatively,
Int. Cl.6 ................................................... .. H04N 17/00
U.S. Cl.
348/605; 348/607; 455/214
by comparing the signal strength of the input and re?ected
Field of Search ............................. .. 380/20; 455/214,
TV carrier signals at and around the channels under test.
455/226.4, 208, 296, 303; 348/731, 177,
194, 725, 71, 607, 192, 605, 737; H04N l7/00
Signal detection is further enhanced by modulating the
.. 348/731; 348/177; 348/194;
References Cited
2/1978 Jules ................................... .. 455/226.4
12/1982 French et a1.
..... .. 343/194
.. .... ... ..
4,700,222 10/1987 Large et a1.
signal mixed with the local oscillator with a tone and/or
testing only during certain intervals such as the vertical
. . . . . ..
synchronization interval or the power line cycle. A tone
detector having a synchronous recti?er is used to detect low
level local oscillator signals. Tuned channel detection is
further enhanced through the use of arti?cial intelligence
11/1992 Kajita et a1. ............................ .. 380/20
9 Claims, 9 Drawing Sheets
VERT. /-~/ 254
US. Patent
Apr. 23, 1996
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N 922
Notwithstanding the methods and apparatus described
thus far, tuned channel detection through the determination
of a TV receiver's local oscillator signal frequency remains
problematic. The tuners used by the various manufacturers
This is a continuation of application Ser. No. 08/098,223,
?led Jul. 27, 1993, now US. Pat. No. 5,404,161 issued Apr.
of TVs, video cassette recorders (VCRs) and cable converter
boxes (set top converters) naturally have varying character
5, 1995.
The present invention relates to tuned channel detection
systems and, more particularly, to television signal detection
methods and apparatus for determining the channel to which
istics thus making the positioning of an antenna appropri
ately in the vicinity of the tuner problematic. Moreover, the
frequency of the local oscillator signals generated within
TVs, VCRs, and set top converters will range, depending
upon the tuned channel, from about 100 MHz to 1400 MHz
which in and of itself makes detection a considerable task.
In any case, the local oscillator signal’s location will only be
known approximately, and typically it will be a very low
level signal buried down in the noise. It may also be di?icult
to discern local oscillator from the color carrier when they
are in close proximity. These factors along with signal
a television receiver is tuned.
For marketing research, program ratings, consumer sur
veys, and the like, it is often advantageous to determine the
channels to which the televisions within a given viewing
area are tuned. The motivation and desire for collecting such
interference from other sources make it desirable to provide
information is well-known and thus, further elaboration is
a tuned channel detection means having greater integrity
20 than that provided by today’s systems. To this end, better
Conventional methods for determining the channel to
non-invasive methods for detecting and/or verifying the
tuned channel including improved methods of detecting
which a television (TV) receiver is tuned involve the detec—
tion of the TV’s local oscillator signal. The detection of the
local oscillator signal in and of itself is old and well-known
in the art. The prior art illustrates various apparatus, both
invasive and non-invasive to the television receiver cir
cuitry, which have been used as attempts to provide channel
local oscillator signals are desirable.
Given the di?iculties surrounding the initial detection of
local oscillator emanating from a TV and then the di?iculty
detection means which are more robust and less susceptible
to a false reading. Enhanced methods are also used in the
in discerning that signal from other signals and background
detection of the TV’s local oscillator signal. Non-invasive
noise, the present invention focuses upon ensuring that the
process of tuned channel detection has su?icient integrity by
providing not only enhanced methods for detecting the local
methods have typically used an antenna tuned to the TV’s
local oscillator signal, thus no direct physical connection is
made to the television. Invasive techniques, on the other
oscillator signal, but also completely independent means for
hand, typically use a probe to a circuit point within a TV’s
detecting the channel to which the receiver is tuned. The
tuner circuitry or within a set top cable converter box which
35 enhanced techniques used by the present invention for local
provides the detector apparatus with a direct connection to
oscillator detection include: (1) mixing the signal tuned by
the tuner, thus allowing for both the injection and measure
the local oscillator detection tuner with a frequency modu
ment of signals at the tuner or set top converter. While a
lated (FM) signal of the mixer wherein the modulated signal
direct connection makes it easier to detect the local oscillator
is that of a tone which may be PM detected and ?ltered to
detect and measure the presence of the TV’s local oscillator
signal, it is obviously more desirable to use more non
invasive approaches.
Some examples of non-invasive methods for improving
signal in the presence of high levels of noise; (2) sampling
for the measurement of the local oscillator signal only
the integrity of local oscillator signal detection include such
during the vertical synchronization interval (vertical blank
systems as those disclosed in US. Pat. No. 4,723,302 issued
Feb. 2, 1988 to Fulmer, et al.; US. Pat. No. 3,312,900 issued
ing period) during which there is no color carrier present,
thus alleviating di?iculties associated with discerning the
Apr. 4, 1967 to Ja?e; and US. Pat. No. 4,577,220 to Laxton,
local oscillator from color carrier signals; (3) pulse timing of
et al.
the vertical synchronization interval information for
Fulmer, et al. describe detecting the local oscillator signal
of the TV and storing characteristic values of the signal for
the fundamental and a plurality of harmonic frequencies of
the local oscillator signals which correspond to predeter
mined channels. The local oscillator signal fundamental
frequency and the corresponding harmonic frequencies
scrambled channels at a central control computer and con
which are observed are compared to the stored values to
identify the tuned channel. The Fulmer system uses an 55
antenna tuned to the local oscillator or, in the alternative, a
direct connection to the radio frequency (RF) input cable
signal path.
The Jaife and Laxton systems both use an antenna tuned
to the local oscillator signal and placed in the vicinity of the
veying such timing information to the remote channel detec
tors for vertical synchronization interval sampling; and (4)
detecting a 60 Hz modulated signal and then sampling for
the detection of the local oscillator only at the same point in
the power line 60 Hz modulation cycle, thus alleviating the
difficulties of detecting the local oscillator signal when it has
been modulated by the 60 Hz power line.
Tuned channel detection in accordance with the embodi
ment may also be performed in response to re?ected signals
at the radio frequency input of the TV. The signal tuned by
a TV exhibits low impedance to the tuned signal at the TV
radio frequency input thus resulting in a high return loss
tuner circuitry of the TV set. Since signals from the televi
ratio, whereas signals not tuned by the TV exhibit low return
sion line scanning circuitry tend to modulate the local
loss ratios because a majority of their signal energies are
oscillator signal, the Jaffe system extracts the line scanning
re?ected back from the TV, because of the high impedance
information from the local oscillator signal to identify the
mismatch for non-tuned signals. The differing return loss
tuned channel. The Laxton system uses a closed loop 65 ratios can be used to identify the particular channel to which
arrangement to “lock on” the frequency of the detected local
the TV is tuned. The 'retum loss computation is a highly
oscillator signal.
reliable method in and of itself for determining the channel
to which the TV is tuned. An advantage of using return loss
ratios is that the TV carrier signals being measured are high
and, additionally or alternatively, by comparing the signal
strength of the input and re?ected TV carrier signals at and
around the particular channel under test (return loss ratios).
The ability to detect the local oscillator signal is further
enhanced by modulating the signal mixed with the local
oscillator with a tone and testing only during certain inter
level signals whose frequency is known substantially
exactly. Accordingly, since the return loss computation
method is independent of the local oscillator detection
method, the two methods may be used together resulting in
an extremely robust system for tuned channel detection
wherein the possibility for a false detection is very remote.
