Directing an antenna to receive digital television signals

Details Directing an antenna to receive digital television signals Directing an antenna to receive digital television signals

1998-12-22

2003-01-21

Miller, John (Department: 2614)

Television

Basic receiver with additional function

For display of additional information

C348S725000, C348S731000, C348S732000, C348S733000, C342S359000, C455S003020, C455S067150, C455S067700, C455S025000, C455S226100, C455S226200

Reexamination Certificate

active

06509934

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to the field of directing antennas, and more particularly, to directing an antenna to receive digital television signals.
BACKGROUND OF THE INVENTION
Conventional Television Signal
FIG. 1
shows a distribution of energy versus frequency for a conventional television (TV) signal
100
, for example, NTSC, PAL, or SECAM. The signal
100
includes three energy peaks, one for video
110
, one for color
120
, and one for sound
130
. As can be seen, conventional television transmitters concentrate most of the energy of the radio frequency (RF) signal in a relatively narrow bandwidth near the frequency of the picture sub-carrier, i.e., ~1 MHz. Therefore, an antenna designed to receive conventional (terrestrial-based analog) TV signals can usually be directed for optimal reception of the video portion by only considering the strength of the signal.
Advanced Television Signal with Interference
FIG. 2
shows a distribution of energy versus frequency for an advanced television (ATV) signal
200
. An advanced television signal can concurrently carry a variety of multimedia content, for example, HDTV, conventional TV, video-text, audio, low-bandwidth TV, etc. In the ATV signal
200
, the energy of the signal, at the transmitter, is distributed substantially uniformly over the entire channel bandwidth, usually 6 MHz. With such a wide spectrum signal, the probability of destructive ghost interference is significantly higher than in the case of conventional TV that has a narrow spectrum signal. As a result, static and dynamic multi-path fading are more likely to corrupt the spectrum of the received ATV signal than in the case of the conventional TV signal. This interference is shown by “notches”
201
-
202
in FIG.
2
.
Multi-Path Fading
Multi-path fading is a result of mostly two effects. The first effect is caused by variations in the index of refraction due to spatial and temporal variations in temperature, pressure, humidity, and turbulence in the atmosphere. These varying atmospheric conditions result in multiple paths from the transmitter to the receiver, each path having a different effective electrical length. The second effect is due to the reflection of the RF signal from different obstacles or objects in the signal path. The second effect produces a more stable multi-path environment when the obstacles or objects are stationary. In either case, the signals arriving at the antenna via different length electrical paths interfere with each other.
It is possible to describe the effect of multipath fading on a passband signal as a superposition of a number of electromagnetic waves. For an ATV terrestrial signal, the highest passband frequency is, for example, 6 MHz. The delay along multiple paths can be in the range of −2 to +25 &mgr;s.
The notches
201
-
202
in the power spectrum will happen when several components of the signal approach the receiver at the same passband frequency but different phases. The depth of a notch can be equal to the full power when the two paths are nearly the same amplitude but opposite phase. In this case, destructive interference results in zero energy at this point in the power spectrum. The ATV receiver cannot process the signal and the receiver effectively becomes inoperative.
Anecdotal evidence has digital television receivers from different manufacturers standing side-by-side in a retail store, each hooked-up to the same antenna, some working perfectly, others totally inoperative. Attempts to “tune” the sets based on built-in signal strength meters frequently are futile or give inconsistent and unpredictable results.
Consequently, in order to determine the optimum direction of a receiving antenna for an ATV receiver, the strength of the received signal alone is not enough to determine the optimal antenna direction. Therefore, it is desired to provide a method and apparatus which can direct an antenna to optimally receive advanced television signals.
SUMMARY Of THE INVENTION
Provided is a method and apparatus for measuring the strength and quality of a digital television signal. The measured values can be used to optimally direct an antenna to an orientation which maximizes the quality of the signal.
Specifically, the invention measures the strength of the signal as a function of the azimuth angle of the antenna. This can be done in the tuner section of a television receiver using an automatic gain control circuit. The flatness of the signal, as a function of the azimuth angle of the antenna, is measured in an adaptive equalizer of the receiver.
These two measured values can be displayed on the screen of the receiver, and the antenna can be adjusted to maximize the flatness of the signal while maintaining the strength of the signal above a minimum threshold. Alternatively, the antenna can be automatically adjusted.


REFERENCES:
patent: 3842420 (1974-10-01), Rabow
patent: 4030099 (1977-06-01), Valenti et al.
patent: 4696053 (1987-09-01), Mastriani et al.
patent: 5053784 (1991-10-01), Hippelainen
patent: 5461305 (1995-10-01), Kim
patent: 5797083 (1998-08-01), Anderson
patent: 5983071 (1999-11-01), Gagnon et al.
patent: 6011511 (2000-01-01), Chuong et al.
patent: 6107958 (2000-08-01), Kelkar et al.
patent: 6201954 (2001-03-01), Soliman

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