Patent US3758881A successfully refreshed from Google Patents.
US3758881A
Expired / Lapsed
US
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Transversal equalizer controlled by pilot tones
Assignee: AT&T Inc
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Filing: 1972-10-13
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Granted: 1973-09-11
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Expires: 1992-10-13
Abstract
Abstract A transversal equalizer is controlled by harmonically related pilot tones transmitted along with the message signals. Two of the tones near the center of the transmission band differ in frequency by an amount equal to the fundamental frequency of the pilot tones. In the equalizer the two special tones are extracted from the center tap of the transversal equalizer and are used to generate amplitude and phase duplicates of the original pilot tones. At the output of the equalizer the distorted original pilot tones are separated from the message signal and subtracted from the duplicate tones, thereby creating an error signal. The control signals for the gains at each tap of the delay line of the transversal equalizer are then developed by cross-correlating the error signal with the tap voltages.
Inventors
- 👤 W Rummler
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 12:44
CPC Classifications
H; H04; H04L; H04L25/00; H04L25/02; H04L25/03; H04L25/03006; H04L25/03012; H04L25/03114; H04L25/03133
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
195 words
Apparatus for equalizing a transmission channel for transmitting a frequency multiplexed signal, the signal comprising message signals and a plurality of harmonically related pilot tones, introduced into one end of said transmission channel, comprising: a transversal filter connected to the other end of said transmission channel, said transversal filter comprising a tapped delay line connected to the transmission channel, a plurality of amplifying means responsive to control signals for separately amplifying the signals appearing at the taps of said delay line, and means for summing the outputs of said plurality of amplifying means to form the transversal filter output signal; means for generating duplicates of the pilot tones introduced into the end of the transmission channel from the signal appearing at one of the taps of said delay line; first filter means for filtering the signals at the pilot tone frequencies from the transversal filter output signal; means for comparing the output of said first filter means with the duplicates of the pilot tones and generating an error signal related to the difference; and means for cross-correlating the error signal with the signal at each tap of the delay line to produce said control signals.
Claim 2
Dependent Claim
195 words
Apparatus for equalizing a transmission channel for transmitting a frequency multiplexed signal, the signal comprising message signals and a plurality of harmonically related pilot tones, introduced into one end of said transmission channel, comprising: a transversal filter connected to the other end of said transmission channel, said transversal filter comprising a tapped delay line connected to the transmission channel, a plurality of amplifying means responsive to control signals for separately amplifying the signals appearing at the taps of said delay line, and means for summing the outputs of said plurality of amplifying means to form the transversal filter output signal; means for generating duplicates of the pilot tones introduced into the end of the transmission channel from the signal appearing at one of the taps of said delay line; first filter means for filtering the signals at the pilot tone frequencies from the transversal filter output signal; means for comparing the output of said first filter means with the duplicates of the pilot tones and generating an error signal related to the difference; and means for cross-correlating the error signal with the signal at each tap of the delay line to produce said control signals.
Claim 3
Dependent Claim
54 words
Apparatus as claimed in claim 1 wherein the plurality of harmonically related pilot tones is distributed throughout the bandwidth of the transmission channel, and at least two special pilot tones have frequencies near the center of the channel bandwidth, said special pilot tones differing in frequency by the fundamental frequency of the pilot tones.
Claim 4
Dependent Claim
99 words
Apparatus as claimed in claim 2 wherein said means for generating duplicates of the pilot tones comprises: a second filter means for filtering the two special pilot tones from the signal appearing at one of the taps of said delay line; means for multiplying the two special pilot tones together; a third filter means for filtering the signals representing the frequency difference of the two special pilot tones from the output of said means for multiplying; and means for generating harmonics of the output signal of said third filter means having the same harmonic relationship as the pilot tones.
Claim 5
Dependent Claim
94 words
Apparatus as claimed in claim 2 wherein said means for cross-correlating comprises: a plurality of multiplying means for multiplying two input signals, the signals at the taps of said delay line being one of the inputs of each of said multiplying means, respectively, and the error voltage being the other input of each of said multiplying means; and a plurality of fourth filter means for filtering the signals representing the frequency difference of the inputs to said multiplying means from the output of said multiplying means, said frequency difference signals being said control signals.
Claim 6
Dependent Claim
26 words
Apparatus as claimed in claim 2 wherein the number of pilot tones is at least one more than the number of taps of said delay line.
Claim 7
Dependent Claim
31 words
Apparatus as claimed in claim 2 wherein said means for generating duplicates of the pilot tones generates the duplicates from the signal appearing at the center tap of said delay line.
Claim 8
Dependent Claim
172 words
A transversal filter connected to one end of a transmission channel and being controlled by pilot tones introduced into the other end of said transmission channel, comprising: a tapped delay line connected to the input of said transversal filter; a plurality of amplifying means, responsive to control signals, for separately amplifying signals appearing at the taps of said delay line; means for summing the outputs of said plurality of amplifying means, the output of said means for summing being connected to the transversal filter output; means for generating duplicates of the pilot tones introduced into said other end of said transmission channel from signals appearing at one of the taps of said tapped delay line; means for comparing the output signal of said transversal filter at each of the frequencies of the pilot tones with the duplicates of the pilot tones and generating an error signal related to the difference; and means for cross-correlating the error signal with the signal at each tap of the delay line to produce the control signals.
Claim 9
Dependent Claim
172 words
A transversal filter connected to one end of a transmission channel and being controlled by pilot tones introduced into the other end of said transmission channel, comprising: a tapped delay line connected to the input of said transversal filter; a plurality of amplifying means, responsive to control signals, for separately amplifying signals appearing at the taps of said delay line; means for summing the outputs of said plurality of amplifying means, the output of said means for summing being connected to the transversal filter output; means for generating duplicates of the pilot tones introduced into said other end of said transmission channel from signals appearing at one of the taps of said tapped delay line; means for comparing the output signal of said transversal filter at each of the frequencies of the pilot tones with the duplicates of the pilot tones and generating an error signal related to the difference; and means for cross-correlating the error signal with the signal at each tap of the delay line to produce the control signals.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-09-10 | 1977-03-12 | 1977-09-11 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-09-10 | 1981-03-12 | 1981-09-11 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-09-10 | 1985-03-12 | 1985-09-11 | $7700.00 | Window Closed / Lapsed |