A tuned channel detector in accordance with the embodi
ment includes a signal path between a radio frequency input
and a TV, wherein the radio frequency input passes through
a signal selection module comprising two opposing direc
tional couplers and a single-pole/double~throw switch. The
vals such as the vertical synchronization interval or the
power line cycle. It may be further advantageous to conduct
the return loss computation only during particular sampling
intelligence techniques.
radio frequency input may be any radio frequency signal
source, including an antenna, a satellite dish, or a cable input 15
from a cable television (CATV) system. The TV receiver as
contemplated herein includes not only TVs, but also VCRs
and set top converters or with any system having a local
oscillator for tuning the front end of a receiver.
The directional couplers are transmission coupling
intervals as well. The integrity of the tuned channel detec
tion is still further enhanced through the use of arti?cial
devices for passing either the forward or backward
(re?ected) signal in a signal path. As described, an embodi
FIG. 1 is a block diagram of a tuned channel detector
connected to a television;
FIG. 2 is a more detailed block diagram relating to the
controller used with the tuned channel detector;
FIG. 3 is a combined block diagram and schematic
diagram of a portion of the tuned channel detector;
FIG. 4 is a combined block and schematic diagram
illustrating an implementation of the signal mixing, ?ltering
ment of the signal selection module has two opposing
and AM/FM detection receiver;
directional couplers such that both the forward and the
FIGS. 5A, 5B, and 5C represent tabular data illustrating
backward signals are separately passed. The switch is used 25
the effectiveness of the return loss computation;
to select between the forward and backward signals. The
ability to select between forward and backward TV signals
FIGS. 6A and 6B are block diagrams illustrating the
is used both for local oscillator detection and the return loss
scrambled channel sampling aspect of the present invention
computation. For local oscillator detection, the backward
wherein FIG. 6A represents vertical synchronization interval
signal provides a source of local oscillator signals leaking
detection and “time stamp” circuitry within the central
back from the TV onto the input signal path, and forward
control computer; and wherein FIG. 6B represents circuitry
signal selection provides the local oscillator detector with
in a channel detector for the reception and utilization of
the TV carrier signal both for calibration of the detector and
for detection of the vertical synchronization intervals.
Within the return loss computation the signal selection
module provides separate measurement of the incoming
(forward) and the re?ected (backward) signals.
“time stamp” information with a phase lock loop circuit;
FIG. 8 is a schematic diagram of a signal selection module
for use with a set top converter; and
FIG. 9 is a program ?ow chart for table-driven software
Alternative embodiments tailored particularly for use
with set top converters may use alternative forward and
backward signal selection modules because local oscillator
signals generated within such converters are at frequencies
signi?cantly higher than those generated within a TV or
conveyed on the radio frequency signal path. It may also be
advantageous to equip a signal selection module intended
FIG. 7 illustrates a signal selection module for use by a
tuned channel detector with a set top converter;
which uses programmable channel detection table entries for
channel detection data and parameters in accordance with
the present invention.
for use with a set top converter with a block converter
between the module’s crossover network and switch which
FIG. 1 is a block diagram showing a tuned channel
shifts the spectrum to the television band.
detector connected to a TV 102, which represents the user’ s
TV under test. TV 102 is used by the viewer to tune in TV
The channel detector includes a tuner for reception of
forward and backward signals and an intermediate fre 50 signals received from a radio frequency source 108. As
illustrated, radio frequency source 108 is a TV antenna but
quency (IF) ?lter narrows the signals from the tuner to a
other radio frequency sources are contemplated. Such addi
particular frequency range. The resulting signal is then
tional radio frequency sources include satellite dishes and
mixed with a signal from a voltage controlled oscillator
(VCO) and presented to a narrow band-pass ?lter allowing
detection by an amplitude modulation (AM) detector. This
circuitry is used both for the detection of local oscillator and
for the detection of incoming and re?ected TV signals for
the retum loss ratio computation. The output of the VCO
cable TV inputs. Radio frequency source 108 is coupled to
an attenuator 106 by a communication path 116, and the
output of attenuator 106 is coupled to a signal selection
module 104 via a communication path 114. A communica
tion path 110 couples the radio frequency signals from the
signal selection module 104 to the TV 102.
may also be modulated with a tone which is then detected by
a frequency modulation (FM) detector to aid in local oscil 60
The signal selection module 104 comprises two opposing
lator detection. To this end, a tone detector having a syn
directional couplers 120 and 122 and a single-pole/double
chronous recti?er is used to detect low level continuous
throw switch 124. A portion of signals re?ected or radiated
wave (CW) signals (herein the local oscillator signal).
from receiver 102 on communication path 110 are coupled
by directional coupler 120 and presented to a pole “A” of
In the present tuned channel detector, the channel to
which a television receiver is tuned is thus determined by 65 switch 124 via path 126. A portion of input signals from
measuring the receiver’s local oscillator signal from the
signal path which feeds the radio frequency signal to the TV
radio frequency source 108 are coupled by directional
coupler 122 to pole “B” of switch 124 through path 128.
Switch 124 is used to connect either the signal on path 126
or path 128 to a detector tuner 130 of the channel detector
frequencies necessary to produce a 45.75 MHZ intermediate
apparatus via path 112.
within TV102. The particular television local oscillator
frequency needed by the TV 102 to receive each television
frequency signal representation of a tuned channel signal
The detector tuner 130 is a TV tuner which actually
comprises its own local oscillator, a mixer, and an output
channel is substantially the same from receiver to receiver
?lter (not shown). The detector tuner 130 is used to select
and well-known. Since a portion of this local oscillator
signal leaks out onto the input path 110, the local oscillator
signal’s frequency may be detected for the purpose of
portions of television signals on path 112 for analysis by
later circuitry as is described in detail later herein. The
output bandwidth of detector tuner 130 is typically about 6
MHZ from about 41 MHz to 47 MHz. One such tuner is
determining the channel to which the TV 102 is tuned. The
local oscillator leakage signal can be quite small and may be
Phillips model UV936, which covers the spectrum from
buried in a high level of noise and/or TV carrier and
about 50 to about 800 MHz.
sideband signals. The embodiment may be reliably used to
Detector tuner 130 presents selected radio frequency
signals at an intermediate frequency of 44 MHz. The output
detect a television local oscillator signal even when the local
oscillator leakage signal level is well below the noise level.
of detector tuner 130 is further ?ltered by an IF ?lter 132
Moreover, as will be appreciated by those skilled in the art,
which has a bandwidth of approximately 1 MHZ with cutoff
the above may also be used to detect any low level continu
frequencies at about 43.5 and about 44.5 MHz. The pass
ous wave (CW) signal in high noise levels.
band of IF ?lter 132 thus passes the signals selected by
To perform local oscillator detection, the controller 200
detector tuner 130 as an intermediate frequency signal at 44
puts the switch 124 in its “A” position to select backward
20 propagating signals from TV 102. It is advantageous to
The output of IF ?lter 132 is applied to a signal path 135
attenuate the radio frequency source signal delivered to the
and is ampli?ed by an IF ampli?er 133. In one embodiment,
TV 102 to a level no larger than necessary to receive a clear
a Motorola MC 1350 video ampli?er was used as IF
picture so that the local oscillator signal from the TV 102 is
not completely masked. By attenuating the source signal,
ampli?er 133. The resulting signal and the output of a
voltage controlled oscillator (VCO) 134 are then mixed in a
mixer 136. The output signals of mixer 136 are connected to 25 one can ?nd the frequency location of a very low level local
oscillator signal which might otherwise be lost in the source
a very narrow band-pass ?lter 138 (e.g., a 10.7 MHz
bandpass crystal ?lter having a 15 KHz bandwidth), which
signal and its re?ection. Attenuator 106 is provided for this
in turn presents its output to an AM detector 140 and a FM
purpose, and it may be ?xed, switchable or variable via
tone detector 142. While the bandpass ?lter 138 used in the
preferred embodiment is a 10.7 MHz crystal ?lter, other
types of ?lters at other frequencies may also be practical for
use within alternative embodiments. Taken together VCO
control path 107.
