Chapter 6: The Birth of the Instrument Section (continued)

We arranged for a contract to be arranged for the modification of oxygen cylinders for use as hydrogen generators. That saved the day because it was the only way to obtain a supply of hydrogen.

It was also necessary to have balloons made for radiosonde flights. Again Alan Martin was a great help in solving this problem. Ansell were making toy balloons but we wanted these big six-foot (two metre) balloons. Martin was a better chemist than I. He did a lot of work in designing a system to use the Ansell equipment to make large latex radiosonde balloons. Ansell was given the contract for their manufacture.

The original radiosonde ground equipment was based on a super-regenerative receiver supplied by Friez. We imported one radiosonde transmitter for examination by PMG research. There were a number of different radiosonde designs world-wide at this time. Some worked on variable radio frequencies to measure temperature and pressure. Some worked on variable audio frequency. A Finnish one worked on a chronometric type of delay. The time between signals was the measure. There were various types.

In the Diamond-Hinman type of radiosonde an aneroid cell drove a contact over a commutator which switched in a cycle of temperature, relative humidity and reference. Pressure was calibrated in millibars at each switching position.

The design of the commutator strip was about three inches long made up of alternate metal and insulator segments and that had to be produced and individually calibrated. It was hooked up to an aneroid capsule (with thermal compensation built in) which drove a wiper across the commutator.

As the wiper moved it switched from a contact to a no-contact. Contacts provided measurements of temperature and humidity. Because of drift due to battery changes a reference point was needed; so every fifth contact had a standard resistor attached that sent a standard signal.

Bureau of Meteorology