Downhole transmitter, systems and methods
A transmitter for use in downhole telemetry and/or control is provided. The transmitter includes a mixer; modulator; and signal generation apparatus configured to generate a frequency modulated signal. The mixer is configured to generate an output signal based on the frequency modulated signal. A frequency spectrum of the output signal includes upper and lower sidebands disposed about a suppressed or reduced frequency of the frequency modulated signal. The modulator is operable to modulate an input signal onto the output signal. A telemetry system and associated methods are also provided.
1. A transmitter for use in downhole telemetry and/or control, the transmitter comprising:
a mixer;
a modulator;
a fixed-frequency oscillator, the fixed frequency oscillator being coupled to the mixer; and
a signal generation apparatus configured to generate a frequency modulated signal;
wherein the mixer is configured to generate an output signal based on the frequency modulated signal, wherein the output signal comprises a dual-tone spread spectrum chirp and has a frequency spectrum and the frequency spectrum of the output signal includes an upper sideband and a lower sideband, wherein the upper sideband and the lower sideband are disposed about a suppressed or reduced frequency of the frequency modulated signal;
wherein the mixer is configured to suppress or reduce a frequency component corresponding to the fixed-frequency oscillator from the output signal;
wherein the modulator is operable to modulate an input signal onto the output signal;
wherein the mixer is a double balanced mixer.
2. The transmitter according to claim 1 , wherein the transmitter comprises an acoustic transducer configurable to provide an acoustic signal based on, or derived from, the output signal.
3. The transmitter according to claim 2 , wherein the transducer is adapted to be coupled to a well structure and/or the transducer is operable to propagate a signal via a well structure.
4. The transmitter according to claim 1 , wherein the transmitter comprises an electromagnetic transducer configurable to provide an electromagnetic signal based on, or derived from, the output signal.
5. The transmitter according to claim 1 , wherein the modulator is operable to modulate at least one of:
a signal provided by the signal generator;
a supply or signal provided to the driver;
a supply or signal provided to the fixed-frequency oscillator;
a supply or enabling signal provided to the mixer; and
a supply or signal provided to the transducer.
6. The transmitter according to claim 1 , wherein the signal generation apparatus is configured to provide a sweep signal, such as a glide sweep or stepped sweep, to the mixer.
7. The transmitter according to claim 6 , wherein the sweep signal comprises a linear or exponential up-chirp and/or down-chirp signal.
8. The transmitter according to claim 1 , wherein the signal generation apparatus comprises:
a tuneable oscillator configured to provide a signal to the mixer; and
a signal generator configured to provide a signal to the tuneable oscillator.
9. The transmitter according to claim 8 , wherein the tuneable oscillator is a Voltage Controlled Oscillator.
10. The transmitter according to claim 1 comprising a driver circuit, the driver circuit configured to provide one or more signals based on the output signal to the transducer, and optionally wherein:
an output of the driver comprises a differential signal; and
an output of the driver comprises a pulse-width modulation (PWM) signal.
11. The transmitter according to claim 1 , wherein the modulator is configurable to provide on-off keying and/or amplitude shift keying to the transducer driver and/or to the mixer.
12. The transmitter according to claim 1 , wherein the modulator is configurable to provide phase shift keying and/or binary phase shift keying and/or frequency shift keying to the fixed-frequency oscillator, based on the input signal.
13. A repeater for use in downhole telemetry and/or control comprising the transmitter of claim 1 and a receiver, the repeater being configured to transmit a received signal.
14. A telemetry system for use in wirelessly transmitting data downhole, the system comprising a transmitter according to claim 1 , wherein the transmitter is configured to wirelessly transmit data signals for propagation via a well structure.
15. The telemetry system according to claim 14 comprising at least a portion of the well structure, wherein the well structure is a metallic structure.
16. A method of transmitting data signals in a downhole telemetry and/or control system, the method comprising:
using a mixer to generate an output signal comprising a dual-tone spread spectrum chirp and upper and lower sidebands equally disposed about a suppressed or reduced frequency modulated signal;
modulating an input signal onto the output signal;
using the mixer to suppress or reduce a frequency component corresponding to a fixed-frequency oscillator coupled to the mixer from the output signal; and
wherein the mixer is a double balanced mixer.
17. The method according to claim 16 , further comprising the step of providing the output signal to an acoustic transducer, the acoustic transducer being acoustically coupled to a well structure.