The controller 200 implements local oscillator detection
of signals on path 112 by stepping the selection performed
ment as discussed below. Various control paths are used by 40
the controller 200 to control the apparatus. A switch control
by detector tuner 130 from one expected local oscillator
frequency to another until a local oscillator signal is detected
at the output of the detector tuner 130. The controller 200
controls the detector tuner 130 to nominally place an
expected local oscillator frequency at about 44 MHz and the
selected signal is connected to mixer 136 via the ?lter 132
and IF ampli?er 133. Controller 200 then controls VCO to
apply a signal to mixer 136 having a frequency which will
center the expected frequency from detector tuner 130 in the
path 125 allows the controller to change the position of the
switch 124 between its “A” and “B” positions to select
passband of band-pass ?lter 138.
Local oscillator signals, although generally known, can
signals either from the source 108 or the TV 102 for
vary depending upon the particular TV 102 under test. In
order to cover the range of possible signals, the VCO 134 is
134, mixer 136, band-pass ?lter 138, AM detector 140 and
FM tone detector 142 represent an AM and FM ?ne tuning
receiver which is enclosed by a dashed box labeled 260.
A controller 200 is used to control the apparatus. The
controller 200 could be a human operator, but in the present
example is a microprocessor controlled computing arrange
presentation on path 112. A gain control path 212 and a data
control path 214 control the detector tuner 130 to select the
particular frequency bands from the signals on path 112 and
presented by controller 200 with a sweep voltage at its input
which causes a sweep of frequencies from the VCO 134 to
allow for some deviation of the local oscillator signals from
regulate the amplitude of the selected signals. A control path
216 controls the gain of the IF ampli?er 133, and a signal on
control path 251 controls the output of VCO 134. The
controller 200 also receives input signals from an AM detect
signal path 141 and a FM detect signal path 143 which are
their nominal 44 MHz while still providing for accurate
detection within the swept frequency range. Frequency
sweeping also allows for fairly wide tolerances in the design
of the mixer 136. Since the expected local oscillator signal
is received at approximately 44 MHZ, the frequencies from
used as described below.
the VCO 134 necessary to drive a 10.7 MHz output at mixer
It should be appreciated that the apparatus described
herein selects from the input radio frequency signal path
which feeds radio frequency signals to the TV 102 thus
providing access to various input radio frequency signals as
well as re?ected and leaked signals propagating backwards
from the TV 102 along the input signal path. The apparatus
136 comprise a frequency sweep in the vicinity of 33.3
There are ?ve (5) possible modes of local oscillator
testing which may be used by the tuned channel detector
apparatus. The modes of local oscillator testing, in order of
of FIG. 1 is used to detect and measure incoming and 60 increasing testing time, are: (l) amplitude testing; (2) tone
re?ected TV picture carrier signals and to detect and mea
testing; (3) sampling testing; (4) line synchronization sam
sure the local oscillator signals leaking out from the TV 102.
pling; and (5) scrambled channel sampling. Advantageously,
Such detected and measured signals are used to identify
the testing modes may be used individually or in combina
which of a plurality of television channels the TV 102 is
When using amplitude testing to detect local oscillator,
the controller 200 tunes detector tuner 130 to the proper
The TV 102 includes a local oscillator (not shown) which
generates a signal having a selected one of a plurality of
frequency, provides the appropriate VCO 134 output signals,
and searches a narrow spectrum at the output of band-pass
?lter 138 for a signal at the appropriate local oscillator
frequency. The AM detector 140 is used to detect a signal
which matches the expected local oscillator signal to within
interval detector 254 to determine the vertical synchroniza
tion interval rate and then software is used to generate a
“pseudo-sync” for use during the sampling mode. Video is
turned off (switch 124 position changed to “B”) after
“pseudo-sync” is established.
some predetermined tolerance of amplitude and frequency.
Tone test is used if the amplitude of the local oscillator is
so low that it cannot be reliably differentiated from the
re?ected “noise” by the AM detector 140. Tone detection is
Occasionally the local oscillator of a TV 102 will be
modulated by the 60 Hz power line signal to such an extent
that the local oscillator will “sweep” through a narrow band
performed by FM modulating the signal generated at VCO
of frequency and thus a steady level cannot be maintained
134 prior to mixing that signal with the incoming signal 10 for measurement. The presence of the 60 Hz modulation of
from detector tuner 130 at mixer 136. Using a combination
a local oscillator signal may be detected by the controller
of audio ?lters and a synchronous tone detector, a local
200 from signals on path 141 at the output port of AM
oscillator signal can be reliably detected even in the pres
detector 140. Once detected, the 60 Hz synchronization
ence of signi?cant noise. This is so because an FM signal,
sampling method may be used by determining the 60 Hz
when mixed with noise, will produce more noise. However,
synchronization from a 60 Hz synchronization detector 258
the presence of a continuous wave local oscillator signal
connected to a 60 Hz power source 256. 60 Hz sampling can
even buried deep below the noise level, will result in a tone
be used to sample the modulated local oscillator signal at the
which, with proper ?ltering, can be detected. Controller 200
same location in its “sweep,” and then integrate the results
generates the tone used for the FM modulation by varying
similarly as previously described for vertical synchroniza
the VCO 134 control signal on conductor 251. When the FM 20 tion interval sampling using sample-and-hold and signal
modulated signal from VCO 134 is mixed at mixer 136 with
integration techniques.
an incoming expected local oscillator signal, an FM modu
The 60 Hz and vertical synchronization interval signals
lated 10.7 MHz signal will result. The PM tone detector 142
“sampling” test methods) are used for performing
is used to detect the tone in the 10.7 MHz signal.
sampled tuned channel detection methods only during the 60
The sampling test may be used with either the amplitude 25 Hz and vertical synchronization interval sample periods.
or tone modes of testing. Sampling is used because the local
When no local oscillator signal is detected at an expected
oscillator signal required to tune the majority of TV channel
frequency, the controller 200 re-tunes the detector tuner 130
signals lies in the vicinity of the color carrier signal of the
to select a new expected local oscillator signal and the above
channel which lies seven (7) channels above the channel in
tests are again performed.
question. Of course, when no TV channel exists seven 30
The present embodiment may also be used to detect a
channels above the channel in question, then interference is
channel by determining the return loss in re?ected
not an issue. In theory, the color carrier of the interfering
signals. Since a receiver exhibits matched imped
channel will be 170 KHz away from the expected local
signal while exhibiting mismatched imped
oscillator signal of the channel in question. However, while
amplitude detection should be adequate if the local oscillator 35 ance to signals not tuned at the radio frequency input, the
result is high return loss for tuned signals and low return loss
signal level is larger than the re?ected color carrier, due to
for non-tuned signals, because a majority of their energies
real world tolerances the local oscillator could be confused
are re?ected back from the receiver due to the high imped
with the color carrier or its sidebands if the local oscillator
ance mismatch for non-tuned signals. Differing return loss
signal level is smaller than the color carrier. In order to avoid
are thus used to identify the particular channel to
possible confusion between an expected local oscillator
signal and a possibly interfering color carrier signal, the
expected local oscillator signal can be sampled during the
vertical retrace interval of the possibly interfering channel
(vertical blanking) when the color carrier is not present.
