Our story commences at the end of 1942. There was much activity at Melbourne's Essendon Airport with the war in full swing, with all of the hangars actively engaged in aircraft maintenance and overhaul of both military and civil aircraft. The hangars were in use 16 to 24 hours a day, and involved the use of electric motors and arc welders. As a result, the Aeradio operators were having problems in receiving signals from aircraft because of the interference generated by industrial equipment, not only on the aerodrome but also from as far away as St Albans.

This indicated to DCA that the HF receivers on the aerodrome were no longer satisfactory, and that some remote receiving system would have to be established.

At this time, the RAAF had a receiving station at Werribee (between Melbourne and Geelong) and in an isolated area. It included a good aerial farm to the west of the station. The RAAF gave DCA permission for four AR-7 receivers to be installed in spare racks. Airways engineers Roy Hinkley, Tom Farrell and Gordon Newstead designed modifications to enable the receivers to be controlled remotely.

DCA rented from the Post Master General (PMG) two cable pairs between Essendon and Werribee. Along each of these pairs was sent the receiver audio to Essendon, and between each leg of the line and earth was a Caihlo circuit. The Caihlo enabled DC control of the receiver gain and tuning, and beat frequency oscillator (BFO) over the same line as the audio.

This arrangement worked well until 1947, but by then the PMG was unable to provide extra lines for the additional required circuits. In addition, the rental of the control lines was costly - £217 ($6,800 today) per circuit. The lines were 30 miles in length and traversed a number of telephone exchanges which made the service unreliable. Also, by now the Werribee installation had grown so much that to provide additional directional aerials was difficult. Maintenance was expensive, due to the long travel distance and time to correct faults.

At Craigieburn, about eight miles north of Essendon, the Royal Netherlands Navy had just vacated a wartime radio station which would meet DCA’s needs. The PMG’s Department could provide control lines at one third the cost of the Werribee circuits. Craigieburn became Melbourne's remote receiver station from 1949 until the present Melbourne Airport (Tullamarine) was constructed in 1967, at which time the receivers were relocated to a site on the airport.

Turning now to the transmitter arrangements, until 1947 all HF transmitters were housed in a wartime transmitter station near the Essendon Airport Control Tower. It then became necessary to relocate the facility as the 150-foot aerial masts constituted an obstruction to the approach path of the new east-west runway, which was nearing completion. (Until this time, Essendon was an ‘all-over’ field with no sealed runways). It was therefore necessary to establish a new transmitter station at a remote site. In any case, the existing building and aerial farm were too small even for present requirements, let alone future extensions required by the increase in aeronautical communications traffic at Essendon.

A site was chosen at Campbellfield on the main Sydney Road (opposite the present Ford works). It was close to high-tension power lines for the station supply, and also in the general vicinity of the Craigieburn Receiver Station. It was proposed that upon the purchase of the land, the two 150-foot masts from Essendon would be re-erected and ten 100-foot masts or towers would be installed for additional point-to-point and air-to-ground equipment. A 60-KVA Diesel electric generator, ex-RAAF transmitter station at Mt Gambier and recently purchased through Disposals, would be installed. The PMG would provide the necessary lines between Essendon and Campbellfield. The estimated cost of all this work (excluding the land) was £14,000 ($370,000).

At one stage it was proposed to extend the domestic service to International status. After much discussion Eric Anderson, the chief Communications Engineer, gave the instruction to "add fifty feet to the building", and that was that. In the event, international services did not eventuate, so DCA ended up with a half-empty building. The lino floors were dutifully polished every week by George, the Cleaner, and the station always appeared very ship-shape.

Another interesting story relates to a short-lived HF facility at Rockbank (west of Melbourne). Soon after the end of the war, Pan American was anxious to start a regular air service to Australia. At that time, there was much competition between the British and Americans to institute this service to Australia and to other locations in the area. Australia, New Zealand and Britain were also adamant about the need to have a service to the United States if Pan American was allowed to operate down through Auckland to Sydney. British Commonwealth Pacific Airlines was formed for this purpose.

Before any of these services could commence, DCA needed a liaison frequency with Honolulu, and this required a high-powered transmitter. DCA did not have access to such equipment, so they co-opted the Army to provide a Marconi 3.5KW SWB-8 at their Diggers Rest Transmitter Station. Similarly, the Army provided a receiver at their Rockbank Receiver Station. Meanwhile, DCA technicians provided a small table in the Essendon Aeradio building, and installed a microphone, Morse key, speaker, headphones and press-to-talk key to control this Honolulu circuit. There was no remote control for the receiver, and DCA had to ring the Army technicians to make any necessary adjustments. The circuit remained until 1946 and was the only overseas link for a long time.

There was a certain romance about the HF era. Rows of large transmitters with brightly-glowing valves, paddocks of aerials and feeder cables and large generators to power the equipment. And, of course, George’s polished floors.

Click here to see inside Sydney's Llandilo HF transmitter station.

Click here to read about the HF Communication Stations of Sydney.