Frequency Synthesizers

The most popiilar form of motor speed control for adjustable-speed pumping is the voltage-controlled pulse-width-modulated (PWM) frequency synthesizer and AC squirrel-cage induction motor combination. The flexibility of apphcation of the PWM motor drive and its 90 percent- - electric efficiency along with the proven ruggedness of the traditional AC induction motor makes this combination popular. 

Each of the three transmitters has two separate frequency synthesizers based on DDS. For the sake of convenience, we henceforth refer to them as DDS(I) and DDS(II). 

TD-NMR and HR-NMR spectrometer systems have a majority of components in common. All spectrometers consist of a magnet, magnet temperature sensors, magnet heater power supply, RF frequency synthesizer, pulse programmer, transmitter/amplifier, sample probe, duplexor, preamplifier, receiver, and ADC, all controlled by a computer. In addition to these items a HR-NMR has several other requirements which include an electromagnetic shim set, a shim power supply, and a second RF locking channel tuned to the resonance frequency of Li. The second RF channel is identical to that of the observed H channel. Figures 10.9 and 10.10 show the basic setup of TD-NMR and HR-NMR spectrometers, respectively. 

There are two ways to collect FLIM data freqnency-domain or time-domain data acqnisition (Alcala et al. 1985 Jameson et al. 1984). Briefly, in freqnency domain FLIM, the fluorescence lifetime is determined by its different phase relative to a freqnency modulated excitation signal nsing a fast Fourier transform algorithm. This method requires a frequency synthesizer phase-locked to the repetition freqnency of the laser to drive an RF power amplifier that modulates the amplification of the detector photomultiplier at the master frequency plus an additional cross-correlation freqnency. In contrast, time-domain FLIM directly measures t using a photon connting PMT and card. 

For quantitative applications the quasi-monochromatic circuit of Fig. 5.2(b) is better. The basic principles of this circuit are similar to those of Fig. 5.2(a), but there are some important differences. The r.f. oscillator and the local oscillator are two frequency synthesizers that are phase-locked to one another to give a difference frequency of precisely defined phase. This difference frequency is very much lower than in the simple heterodyne circuit,... 

A schematic of the automatic network analysis system used for photoelectrochemical cell measurements is shown in Figure 1. The ac signal of 20 mV p/p amplitude is applied with a Hewlett-Packard 3320B frequency synthesizer to the cell and to the reference sig-... 

The basic instrument for performing routine NMRD experiments must contain (1) a variable field magnet (usually an electromagnet) (2) a frequency synthesizer,... 

Tierney et al., 1971] Tierney, J., Rader, C. M., and Gold, B. (1971). A Digital Frequency Synthesizer. IEEE Trans. Audio Electroacoustics, AU-19 48-56. 

Frequency Synthesizer Specialized circuit (usually computer... 

To summarize we have presented here a new concept for measuring optical frequencies, based on a well-stabilized train of optical impulses. This new technique has been applied to the measurement of the hydrogen IS — 2S transition, to calibrate iodine stabilized HeNe lasers, and to the Cesium Di line which is a cornerstone for a new determination of a. This development culminates in the fully phase locked single-laser optical frequency synthesizer. It uses a single femtosecond laser and is nevertheless capable of phase coherently linking the rf domain with a whole octave of optical frequencies. It occupies only 1 square meter on our optical table with considerable potential for further miniaturization. 

Other potential concerns involve the two frequency references used in the experiment - the proton precession frequency forming the basis of the magnetic field determination, and the Loran-C 10 MHz frequency reference used for the NMR and microwave frequency synthesizers. The Loran-C standard is based on hyper-fine transitions in Cs with Wf=0, and so is insensitive to any preferred spatial orientation, and would not introduce a signature for Lorentz violation into the spectroscopic measurements. Bounds on clock comparisons of 199Hg and 133Cs [7,8] place crude limits on the Lorentz violating energy shifts in the precession frequency of a proton of 10-27 GeV, which imply the NMR measurements are free of shifts well below the Hz level. 

In order to verify this result, we measured the frequency gap using a different technique while one ILP laser was locked to the R(56)32-0 aio transition another ILP Nd YAG laser with slightly worse characteristics was first locked to the same transition to subtract frequency shifts due to the use of different iodine cells and then alternately locked to the ai, aio and ai5 component of the P(54)32-0 line. The beat frequency between the two lasers of about 47 GHz was detected by a fast photodetector (New Focus model 1006) and measured by mixing the signal down with a Rb-clock synchronized high-frequency synthesizer. Within the uncertainty of the two measurements, the results of the absolute frequency measurement using the frequency chain were confirmed (see Fig. 4). According to this measurement, the frequency differences between the aio HFS component of the (R56)32-0 line and the ai, aio and ai5 HFS component of the (P54)32-0 line are ... 

He-Ne laser. The frequency of the shifted infrared beam is locked to this reference Fabry-Perot cavity whose length is fixed. By changing the acousto-optic modulation frequency, which is provided by a computer-controlled frequency synthesizer, we can therefore precisely control the dye laser frequency over a range of 250 MHz centered at any desired frequency. 

A major innovation in spectrometer design involved modification of instruments by, in essence, broad-banding the rf source by use of a frequency synthesizer as an input to a broad-band transmitter. (7-11) Nevertheless these instruments remained hybrids in that they only... 

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