Thus, if one looks for local oscillator only during the vertical
retrace interval of the interfering channel, typically seven
channels above the channel in question, then the local
oscillator signal of the channel in question cannot be con
fused with the color carrier of the interfering channel. The
vertical synchronization or retrace interval is only about 1.2
milliseconds, thus it takes successive samples using a
identify the tuned channel of a receiver. Prior to performing
tuned channel detection using the return loss method, a
pro?le of the return loss characteristics of a receiver is
created and stored in controller 200. At its very simplest, the
return loss pro?le would consist of a value representing the
ods of testing discussed thus far, but vertical synchronization
path 135 to composite video which is then presented to
vertical synchronization interval detector 254 which pro
vides vertical synchronization interval information to con
troller 200. The controller 200 uses vertical synchronization
reflected picture carrier signal strength measurement for
each possible tuned channel. (Other components of the
television signal might also be used.)
The tuned channel detection method then successively
tunes detector tuner 130 to select the picture carrier of
possible tuned channels and compares the measured
sample-and-hold technique and signal integration to get a
reliable reading. Hence, it takes longer to get a reading with
vertical synchronization interval sample than with the meth
interval testing is no less reliable.
With the switch in position “B” and the detector tuner 130
tuned to the interfering channel (where the local oscillator of
the channel in question would lie), the proper vertical
synchronization interval can be extracted to determine the
correct sampling interval corresponding to the vertical syn
chronization interval. A video detector 252 is provided to
convert the non-baseband output of IF ?lter 132 via signal
which the TV 102 is tuned, as will now be described.
The expected return loss of each tuned channel can be
used in a return loss tuned channel detection method to
re?ected picture carrier signal strength value with the stored
pro?le. When the measured value matches a value stored in
the pro?le of controller 200, a likely tuned channel has been
More complex expected signal pro?les, as discussed
below, may be produced and stored to improve the certainty
of channel detection. Further, such pro?les may be stored in
controller 200 during manufacture or the pro?le may be
learned by the tuned channel detector during setup opera
tions when the channel detector apparatus is ?rst connected
to TV 102. In the latter “learning” case, an operator or
automated equipment would tune the TV 102 to successive
channels and allow the detector apparatus to measure and
store the necessary values at each tuned channel to create the
to ensure fairly constant picture canier measurements
because no picture level information is present during ver
tical retrace.
To prepare a pro?le, attributes are determined for the
FIG. 2 illustrates controller 200 which includes a micro
measured diiferences between the forward and backward
signal strengths for one or more picture carrier signals at and
processor 202. Microprocessor (uP) 202 is connected to the
basic apparatus of the tuned channel detector for controlling
various portions thereof. The SIGNETICS 80C552 micro
adjacent to the channel being tested. The controller 200
accomplishes this by placing switch 124 in position “A” for
backward signal selection and position “B” for forward
signal selection. By comparing the forward signals with the
controller has been used in the preferred embodiment as
backward signals, a coe?icient which can be stored as an 10
“attribute” for the particular signal is computed for later
channel identi?cation. Once attributes are determined for a
particular channel, the TV 102 channel is changed to the
next channel and the controller 200, having been noti?ed
that the next channel is tuned, then determines the attributes
for the next channel as described. Once stepping through all
channels and once the controller 200 has attributes for all
channels, then the controller 200 compiles a TV pro?le from
the channel attributes. FIGS. 5A, 5B, and 5C represent
values accumulated in preparing such a pro?le.
In FIGS. 5A, 5B and 5C, the data illustrated in tabular
The microprocessor 202 is connected to an optional
terminal 218 which may be used for manual operation of the
detector at a remote location primarily for testing the appa
ratus and for controlling manual learning. Optionally, con
troller 200 may include an LED numeric display 220 which
provides an indication representing the channel to which the
TV 102 is tuned, and various colored lamps 222 which
form was obtained with a tuned channel detector by mea
suring the difference between the incoming picture carriers
and their re?ection (in db) from the TV 102 receiver (herein
Sylvania Model #19C 518). The TV 102 was tuned to
channel 25 through channel 35, and then the signal re?ec
microprocessor 202. A detailed description of the instruction
set, interfacing requirements, etc., can be found in the
SIGNETICS (Phillips) Data Book “80C51-based 8-bit
microcontrollers.“ The microprocessor 202 is, of course,
associated with read only memory (ROM) and random
access memory (RAM) components and appropriate inter
face circuitry (not shown), all of which may be incorporated
within microprocessor 202.
indicate apparatus’ mode and operating conditions.
A data path 204 connects microprocessor 202 with a
central control computer 206. Generally, the public tele
phone network and modems are used for data path 204
between microprocessor 202 and central control computer
tions were measured for the tuned channel and the two
adjacent upper and lower channels. This data would be
“learned” by the system and would become the “attributes”
206. Industry standard RS-232 communication protocols
of the TV 102 under test. The data collected are shown in 30 and circuitry are provided to interface the microprocessor
part in FIG. 5A.
With the “learned” pro?le generated for all channels, the
controller 200 may test channels sequentially by measuring
the pro?les for all channels being tested by looking for a
match with the pro?les in the “learned” table for all chan
nels; if the pro?les do not match for an individual channel,
then the next channel in sequence is tried. A “?gure of merit”
is determined for differences between learned and measured
values. The channel having the lowest “?gure of merit” is
picked as the tuned channel. Once the measured pro?le
matches the learned pro?le, the tuned signal is detected.
Measuring the detection of one or more adjacent signals
202 to the terminal 218 and data path 204. Dedicated
RS-232 driver/receiver chips are readily available for this
purpose. Input and output (I/O) ports are available on the
microprocessor 202 for sending and receiving data to and
from various portions of the subject channel detector appa
The control voltage presented to VCO 134 via path 251 is
a summation of several voltage sources controlled by micro
procesor 202. “Coarse tune” voltage source 230, “?ne tune”
voltage source 232, “calibrate” voltage source 234 and
“tone” signal voltage source 236 are all summed together at
summing junction 250 which provides the input voltage to
VCO 134. Coarse tune voltage source 230 and ?ne tune
dance with this method. It has been determined that reliable 45 voltage source 232 are controlled at separate outputs of a
will improve the chances of a correct detection in accor
channel detection may be performed using return loss where
digital to analog converter (DAC) 224, output paths 229 and
only one or two adjacent signals are measured in addition to
231 respectively which may be external to and controlled by
the signal under test. This is done, for example, by measur
ing the two lower adjacent signals, the two upper adjacent
the microprocessor 202 or incorporated within microproces
signals and the signal being tested (?ve signals in total).
Note that “adjacent” signal means adjacent in signal fre
sor 202.
Coarse tune voltage source 230 presents a voltage to the
VCO 134, placing the selected signal output from mixer 136
generally in the vicinity of bandpass ?lter 138. Fine tune
quency and not necessarily in channel number. Thus, Chan
nel 13 is adjacent to Channel 23, not 14, as is understood by
voltage source 232 steps in voltage steps at 1/5 that of coarse
those skilled in the art.
tune voltage source 230 and ?ne tune voltage source 232 is
Return loss testing may also be used with either the 60 Hz 55 used under control of microprocessor 202 to provide the
sweep voltage at VCO 134. Calibrate voltage source 234
or vertical synchronization sampling modes. In fact, since a
provides under control of microprocessor 202 a temperature
constant picture canier signal ensures more accurate return
compensating voltage component which is driven via signal
loss ratios, it is desirable to use vertical synchronization
sampling while computing return loss ratios. In this regard,
it should be noted that vertical synchronization sampling is
actually different when done for return loss than when done
for local oscillator testing. In particular, with return loss
testing, the vertical synchronization is derived from the
channel being tested rather than some interfering channel.
