Timing performance of phased-locked loops in optical pulse position modulation communication systems

An optical digital communication system requires that an accurate clock signal be available at the receiver for proper synchronization with the transmitted signal. Phase synchronization is especially critical in M-ary pulse position modulation (PPM) systems where the optimum decision scheme is an energy detector which compares the energy in each of M time slots to decide which of M possible words was sent. Timing errors cause energy spillover into adjacent time slots (a form of intersymbol interference) so that only a portion of the signal energy may be attributed to the correct time slot. This effect decreases the effective signal, increases the effective noise, and increases the probability of error. A timing subsystem for a satellite-to-satellite optical PPM communication link is simulated. The receiver employs direct photodetection, preprocessing of the detected signal, and a phase-locked loop for timing synchronization. The variance of the relative phase error is examined under varying signal strength conditions as an indication of loop performance, and simulation results are compared to theoretical calculations

New broadband square-law detector

Compact device has wide dynamic range, accurate square-law response, good thermal stability, high-level dc output with immunity to ground-loop problems, ability to insert known time constants for radiometric applications, and fast response times compatible with computer systems

Trees of W.A. Jarrah and Karri

In commencing this series, in which a large number of trees will be dealt with, first place must be given to the species of Eucalyptus which include, besides the gum-trees, the various shrubs and mallees which make up a considerable part of the woody flora of South-Western Australia

Trees of Western Australia - the dundas mahogany

Among the most popular trees for planting in the agricultural areas is the Dundas r V mahogany which, while closely resembling the salmon gum superficially, is even more attractive because of its deeper green crown and paler-coloured bark. Like the salmon gum it thrives in low rainfall areas in loamy or sandy loamy soil

Trees of Western Australi - No. 35 - The Warted Yate, No. 36 -The Crowned Mallee , No. 37 -The Bullich, No. 38 - Bell-Fruited Mallee.

THE Warted Yate was originally discovered by the writer in 1927 in the Ravensthorpe Range, and to date it is a tree of restricted habitat in that the species has not been found occurring naturally in any other locality. ON the hills of the south coast extending from and including Middle Mount Barren and East Mount Barren, the Crowned Mallee is found in scattered spots. Originally discovered on Middle Mount Barren in 1926, it has subsequently been found in other places, principally around East Mount Barren, growing amon? quartzite rocks and attaining a height of about five feet, although usually less. In cultivation it grows somewhat taller, and has been widely cultivated in Victoria for windbreak purposes. THE name megacarpa, meaning large-fruited, is not particularly appropriate, for compared with other Western Australian species of Eucalyptus, the fruits are not large. The species takes on two distinct forms. A tree form is found mostly in wet soils in the karri and southern jarrah forests extending from Jarrahdale on the Serpentine River to the vicinity of Alb my, and also on the limestone soil of the valleys at Yallingup. A mallee form is found on the mountains of the Stirling Range, in shale and quartzite; this form is also found as far east as the Barren Hills.\u27 Both forms are attractive. THE Bell-Fruited Mallee is one of the most attractive of our small shrubby species of Eucalyptus. It is found in the south coastal districts from the west end of the Stirling Range as far eastwards as Stoke\u27s Inlet. Rarely exceeding three or four feet in height, and of untidy, straggling habit, with stiff, blunt, grey-green leaves, its shortcomings in these respects are more than outweighed by its magnificent blossoms of rich yellow, and its attractive bell-shaped fruits. It grows in poor soils, such as stony sandstone country, usually on the open heath

Trees of Western Australia - Four Bloodwoods from the Kimberley

The four bloodwoods dealt with in this article are small trees restricted to the Kimberley Division of Western Australia and include Eucalyptus latifolia, F. Muell.; Eucalyptus Folscheana, F. Muell.; Eucalyptus lamprocalyx, Blakely, and Eucalyptus Ciliftoiana, W. Fitg. They grow in sandy soil or in stony places amongst sandstone rocks and seldom exceed 40ft. in height. E. lamprocalyx and E.Ciliftoiana are little known species concerning which further information is required

Trees of Western Australia - swamp or flat topped yate, brown mallet and four-winged mallee

The two trees described here under may be readily distinguished when growing as they differ considerably in their barks and general appearance and grow under different conditions, but in common with some other trees of the Southwest each has the mallee form, and the mallee forms are very difficult to distinguish

Trees of Western Australia - salmon gum and scarlet pear gum

The name salmonophloia, meaning salmon-barked, was given to this tree in 1878 by Ferdinand Mueller, the famous Australian botanist. The title of Salmon- Barked Gum-Tree had already been bestowed upon this tree by the early settlers, a name which apparently referred to the colour of the bark in fracture when it resembles the colour of cooked salmon flesh. The external colouration varies from a brownish pink at the end of summer to almost white in winter, usually with greyish-purple patches

The Manna Wattle (Acacia microbotrya Benth)

The Manna Wattle is an attractive native tree which is worthy of attention for several reasons. Perhaps it is best known as the source of manna gum —the market value of which has risen from £170 per ton in 1955 to £252 per ton (2s. 3d. per lb.) at the present time