# US 4,395,712 A · Linear detection of a DME signal

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- Number: US 4,395,712 A
- Document ID: US4395712A
- Status: Granted
- Kind: A
- Application number: 06/228,840
- Filed: 1981-01-27
- Granted: 1983-07-26
- Earliest claimed: 1981-01-27
- Assignees: General Signal Corporation
- Inventors: Edward J. O'Hare
- Web page: https://patentgrep.com/patent/US4395712A

## CPC

- G01S 13/788: {Coders or decoders therefor; Special detection circuits}
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES

## Abstract

A DME receiver is arranged to produce, at baseband, a linear replica of an RF input, over relatively wide dynamic range. The DME receiver receives a local oscillator signal from the associated transmitter which is mixed (in a first mixer) with the RF input to produce an IF signal which is a replica of the RF input. The receiver includes an IF amplifier and a bandpass filter serially coupled to the output of the first mixer. Coupled to the output of the bandpass filter is a signal processing circuit with two outputs. The signal processing circuit produces at one output a replica of its input, and at another output a phase shifted and limited replica of its input. Both outputs are coupled to a second mixer. The second mixer has two inputs and an output. By appropriately adjusting the phase of the signal in the signal processing circuit, the phase of that signal (at one input to the second mixer) and of the other signal input to the second mixer are made equal, and as a result, the output of the second mixer is a signal, at baseband, which is a linear replica of the RF input. In one embodiment of the invention, the inputs to the second mixer are at IF and in another embodiment of the invention, the inputs to the second mixer are at a second intermediate frequency, lower than the first intermediate frequency.

## Claims

### Claim 1

A DME receiver, responsive to an RF input signal for generating a linear baseband replica of said RF input for distance determining purposes, including:
a first mixer, coupled to said RF input signal, and to a local oscillator signal,
an IF amplifier and bandpass filter, serially connected to said first mixer,
a second mixer with two inputs and an output, and,
signal processing means with two outputs coupled between said bandpass filter and said second mixer for processing a signal from said bandpass filter to generate a first output signal and a second output signal comprising a hard limited version of said RF input signal, said signal processing means including phase shift means for phase adjusting said second output signal relative to said first output signal, said phase shift means comprising an active circuit element with an input and two outputs, variable reactive circuit means coupled between said two outputs, said two outputs of said active circuit element providing said first and second output signals, respectively,
whereby with the relative phases of said first and second output signals adjusted, said second mixer produces, at baseband, a linear replica of said RF input signal.

### Claim 2 (depends on 1)

The apparatus of claim 1 in which said signal processing means includes
a third mixer coupled between said bandpass filter and said second mixer,
a first input of said third mixer comprising a replica of an output of said bandpass filter and a second input of said third mixer comprising a signal in fixed frequency relation to said local oscillator signal, whereby second mixer has input signals of frequency lower than said intermediate frequency.

### Claim 3 (depends on 1)

The apparatus of claim 1 in which said variable reactive circuit means comprises a variable capacitor.

### Claim 4 (depends on 1)

The apparatus of claim 1 in which said signal processing means comprises
a power splitter with input coupled to said bandpass filter and a first output coupled to said second mixer, and a hard limiter and phase adjusting means serially connected between a second output of said power splitter and a second input of said second mixer.

### Claim 5 (depends on 1)

The apparatus of claim 1 in which said signal processing means comprises
a power splitter with an input coupled to said bandpass filter, amplifying means responsive to one output of said power splitter for supplying an AGC signal, a third mixer with an output and responsive to another output of said power splitter and to another local oscillator signal, fixed in frequency relative to said local oscillator signal, delay means and a video amplifier serially connected to said output of said third mixer, said video amplifier having an AGC input connected to said AGC signal, signal splitter means with an input and two outputs and including said phase shift means connected between said video amplifier and said second mixer, and a hard limiter coupling another output of said signal splitter means and said second mixer.