Since the channel picture carrier itself, as opposed to the
corresponding local oscillator, is the signal which is being
tested, there is no interfering channel. The sampling is used
path 233 by pulse width modulator (PWM) 226. PWM 226
may also be incorporated within microprocessor 202. The
tone voltage source 236 may be any tone used for frequency
modulating the output of the VCO 134. A control path 237
is also provided to tone detector 238 and microprocessor 202
to facilitate tone detection.
The AM detected output from the ?ne tuning receiver 260
on path 141 is received by controller 200 and ampli?ed by
an ampli?er 240. A sample-and-hold 241 having a micro
processor controlled solid state switch is used to sample the
to provide a 10 KHZ square wave output. The PLL 318 is
implemented with a LM567 tone decoder and used as a
detected signal prior to ampli?cation. The output of ampli
?er 240 is presented at an analog to digital converter (ADC)
phase adjuster. The integrator 320 may be readily imple
228, a level detector 242, and a 60 Hz detector 244. ADC
228 provides digital representations of analog inputs. The
mented with an operation ampli?er, the design of which is
well-known in the art. Similarly, the ?lter/sarnple-and-hold
level detector 242 is typically implemented as a comparator
con?guration implemented by operational ampli?er 314 and
sample-and~hold 315 are also well-known in the art.
The “tone test” is carried out with the above-described
Mz detector 244 is typically implemented as a tone detector
tone detection circuitry as follows. First, the tone voltage
circuit, such as that provided by the LM567 chip, the output 10 source 236 is enabled by microprocessor 202 to provide a 10
circuit and accordingly, sends a signal to microprocessor 202
when a predetermined threshold level has been passed. 60
of which sends a signal to microprocessor 202 indicating the
presence of a 60 Hz tone. The detection of the 60 Hz tone
is used by microprocessor 202 to determine whether to use
the 60 Hz line synchronization sampling mode.
The output signals from FM tone detector 142 on con
ductor 143 are sampled with sample-and-hold 247, then
ampli?ed by an ampli?er 246 and presented to a ?lter 248
(e.g., a continuous wave signal from a TV or VCR), an FM
modulated 10.7 MHZ signal will result when the output of
mixer 136 is converted to that frequency. Using a combi
which is a narrow band-pass ?lter at 10 KHz for use with the
“tone testing” method wherein the tone generated at tone
voltage source 236 is 10 KHZ and the tone detected at tone
detector 238 is also 10 KHz. The output of ?lter 248 is
presented to tone detector 238 via signal path 249. The
output of tone detector 238 is then presented to ADC 228 via
signal path 239. ADC 228 thus provides at least two input
channels, one for the ampli?ed AM detected signal from
ampli?er 240 and one for the output of tone detector 238.
Although shown as a separate circuit, ADC 228 may also be
incorporated within microprocessor 202.
In FIG. 3, the generation of tone voltage source 236
summing junction 250 and the tone detection circuitry are
shown in more detail. The summing junction 250 is imple
mented by an operational ampli?er 302 which receives at its
inverted input the sum of the signals from coarse tune
voltage source 230, ?ne tune voltage source 232, calibrate
voltage source 234 and tone voltage source 236. The output
signals from ampli?er 302 are presented to VCO 134 via
conductor 251.
The signal from tone voltage source 236 is presented to
summing Junction 250 as a triangle waveform, though a
pure sinusoid would also work. To generate the triangle
KHZ tone to summing junction 250. The output of summing
junction 250 is then applied to VCO 134 via path 251. In
response to the signal on path 251, VCO 134 generates an
FM modulated output signal which is mixed in mixer 136
with the signal selected by detector tuner 130. When the
selected signal is mixed with the incoming local oscillator
waveform, a signal from square wave source is presented to 40
a phase lock loop (PLL) 318 and variable resister 319 which
nation of audio ?lters and a synchronous tone detector, a
local oscillator signal can be reliably detected even in the
presence of signi?cant noise, since noise will not produce a
tone and hence will not produce an output from the syn
chronous recti?er.
An FM discriminator or slope detection on the steep
crystal skirt can be used to detect the 10.7 MHZ intermediate
frequency signal. In an alternative embodiment of the tuned
channel detection apparatus, the 10.7 MHZ crystal ?lter
design was eliminated by using a double conversion fre
quency shift keying (FSK) chip where ?ltering could be
done at 455 KHZ using inexpensive ceramic ?lters. In
addition, as should be appreciated by those skilled in the art,
the tone injection method of discerning a low level continu
ous wave signal is not limited to a particular application, and
thus may be useful to detect any low level continuous wave
signal, not just local oscillator signals.
When the synchronous recti?er output of the operational
ampli?er 304 of tone detector 238 is synchronized with the
tone voltage source 236, the ampli?ed and ?ltered signal
appearing at the input to the synchronous recti?er from ?lter
248 is a distorted sine wave plus noise if a local oscillator
act as a phase shifter to adjust the phase of the square wave.
signal to be detected is present. Alternatively, when no local
The output of PLL 318 is presented to integrator 320 which
provides a triangle waveform at its output. The tone detector
238 comprises two parts, namely a synchronous recti?er
operational ampli?er 304 (also known as a “locking ampli
?er”) and a ?lter/sample-and-hold implemented with an
oscillator signal is present, only noise will be presented from
operational ampli?er 314 and sample-and-hold 315 under
microprocessor control. The synchronous recti?er output is
analog to digital converted at ADC 228.
the output of ?lter 248. When the fundamental of the
distorted sine wave signal is in phase with the synchronous
recti?er, the result at signal path 313 will be a full wave
recti?ed signal. This occurs because when the incoming sine
wave goes positive during one-half the cycle, the gain is +1
resulting in a positive going half cycle and during the second
The synchronous recti?er provided at operational ampli
?er 304 has unity gain (+1) when switch 306 is opened and
half cycle the sine wave goes negative but the gain is also —1
resulting in another positive half cycle, hence a full wave
recti?ed output is produced. Note that any noise, even
a gain equal to —1 when switch 306 is closed. The respective
though it may be signi?cantly larger than the continuous
gain from operational ampli?er 304 is provided by making
wave signal, will not result in recti?cation since it is random
resistor 310 and resistor 312 equal to one another and by
making resistor 308 equal to ten times that of resistor 310 or
312. The synchronous recti?cation is controlled at switch
306 by the square wave source 316 via control path 237.
