Surveying Instrument Collection
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Maker |
Tellurometer, South Africa |
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Model |
MRA 101 |
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Serial Number |
113 |
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Dimensions |
Length 381 mm, Width 368 mm, Height 184 mm |
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Image |
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Description |
This Tellurometer Model MRA 101 is a long-range microwave distance meter capable of measuring distances up to 50 km. Due to its large parabolic antenna (330 mm in diameter) located on the transmitter end, and a beam width of only 6°, it is also useful for accurate short-range urban applications, since the reflections from passing traffic are held to a minimum. Long range performance is of a high standard and multipath reflections are reduced. Two identical Tellurometer units are used when measuring a line, with one placed at one end of the line to be measured and the other at the opposite end. These two units are known respectively as the "Master" and the "Remote" units and each one can be switched to operate as either unit. The instrument uses microwaves (radio waves) of 10 cm wavelengths for the distance measurement, which is read at the master station. The read-out is calibrated directly in units of length. The read-out tuning knob is rotated until the pointer on an adjacent meter is brought to its centre-scale position. The actual distance being measured is then read from a circular scale in metres (coarse reading) and, by means of a vernier, in centimetres (fine reading). By operating only one switch and one read-out control, the operator can obtain a distance reading in about a minute. In favourable conditions, a distance precision of ±(1.5cm+3ppm) can be obtained. A continuous microwave carrier wave, variable within the frequency range from 10.05 to 10.45 GHz is transmitted by the master instrument and is produced by an electronic component known as a klystron. The average power consumption of the instrument is 3.2 A at 12 V. It's modulation frequency is 7.5 MHz. An interesting and highly efficient feature of this Tellurometer is that it incorporates a duplex, frequency modulated speech facility, allowing communication between the two stations simply by flicking a switch labelled "speak" located on the right of the control panel and using the headset provided with the unit. |
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History & comments |
The Tellurometer was invented by Dr. T. L. Wadley, of the South African National Institute for Telecommunications Research. The first commercial instrument, the MRA 1, was introduced in 1957. |
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Conservation |
A glass-fibre carrying case (Length 476 mm, Width 406 mm, Height 216 mm) |
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Condition |
Good |
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Remarks
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Dates |
Manufactured in 1962 (approx). Catalogued in 2000. |
