Sea Paths Research Articles

Propagation of metric waves beyond optical range

A qualitative survey of tropospheric and ionospheric propagation in the frequency band 30-200 Mc/s. Theoretical considerations are limited to explanations of the basic principles involved.A knowledge of the easily recognized meteorological conditions associated with variations in tropospheric propagation is shown to be useful in short-term prediction of radio conditions. Owing to the random nature of such conditions, however, the extended ranges obtained will, in general, be disadvantageous because of interference problems between fairly widely separated transmitters.A selection of long-term observations over various land and sea paths, both tropospheric and ionospheric, is presented in graphical form and results discussed.

The measurement of the velocity of propagation of centimetre radio waves as a function of height above the Earth. Part 2: The measurement of the velocity of propagation over a path between ground and aircraft at 10,000, 20,000 and 30,000 ft

Part 1 of the paper gave an account of the measurement of the velocity of propagation of centimetre waves over a sea path at low level, and concluded that the velocity is 186,217±16 miles/sec. Part 2 gives the results of experimental flights observed from two Oboe ground stations in order to measure the velocity of propagation as a function of height above the earth. The results indicate higher velocities than those previously calculated. The most probable values for the mean velocity of propagation between ground and aircraft at 10,000, 20,000 and 30,000 ft are 186,233, 186,246 and 186,256 miles/sec respectively, the metric equivalents being 299,713, 299,733 and 299,750 km/sec respectively.

Calculation of Ground-Wave Field Strength over a Composite Land and Sea Path

A brief discussion of the problem is given, together with a description of the three proposed methods of solution. The results of a practical experiment are shown, and curves calculated by the three methods are compared with the observed results. It is shown that the BBC method gives field strengths much nearer to the observed values than the P. P. Eckersley method, and that the method proposed by Millington, while somewhat more laborious to use, also gives results which agree well with observed values. The difference between the three methods is small at low frequencies and when the effect of the discontinuity is not large.

The measurement of the velocity of propagation of centimetre radio waves as a function of height above the Earth. Part 1: Ground-level measurements of the velocity of propagation over a sea path

The Oboe blind-bombing system probably provides the most accurate radar range-measuring system to date. The system has been used to measure the velocity of propagation of centimetre waves over sea and land paths at low level, in addition to paths between ground and aircraft at 10,000, 20,000 and 30,000 ft. The paper describes the experiments over a sea path between two shore-based stations each situated at a height of about 400 ft. The results give a value of 186,218±15 miles/sec for 9-cm waves over a 40-mile path. A subsidiary check over a 30-mile path gave a figure of 186,216.5±17 miles/sec. It is concluded that the final result is 186,217±16 miles/sec. Using a conversion factor of 1 m = 3.280843 ft, this is equivalent to 299,687±25 km/sec.

Discussion on “Accurate measurement of the group velocity of radio waves in the atmosphere, using radar technique”, “A method of determining the velocity of radio waves over land on frequencies near 100 kc/s” and “The measurement of the velocity of propagation of centimetre radio waves as a function of height above the Earth. Part 1: Ground-level measurements of the velocity

Discussion on “Accurate measurement of the group velocity of radio waves in the atmosphere, using radar technique”, “A method of determining the velocity of radio waves over land on frequencies near 100 kc/s” and “The measurement of the velocity of propagation of centimetre radio waves as a function of height above the Earth. Part 1: Ground-level measurements of the velocity

The authors' reply to the discussion on “Accurate measurement of the group velocity of radio waves in the atmosphere, using radar technique”, on “A method of determining the velocity of radio waves over land on frequencies near 100 kc/s” and on “The measurement of the velocity of propagation of centimetre radio waves as a function of height above the Earth.

The authors' reply to the discussion on “Accurate measurement of the group velocity of radio waves in the atmosphere, using radar technique”, on “A method of determining the velocity of radio waves over land on frequencies near 100 kc/s” and on “The measurement of the velocity of propagation of centimetre radio waves as a function of height above the Earth.

Experimental studies of the propagation of very short radio waves

The paper presents a survey of the experimental work on the propagation of very short waves, and especially of centimetre waves, carried out in this country during the war. Although much of the paper is necessarily descriptive, and by no means all the problems are solved, it has been written with the aim of providing the radio engineer with applicable results where they have been established.After referring to the main differences in propagation characteristics between these waves and longer radio ground-waves, the state of the art at the beginning of the war is briefly noted and the development of the war-time experimental work is outlined. Some simple theoretical characteristics are then described to provide a background for the experimental results which follow.Preliminary experimental studies over land and sea paths are described, with a summary of the tentative conclusions to which they led. The main experimental programme consisted of measurements of 3-cm, 9-cm, and 3½-m waves over sea paths 57 miles and 200 miles in length; and of 9-cm waves over a single 38-mile land path. The measurements were continuous over some of these paths for periods between two and three years; and, particularly as regards detailed correlation with meteorological measurements, the work is still in progress.In a concluding Section some investigations into special aspects of very-short-wave propagation are described; data on reflection from sea and land, and on the effect of obstacles, are included in this Section.