Phase lock loop (PLL) 318 ensures that the recti?cation
in phase and frequency relative to the operation of the
timing is aligned with the triangle wave output of tone
voltage source 236. The PLL 318 is adjusted to produce
maximum in-phase output with the tone signal. More par
260. As illustrated, all functions of the ?ne tuning receiver
260 are implemented by a single FSK receiver chip 401. In
the embodiment of FIG. 4, the FSK receiver chip 401 is a
FIG. 4 shows an embodiment of the ?ne tuning receiver
Motorola MC3356 data receiver which includes a front-end
mixer/local oscillator. Tuning of the VCO 134 frequency is
provided from the voltage at summing junction 250 which is
ticularly, unity gain is provided by the synchronous recti?er
when the triangle wave is positive and —1 gain is provided
when the triangle wave is negative.
synchronous recti?er operation of operational ampli?er 304.
applied to varactor diode 402. The resultant capacitance
changes of varactor diode 402 affect a tank circuit imple
In one embodiment, the square wave source 316 is
mented with capacitor 403, capacitor 405, and inductor 404,
provided by a 500 KHZ square wave source divided by 50
which controls the oscillator output frequency. The 10.7
MHz ?lter is implemented with crystal 406. The resulting
circuitry used by the microprocessor 202 at the remote
detector. A precision 60 Hz clock signal is derived from a
10.7 MHZ bandpass ?lter has a 15 KHz bandwidth. As
implemented, the VCO 134 is provided by varactor 402
crystal oscillator 602 at the head end. Each of the remote
channel detectors generates clock signals which are syn
chronized or “locked” to the central clock signals using a
wherein the local oscillator may be tuned over a narrow
range (approximately 500 KHz). A second varactor (not
shown) may be used for additional temperature calibration.
FM detection as implemented by the MC3356 chip is based
on using slope detection via the steep skirt of the 10.7 MHz
standard phase-lock loop (PLL) circuit 606. The PLL 606
compares a “reference” frequency from a VCO 608 with
synchronizing information from the data path 204 and then
derives a frequency using digital counter 610. The phase
relationship of the two frequencies is analyzed, resulting in
FIG. 5B shows the results of tuning the TV 102 to channel
30 while the re?ections for channels 23 through 37 were
measured. Of course, in actual operation a complete table for
all channels on the system would be generated for use by the
tuned channel apparatus. Then, by looking at each channel
under test starting at channel 25 and comparing the channel
signal plus the two adjacent upper and lower channel signals
with the known “attributes” (FIG. 5A), the controller 200
a correction voltage that tunes the VCO 608 such that the
frequencies at the head end and in the channel detector
“lock” in both frequency and phase. The “reference” can be
broadcast over data path 204 or over a separate data channel
to all remotes. There will, of course, be a transport delay, but
15 this same delay also applies to the TV signals so proper
synchronization is maintained.
At the central control computer 206, composite video
generates an “error” table as illustrated in FIG. 5C.
As an example of such “attributes”, assume channel 25 is
being tested. If channel 25 were the correct channel for
re?ections for the carriers for channels 23, 24, 25, 26 and 27
should be —l0, —l0, —16, —16 and —8 respectively (see FIG.
5A). However in the instant example, the actual measure
ments were —7, —5.5, —4, —6.5 and —8.5 respectively (see
FIG. 5B). The resulting errors: 3, 4.5, 12, 9.5 and —0.5 are
tabulated in FIG. 5C. By comparing the errors, the controller
200 can calculate a “?gure of merit” by summing the
absolute values of all the errors. As illustrated in FIG. 5C,
Fm3 sums the “test” channel plus each adjacent signal (3
values) and FmS uses two adjacent signals (5 values).
Alternative “?gure of merit” computations could be used for
signal is detected with a converter de-scrambler 618. Verti
from one-shot monostable 624 corresponding to each ver
tical synchronization period. The 1.2 millisecond pulse
Fm7 or Fm9 and so on. These are very simple arithmetic
interrupts the central control computer 206 and latches the
current clock count of a counter 612 in a latch 614. The
central control computer 206 periodically tunes to each
scrambled channel, establishes a “time stamp” relative to its
clock (and hence the remote clocks), adds a “correction”
input value to compensate for any communications protocol
delay in order to- maintain constant delays, and ?nally
transmits this information to the microprocessors 202 at the
remotes. Since there will be a slow “drift” input error, an
operations and can be done relatively quickly by the con
updated “time stamp” input should be sent periodically,
troller 200, once tabular data such as illustrated in FIG. 5B
is generated.
cal synchronization interval information is then extracted
from the scrambled signal with synchronization interval
detector 620. A ?ip-?op 622 triggers a 1.2 millisecond pulse
The controller 200 then looks to FIG. 5C and scans the
Fm3 or FmS columns for the lowest ?gure of merit, the
tuned channel is clearly channel 30 which is the correct
typically every ?ve to ten seconds. The update period can be
extended signi?cantly if the central control computer 206
calculates the
rate” for each channel and transmits this
information to the remotes, thus allowing the microproces
sor 202 to compensate for the drift at the remote units.
channel. Note however, that the best returned loss occurs on
At the remote units, as illustrated in FIG. 6B, a closed
channel 31 not channel 30 in FIG. 5B. This is not uncommon 40 loop maintains the phase relationship between the central
and it illustrates that using adjacent signals improves the
control computer 206 and the remote units, wherein PLL
accuracy of the return loss method.
circuit 606 drives VCO 608, which drives counter 610
The return loss method may be used by itself or in
which, in turn, closes the loop to PLL circuit 606. Logic
conjunction with an local oscillator detection method. Each 45 compare 626 conveys phase information to microprocessor
of these methods vary in speed and accuracy depending
upon the particular signal and conditions. Thus, arti?cial
intelligence techniques have been found useful in determin
ing which method to use for particular signals.
local oscillator to be detected lies within the spectrum of an
202 via 8-bit register 628. The VCO 608 output is ANDED
with the logic compare 626 at AND 630, which, in turn,
provides an interrupt signal to the microprocessor 202 and
generates a 1.2 millisecond vertical synchronization interval
pulse at the remote unit, with one~shot monostable 632, thus
providing vertical synchronization interval information for
interfering scrambled channel, the vertical synchronization
the scrambled channel which was decoded at the central
Certain channels are sent in a scrambled mode. When the
computer 206 and which is now in synchronization interval
with the synchronization interval pulses generated for sam
because a common technique for scrambling a channel is to
suppress the synchronization interval information. The syn 55 pling at the remote tuned channel detector units.
chronization interval information could be recovered by
Another approach for conveying the synchronizing infor
interval may not be detected from the scrambled signal
each channel detection arrangement, however, providing
mation with respect to scrambled channels would use a
such will add to the system cost. Circuitry for communica
reference channel (e. g., channel #6), and then have the head
end broadcast reference time shifts (ii) and drift rate
relating the reference channel to the scrambled channel
tion of such information over a cable such as data path 204
provides a less expensive solution, the circuitry extracts the
synchronization interval information at the “head end” via a
de-scrambler converter controlled by the central control
synchronizing information for use at each remote unit from
time to time as required. This reference charmel approach
computer 206. The synchronizing information for scrambled
avoids additional phase lock circuitry.
channels is then conveyed to the individual channel detector
units over the data path 204.
FIG. 6A represents circuitry at the head end associated
with central control computer 206, and FIG. 6B represents
The preceding embodiment involves a tuned channel
detector connected directly to the RF input of a TV 102 and
uses a detector tuner 130 capable of detecting local oscillator
signals generated by a television receiver. When a set top
converter is inserted between the TV 102 and the tuned
channel detector, it is the local oscillator of the set top
converter which must be analyzed to identify a tuned
FIG. 7 shows an alternative signal selection module 700
00 : SKIP this chan.
0l : TEST this chan.
10 : END of seq.; re~start
for use as a substitute for signal selection module 104 when
a set top converter (not shown) is connected to input path
110 before TV 102. Selection module 700 separates the local
oscillator signals from the set top converter, ranging from
00 = NO (Local oscillator
test this chan.)
frequencies selectable by detector tuner 130.
11 : YES (Return loss test
this chan.)
