Carrier-demodulator

The differential pressure transducer is a model PID-0.1PSID with model CD11 carrier demodulator (Pace Engineering Co., North Hollywood, Calif.). It is operated at 0.4 maximum sensitivity and is connected to a standard potentiometric recorder using the 200-mv. range. The reference side of the transducer is connected to an empty flask submerged in the thermostat (Figure 2). 

He, J., Li, F., Xiao, H. Liu, Y. [2008]. Fiber bragg grating sensor array system based on digital phase generated carrier demodulation and reference compensation method. Proceedings of Optical Fiber Sensors Conference, APOS 2008, Chengdu, China, pp. 1-4. 

To demodulate the signal, it is then necessary to multiply the carrier by itself. Of eourse, the carrier of the driver must be exactly the same as the demodulator one. But, as it is modified to be demodulated, we nevertheless need a common frequency reference for the driver and for the DSP. This reference is delivered by a quartz oscillator. 

The demodulation algorithm is very simple the DSP multiplies the received signal by each carrier, and then filters the result using a FIR filter. This kind of digital filter is phase linear, (constant group delay important for the EC combinations). Other filters may be programmed, other demodulation algorithms may be used. 

Fig. 11.5 Differential phase contrast detection of patterned protein in a 10 mm by 30 mm region, (a) Protein height signal showing ridges of protein in a checker board pattern, (b) Side band demodulated signal image in which the carrier frequency of the ridges is removed to show only the protein envelope. Reprinted from Ref. 21. with permission. 2008 Optical Society of America...

When the return is received, it is demodulated to strip off the carrier frequency. Typically, the return is mixed with , that is multiplied by, cos 2irft and then low-pass filtered to eliminate the high frequency component of the mixed signal. This is the demodulation phase refered to earlier. 

At very high frequencies the luminescence is completely demodulated and only an average intensity is obtained. The maximum frequency of modulation of the response is determined by kr + k f[Parameter]) of the sensor-carrier preparation. 

In many telemetry systems the PCM signal is frequency modulated on to a carrier wave. This is termed frequency shift keying (FSK). In other arrangements, the output of the transducer is converted into fixed step changes of the phase of the modulating signal. A device for this purpose is termed a modulator/demodulator or modem. 

Transducers in the device being tested convert the variable being measured into an electrical signal that subsequently is used to modulate the carrier of an RF transmitter. The signal is received, amplified, and demodulated on the ground, and recorded on magnetic type or on an oscillograph for subsequent analysis... 

Fig. 2.S. Su mmary of some of the shadow masking and surface-treatment results from 3M. A. Photograph of a polymeric aperture mask [30b] used to pattern a wide range of circuits. This mask bears a 6-inch x 6-inch deposition area, with high open aperture ratio. B. Photomicrograph taken of a one-bit RFID circuit patterned using the polymer shadow mask technology [30c], C. Internal clock signal and the externally demodulated rf, or reader signal of the circuit in B (carrier signal was 125...

An additional hypothesis that is consistent with and helps explain the role played by the 16 Hz amplitude modulation is as follows the nonlinear medium demodulates the carrier releasing a 16-Hz signal within the brain tissue, and it is the 16-Hz signal that causes changes in the calcium binding. 

The specific carrier-wave amplitudes (field intensities) which have been found to be effective in producing Ca ion efflux are discussed in terms of tissue properties and relevant mechanisms. The brain tissue is hypothesized to be electrically nonlinear at specific field intensities this nonlinearity demodulates the carrier and releases a 16 Hz signal within ljie tissue. The 16 Hz signal is selectively coupled to the Ca ions by some mechanism, perhaps a dipolar-typ +(Maxwell-Wagner) relaxation, which enhances the efflux of Ca ions. The hypothesis that brain tissue exhibits a slight nonlinearity for certain values of applied RF electric field intensity is not testable by conventional measurements of e because changes... 

Peripherals for user input/output card readers (obsolete), card punches (obsolete), line printers (almost obsolete), laser printers, terminals, also called CRT (cathode-ray tubes), speech recognition devices, speech synthesizers, optical scanners, modems (modulators— demodulators, to piggyback digital data onto an acoustical carrier for telephone transmission), IR laser ports, and so on. 

On the other hand, there are measurements in which signal and noise cannot be directly filtered and the signal has to be transposed onto a carrier wave to be shifted away from the noise frequencies (modulation). Then an amplifier is tuned to the frequency of the carrier wave and the amplified original signal is finally recovered (demodulation). The use of a chopper in optical spectrophotometers is a common example of this process [i]. Ref [i] Horowitz P, Hill W (2001) The art of electronics. Cambridge University Press, Cambridge... 

The use of a phase-sensitive detector to demodulate the f.i.d. signal emerging from the receiver coil is equivalent to providing a rotating frame of reference for the spectrometer itself, as the detector is referenced to the constant carrier r.f. (ft). The f.i.d. signal detected, therefore, contains only phase and intensity information for the difference frequency between the carrier frequency applied and the... 

Fig. 4.1.11 Part of the EFS matrix of Bosch s MM2 rate gyro. Functional parameters are normalized sensitivity S, demodulation carrier phase Ph, resolution Res, self-test signal magnitude B...

For subsequent demodulation and a good signal profile recovery, the period of the ac carrier frequency T = 1/f = 2k/(0 should be small compared to the duration of the signal (i.e., less than 1 s), the ratio being 1 10 in this example. 

Using a fibre network the encoded MMW spectral source signal could be modulated on to the 1.6 / m infrared optical carrier along with all the requisite control and identifier signals and sent to the spectrometer node. That would comprise the absorption cavity, photoelectronic demodulator and circuits with... 

Transformer-coupled isolation amplifiers perform on the basis of inductive transmission of a carrier signal that is amplitude modulated by the biosignal. A synchronous demodulator on the output port reconstructs the signal before it is fed through a Bessel response low-pass filter to an output buffer. A power transformer, generally driven by a 400-900 kHz square wave, supphes isolated power to the amplifier. 

However, for the same data collection time, interferometry is more sensitive to multiplicative noise (i.e., noise proportional to the signal) than continuous-scan interferometry [591]. To eliminate the multiplicative and 1// noise, phase modulation (at 400 Hz) of IR radiation in conjunction with LIA demodulation is used [591]. Since the LIA and some IR detectors need the IR signal to be modulated at a single carrier frequency, a mechanical chopper, phase modulation (when at each position the fixed mirror is dithered at a fixed frequency), or modulation of absorption of the sample is used to produce a carrier frequency. In this case, the TR measurement is referred to as a synchronous multiple-modulation experiment. Multiple modulation is unnecessary if the so-called dc coupled detector which does not require a varying signal is used. 

The signal from a resonant transducer resembles an AM radio signal. It has a carrier wave, at the resonance frequency of the transducer, which is amplitude modulated by the process. The information about the process is in the modulation envelope. An RMS-to-DC (root mean square-to-direct current) converter is used to demodulate the signal. The output of this device is the amplitude of the envelope. 

FIGURE 10.151 Static UPS using a phase-demodulated carrier. (After [2].)... 

Alternatively, a carrier can be inserted into the SSB signal, which can then be demodulated using simple envelope detection. This SSB-FC approach has the advantages of both low bandwidth and low-complexity receiver design, but is inefficient in power use due to the added carrier and usually performs poorly in the presence of noise. 

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