Precise Phase Control Research Articles

An air-supported polarizer rotator with precise phase control for LF modulation of optical and infrared radiation

A high precision rotator with accurate mechanical phase control has been constructed. The system is primarily designed for the rotation of polarizers, diameters up to 100 mm, to produce amplitude modulation of broad band radiation in acousto-optical instruments for radiation intensity measurement. Rotation speed may be phase-locked at 2, 4 or 8 Hz to a crystal oscillator or over the range 0.625-10.5 Hz to an external signal. Air bearings are used for low friction and noise: acoustic output, at 80 mm, is only 16 mu Pa at 4 and 8 Hz. A high torque motor gives fast rotor acceleration, 57 rad s-2, and broad-band phase control electronics (analogue and digital) utilizing encoding marks on the rotor circumference give good stability over the range of speeds without external adjustment. Outputs at 128 and 4 pulses rev-1 are provided for synchronization of external apparatus such as phase sensitive detectors. The standard deviation, at 4 Hz (240 RPM), in phase determined between pi /2 pulses (4 per rev) is 1 mrad and in frequency, measured over 100 s, is 0.8 mu Hz (2*10-7).

A millimeter wave frequency synthesizer covering the 40?60 GHz waveguide band

This paper describes a millimeter wave frequency synthesizer based on a single broadband backward wave oscillator tube which is capable of covering the entire 40–60 GHz waveguide band with useful power output, low phase noise, and rapid frequency switching. The synthesizer is controlled by an internal microcomputer which sets the reference oscillator frequency through a General Purpose Interface Bus (GPIB) and generates synthesizer coarse tuning corrections through a programmable digital-to-analog converter. The phase/frequency control system uses a frequency discriminator for capture of the source from large frequency errors and a complementary phase lock for precise phase and frequency control.

A Versatile RF Controller

The low level RF system developed for the new Bevatron local injector provides precise control and regulation of the Rf phase and amplitude for three 200 MHz linac cavities. The main features of the system are: ? Extensive use of inexpensive, off-the-shelf components ? Ease of maintenance ? Adaptability to a wide range of operation frequencies. The system utilizes separate function, easily removed RF printed circuit cards interconnected via the edge connectors. Control and monitoring are available both locally and through the computer. This paper will describe these features as well as the few component changes that would be required to adapt the techniques to other operating frequencies.

Effects of photoperiod on flowering and fertility of sugarcane ( Saccharum spp.)

In order to delay flowering of early clones and advance that of late ones, to permit otherwise unobtainable crosses, various photoperiod treatments were investigated. The most effective treatment to delay flowering was that in which natural induction was prevented by a night light break regime (NLB) for a predetermined duration followed by a daylength extension imitating natural inductive daylengths. Clones responded to a 10 min difference between inductive daylengths. When the NLB was followed by natural days (shorter than normal for induction) all stages of development were hastened and one clone was rendered male sterile. Periods of NLB after floral initiation in general delayed development; applied at the spikelet initiation stage, flowering of clones was delayed by 1–2 weeks and pollen fertility was reduced, but applied at the earlier stage of branch initiation, flowering of some clones was delayed whereas inflorescences of the remainder did not emerge. Flag leaves of the latter did eventually emerge and were significantly longer than those of control plants, indicative of reduced competition with the inflorescence as a result of the developmental delay. Advance of flowering in a late clone was effected by shortening daylengths by 30 min (SD) for various periods prior to and during floral development and, although the greatest advance was afforded by the continuous SD treatment, most of those for lesser periods also reduced in earlier flowering and therefore offer a more economic use of dark-room facilities when advancing late clones. The precise photoperiod control of successive developmental phase is discussed and it is conducted that sugarcane is a quantitative intermediate day plant, and that successive developmental stages have shorter less critical daylength requirements. This hypothesis is discussed in relation to flowering behaviour of sugarcane at different latitudes.

Precise Frequency and Phase Control of LSA Oscillators (Short Papers)

It is shown that consideration of both the external microwave circtuit and the dc bias applied to the diode are necessary in order to obtain satisfactory locking results with an LSA oscillator. When both are properly arranged, good control of both the operating frequency and the phase of an LSA oscillator at 3 GHz is demonstrated.