When a set top converter is used, directional coupler 120
may be replaced by a 600 MHz crossover network 702 (a
diplex ?lter), because the TV carrier signals are below 600
MHz while the local oscillator signals leaking back from the
channel #
Channel to be tested
Tuner control #1 to tune to the
picture carrier of the channel
in which the local oscillator
lies in order to pick up the
interfering channel’s vertical
synchroniration interval when in
set top converter are over 600 MHz. The crossover network
sample mode.
exceed 600 MHZ from the communication path 110 to a
block converter 704. The block converter 704 converts the
IF coarse tune
IF ?ne tune
RF gain
IF gain
Tuner control #2 used to tune to
local oscillator signals from the set top converter by a preset
amount down to a frequency which may be received at 25
detector tuner 130. It should be mentioned that block con
verter 704 may be avoided if a detector tuner 130 is used
which is capable of receiving the higher local oscillator
signals from the set top converter.
FIG. 8 is a detailed schematic diagram implementing the
alternative signal selection module shown in FIG. 7 for use
at lst chan.
Return loss test enable
about 668 MHZ to about 1258 MHz, and converts them to
702 passes television carrier signals right to left from
communication path 114 to path 110. The crossover network
702 also passes the leaked local oscillator signals which
Channel enable byte:
the local oscillator for this
IF coarse tune
IF fine tune
rfgain 2
ifgain 2
HIT level
RF gain
IF gain
Initial “hit level” setting
represents a 2 volt threshold
HIT dev
The deviation above the hit
level in which the local
with a tuned channel detector when a set top converter is
oscillator must lie to be a
used by the viewer.
With a table-driven software embodiment, the controller
200 accumulates test instructions and apparatus parameters
on a per channel basis using tables having such information.
The per channel tables represent a segregated database
wherein channel speci?c testing modes are de?ned. The
controller 200 reads each per channel table in sequence;
sample de
Delay between samples
Samples per vertical sync. (or
60 Hz sync.)
Tone test
Determines state of relay A/B
switch during sync. detect
Bypasses the vertical
synchronization interval detect
performs the called-for tuned signal testing; determines
cycle and uses the 60 Hz line
for sync.
whether the current per channel corresponds to the tuned
channel; then reads the next per channel if the tuned channel
has not yet been located. In this way, the controller 200
*denotes parameters which may need to be changed for a particular channel.
The other entries typically are not usually changed.
proceeds through the database of per channel tables until
The above TABLE 1 is intended for use with software
satis?ed that the correct channel has been identi?ed. When
the controller 200 detects that the channel has been changed
at TV 102, then the process is repeated until the new tuned
channel is determined by the controller 200.
As an example of the way in which the parameters
represented by the program ?ow chart shown in FIG. 9
(described below), which implements the table~driven soft
ware scheme using programmable channel detection table
entries for channel detection data and parameters for deter
mining the tuned channel.
The parameters set up the detector con?guration for
contained in the per channel tables are used within the
table-driven software, channel test data associated with the
measurements at the channel associated with the parameters.
detection process are contained in sets of per channel tables
Once the detector is con?gured according to the table
parameters, measurements are then made by the channel
detector for local oscillator signals and/or for TV channel
carrier signals at the various frequencies which are being
considered. In addition, each table entry provides informa
tion speci?c to the channel under consideration. More par
ticularly, information relating to the best method of tuned
channel detection for the particular channel, the “hit level,”
each having an identical format—one for each channel,
corresponding typically to the format shown in TABLE 1
below. The parameters in TABLE 1 are initialized to pre
determined values. Except for the tuner values, initial values
are the same for all channels. The channel numbers start at
entry 02 and go to 108. Within each table are entries which
contain speci?c control parameters for the particular chan
The following TABLE 1 represents a per channel table
entry format for demonstrating the preloading of values used
at each tuned channel detector for controlling table-driven
and “hit deviation” are stored for use by the table-driven
Many of the table parameters are preloaded and usually
do not need to be changed. Some parameters, however, will
need to be adjusted depending upon the local oscillator
frequency, signal level and/or signal-to-noise level. Such
adjustments are facilitated through the training software.
Channel parameter entries having an asterisk(*) denote the
parameters which may require some adjustment. As the
described table entries so the program ?ow chart shown
generally at 900 is able to detect the tuned channel. The
program How starts at the FIRST TABLE 902, at which
program associated with controller 200 proceeds in accor
dance with the table-driven software scheme, the parameters
associated with each channel are used by controller 200 in
point the controller 200 reads the table associated with the
?rst channel to be tested and its associated parameters to
con?gure the tuned channel detector and then proceeds
accordingly. Typically the ?rst channel will be channel 2,
determining how to proceed with its testing.
To look for the local oscillator for the TV 102, the
controller 200 scans through all the channel table entries for
a “match,” displays the channel number on numeric display
however it has been found advantageous to con?gure a
channel table entry 01 chosen as a thermal compensation
220, lights a green light at the lamps 222, and logs the
appropriate channel number either in a data structure asso
ciated with microprocessor 202, or to terminal 218, or to the
central control computer 206 via the data path 204. The
detector continues to monitor the local oscillator signal until
it disappears, at which time the detector turns o? the green
light at the lamps 222 and then seeks out the next tuned
The enable parameter tells the controller 200 whether to
channel for running recalibration routines since there usually
is not a channel 1. The tuner values in the table are not
actually for channel 1 however, rather any channel which is
good for making thermal compensation adjustments will
su?ice (in one embodiment channel 7 was used).
Next ENABLE 902 checks for one of three table entries:
skip, test, or end. End causes the microprocessor 202 to
re-start at FIRST TABLE 902. Skip causes the controller 200
to proceed to NEXT TABLE 906 which increments an index
to the next table. Test causes the microprocessor 202 to
skip the particular channel associated with the table, or
proceed with testing for the channel associated with the
whether to test the channel, or whether the detector has
reached the end of the test sequence and should restart the
present table. SAMPLE 908 determines whether or not a
loop (usually at channel 2). The return loss enable parameter
tells the detector whether to use return loss or local oscillator
testing for charmel detection. By using a program to call up
all of the channel table entries in sequential order, the
controller 200 merely loops through all of the candidate
channels, tests them, and logs them accordingly.
The channel # parameter represents the channel number
(2-108) associated with the particular channel table entry.
The tunerl parameters are used to tune the picture carrier of
the interfering channel in which the local oscillator lies in
con?gures the apparatus for 60 Hz sampling. RL_ENABLE
916 determined whether return loss testing is to be used, and
if not TONE_MODE 918 determines whether tone testing
for local oscillator is to be used.
The actual testing for tuned channel detection is carried
out at RL_TEST 920, TONE_TEST 924, and LO__TEST
928. When a tuned channel is detected with one test, it may
be veri?ed with another test to ensure proper detection.
order to pick up the channel’s vertical synchronization
interval when using the vertical synchronization interval
sampling, or to tune in the picture carrier signals for the
return loss mode of testing. The next parameters relate to the
IF coarse tune, IF ?ne tune, RF gain, and IF gain, associated
with the tunerl con?guration. Then, tnner2 is used to tune the
local oscillator for the particular channel under test. The next
four parameters relate to parameters associated with IF
coarse tune, IF ?ne tune, mixer RF gain, and mixer IF gain
sample mode of testing is to be employed. If a sampling
mode is to be used, SEL_60 910 determines whether 60 Hz
sampling should be used. V-SYNC 912 con?gures the
detector apparatus for vertical synchronization interval sam
pling if 60 Hz sampling is not used, otherwise 60__HZ 914
Channel hits are detected at RL_HIT 922, TONE_“HIT 926,
and LO_HIT 930. As can be seen from the program ?ow
chart 900, once a tuned channel is detected, the channel is
for the tuner-2 con?guration.
repeatedly tested until the channel changes at which time the
next table is selected and the above-described program loop
is then repeated. The described table-driven software
scheme is merely a simpli?ed and basic example of the way
in which tuned channel detection is implemented; numerous
modi?cations and enhancements should be readily apparent
to those skilled in the art.
