HF Field Strength Measuring: OTC Station, Rockbank - c.1962

In about 1962 DCA took part in measurements of the field strength of the High Frequency radios at the Overseas Telecommunications Commission (OTC) Station at Rockbank, west of Melbourne. The OTC Station was established as part of the Empire communications network before the Second World War. The tests were a co-operative OTC-DCA effort which were aimed at obtaining comparative records of directivity response (polar curves) of a number of different types of HF aerial simultaneously: plain rhombic; vertically tiered rhombic; horizontal array dipoles; and uniform arrays. DCA Douglas DC-3 VH-CAO was used to fly three mile orbits around the antennas at various altitudes. A portable Australian DME system was set up in a van on site to provide continuous distance reference to the aircraft.

Ron Rye, one of the DCA Engineers involved, recalls:

"The chap standing behind the theodolite [in the photo above] is Jeff Byrne. He was not a technician but a clerk from the office whom we roped in to help with the number of hands necessary on the days of tests. Jeff had been I think a major in the Army and had that 'military bearing' and enjoyed a day out of the office. The tests measured the patterns of the short wave antennas we used in those days. The procedure was much the same as testing the Radio Ranges - the DC-3 flew 3 naut. mile radius orbits at various heights radiating a signal which was picked up on chart recorders with calibrated moving pen and paper rolls. Geoff clicked a button every 10 degrees to put a reference mark on the moving charts (in the navaid case the transmitter was on the ground and receiverr in the aircraft). The blokes in background are linesmen trained to climb up the masts and alter the rigging of the short wave antennas when required. Similar to overhead line work done by telegraph linesmen. The tests were of some international interest because we had the opportunity to do them without financial restrictions which existed elsewhere and hit us a few years later."

The field strengths measured were transmitted to the ground where the data was plotted using a pen-recorder mounted, along with other test equipment, in the back of the van at left in the photo above.

The photo at left shows Pat Davison marking the pen-recorder chart while Bill Sanders (L) and Ron Rye (R) look on. All three were DCA personnel: Pat Davison and Ron Rye were Central Office Engineers whilst Bill Sanders was a technician.


The photo below shows the test gear in the back of the van, looking rearwards. On the left is a pen-recorder. As data came in, a pen would move tansversely across the paper in response to the incoming signal. At the same time, the paper chart would be wound on from top to bottom, thus producing a record of the input signal over time. Next along is an Amalgamated Wireless Australasia (AWA) Low Frequency Field Intensity Meter Type A55131 (DCA ident Y/7029), Serial No 15. Next is another pen-recorder and following that a Palec Signal Generator sitting atop another A55131 Low Frequency Field Intensity Meter, Serial No 8. Lastly (and out of sight in this shot) is another pen-recorder.

pen-recorderA55131 LF Field Intensity Meterpen-recorderPales Signal GeneratorA55131 LF Field Intensity Meter

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(Photos: Ron Rye collection)


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