In particular, an alternative “mixed mode” of tuned chan
particular testing method. The “hit level” parameter repre 45 nel detection has been found useful as an adjunct to regular
sents an initial setting of 2 volts as the threshold for
local oscillator testing. In this mode, selected channels are
The remaining parameters in the charmel table relate to
the criteria for determining the tuned channel and the
determining the presence of the local oscillator signal. The
singled out for return loss testing. All other channels will be
“hit level” may be changed to be more or less than 2 volts.
local oscillator tested. One reason for doing this is that for
The “hit deviation” parameter represents the deviation above
particular channels the local oscillator signal may be too low
the hit level in which the local oscillator signal must lie in
to be detected reliably, or there may be an extraneous signal
that could be confused for an local oscillator signal. In the
mixed mode, selected channels are individually return loss
order to be considered to be a “hit.” The next parameter
determines the delay between sampling when the sample
mode of testing is used, and the parameter after that relates
to the number of samples per vertical synchronization inter
val or 60 Hz sync. The “tone mode” parameter instructs the
tuned channel detector to use the tone method of testing for
tested as scanning occurs. As already discussed, another
the particular channel associated with the table. The “relay”
parameter determines the state of the switch 124 during the
vertical synchronization interval detect cycle associated
with detecting the vertical synchronization interval and the
generation of the “pseudo-sync” referred to above. Finally,
the “elect 60 Hz” bypasses the vertical synchronization
interval detect cycle and uses the 60 Hz line for synchroni
zation during the sampling mode of testing. This may be
done to stabilize the picture carrier signal measurement.
The program ?ow chart of FIG. 9 further illustrates the
table-driven software. The controller 200 uses the above
alternative is to use the various types of testing as checks
against one another to ensure accurate detection. Basically,
the program ?ow illustrated in FIG. 9 is merely a core upon
which higher level programs used by the controller 200 can
build in order to develop more sophisticated testing
In conjunction with the table-driven software and arti?cial
intelligence techniques referred to above, the tuned channel
detector system undergoes a process of “system training.”
Training is de?ned as that process by which the system
“leams” the attributes of the TV 102 operating in a speci?c
environment. This can be done manually for each detector
system or through a process of self-training which uses
arti?cial intelligence programming techniques'in software.
presence of said low level continuous waveform
2. The apparatus of claim 1, wherein said means for
Manual training involves stepping the TV 102 through
each of the active channels. The detector system logs into the
controller 200 all the attributes for each channel. These
attributes will then be used during the “run” mode to identify
which channel is being tuned. The software for this is
frequency shifting comprises means for shifting the input
signal by a sweep of frequencies.
3. The apparatus of claim 1 wherein said second periodic
signal comprises a periodic triangular waveform.
4. The apparatus of claim 1, wherein the detecting means
comprises a synchronous recti?er synchronized with said
second periodic signal; and wherein the apparatus comprises
means for integrating a recti?cation timing signal of said
synchronous recti?er to generate said second periodic sig
relatively straightforward.
Self-training involves arti?cial intelligence techniques
whereby the controller 200 starts with certain assumptions,
then adds to its knowledge through trial and error. The
disadvantage of self-training is that its error rate tends to be
quite high initially and improves with time. The software
must keep track of various trend data. Another type of
self-training that can signi?cantly improve detect time is to
build a “pro?le” of the viewer’s habits. Most viewers have
quite de?nite viewing habits or patterns. Such viewing
patterns can be exploited by testing for the viewer’s most
likely channels ?rst. Some of the attributes stored for each
prises controller means for comparing the signal output from
said synchronous recti?er to a predetermined signal thresh
old to discern the presence of said low level continuous
6. A tuned signal detection apparatus for use with a
television receiver tuned by a local oscillator signal to a
channel would thus include: which channels are active on
the system; the re?ection coe?icient for each signal; the
local oscillator frequency and amplitude for each signal; and
whether local oscillator amplitude, tone, or sampling mode
tuned one of a plurality of incoming television signals
detection is preferable.
One should keep in mind that either the return loss or local
oscillator methods of testing may be used to determine the
demarcated by vertical synchronization intervals; said local
oscillator signal having a different predetermined frequency
for tuning said receiver to different ones of said incoming
. channels to which the TV 102 is tuned, or some combination
television signals, said tuned signal detection apparatus
of the methods may also be used to ensure accurate detec
tion. Unless the local oscillator signal is extremely low or
buried in noise, local oscillator testing is generally faster
than return loss testing, because often the picture carriers
used for return loss measurements have to be sampled only
during the vertical retrace interval, when the carriers are
fairly constant (no picture content). Also, either vertical
synchronization interval sampling or line synchronization
5. The apparatus of claim 4 wherein the apparatus com
means for receiving a signal representing the local oscil
lator signal generated by said receiver;
means for selecting an individual one of said incoming
television signals;
means for detecting the vertical synchronization intervals
for the selected incoming television signal; and
controller means responsive to said detecting means for
sampling may be used with the amplitude or tone local
oscillator methods, and such sampling may also be used with
the return loss method as well. Arti?cial intelligence tech
measuring, only during the vertical synchronization
intervals from the selected incoming television signal,
the local oscillator signal generated by said receiver for
tuning the tuned one of the plurality of incoming
niques may also be used to exploit optimal detection meth
ods based upon particular testing conditions and adversities.
While there has been described the preferred embodi
television signals.
7. The apparatus of claim 6, wherein said selecting means
ments of the present invention, numerous modi?cations and
comprises controller means for identifying an individual one
changes will naturally be apparent to those skilled in the art.
It is therefore intended by the appended claims to de?ne all
such modi?cations and changes as fall within the spirit and
scope of the invention.
What is claimed is:
1. A continuous wave detection apparatus for detecting
the presence of a low level continuous waveform amplitude
within an input signal comprising the low level continuous
waveform and an interfering signal, said apparatus compris
of said incoming television signals interfering with said
8. A tuned signal detection apparatus for use with a
television receiver for tuning to one of a plurality of tele
a source of a ?rst periodic signal;
means for frequency modulating said ?rst periodic signal
with a second periodic signal producing a frequency
modulated signal;
means for frequency shifting the input signal by a fre
quency corresponding to the frequency modulated sig
means for detecting said second periodic signal in the
signal selected by said ?ltering means to identify the
vision signals, the television receiver generating local oscil
lator signals having a diiferent predetermined frequency for
tuning said receiver to each of said plurality of television
signals, the local oscillator signals being modulated by a 60
Hertz power line signal, said tuned signal detection appa
ratus comprising:
means for detecting a synchronized sampling point in 60
Hertz power line modulation cycles; and
controller means responsive to said detecting means for
identifying the presence of one of the local oscillator
signals having a frequency for tuning said receiver to a
particular one of said plurality of television signals,
?ltering means for selecting a signal within a predeter
mined range of frequencies from the frequency shifted
input signal; and
local oscillator signal, and controller means for selecting
said television signal interfering with said local oscillator
only during the synchronized sampling point in 60
Hertz power line modulation cycles.
9. A tuned signal detection system for detecting one of a
plurality of television signals to which a television tuner is
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