A few thoughts about Early VHF activity in
VK6 By Don Graham VK6HK
I can’t speak from personal experience before my VHF SWL days from 1948, but word has it that there was significant activity on the then allocated 56 MHz band pre WW2. Transmitters were often of the AM modulated oscillator type with superregenerative receivers. There were exceptions; one I know about was the crystal controlled AM transmitter of Jack Gabbertas VK6GB (SK). After WW2 Jack resurrected this tx from the care of the Post Office whence it had been quarantined during the war and retuned it to 50 MHz.
Post WW2 saw a new approach. There was considerable interest generated around 1947-1948 by the availability through disposals of numbers of crystal controlled RAAF aircraft equipment type SCR522.
SCR522
These were originally multichannel crystal controlled rigs with a mechanically complex channel changing system, operating around 100-150 MHz. They were universally modified to a single channel 144 MHz AM transmitter with the superhet receiver converted to variable tuning with a free running local oscillator. The receiver IF bandwidth was something like 150 KHz, so drift and transmitter netting issues due to dubiously accurate crystals were not much of a problem. A well populated net was established with operation mainly concerned with simplex ragchewing or as a local liaison for HF DX chasing. There was some interest in seeking longer DX paths on 2mx; e.g. a Dxpedition was undertaken to none other than Mt William when Ron VK6KW(SK) worked Jim VK6RU(SK) back at his home QTH in Perth. Amongst other operators on the net were VK6WT, 6GB and 6AG (All SK).
At about the same time there was a different bunch of people who started looking at exploiting the possibilities of weak signal and ionospheric DX work in the newly allocated 50-54 Mhz band (which replaced the prewar 56 MHz allocation). These included VK6GB (SK), VK6LW (SK), VK6RK (SK), VK6BK, VK6FC (SK), VK6HM and in the country VK6DW (SK) at Bruce Rock, VK6GS (SK)at Harvey and VK6WU at Wubin. These efforts all used home built AM transmitters and often the receivers too. Typical contacts were confined to locals and shorter range tropo DX until November 1948 when the first interstate contacts were made on 50 MHz from Perth to Adelaide. So far as VK6 was concerned these had been preceded by the efforts of VK6HM who by then had moved to Kalgoorlie and made interstate contacts a little earlier. Chas VK6HM later moved again with DCA to Cocos Island where he continued to operate 50 MHz as VK1HM (as it was allocated in those days before Canberra enjoyed a separate prefix) but without any known success.
It should be mentioned that around 1948 Frank Clarke VK6FC also used FM and stable VFO control on 50 MHz. Something considered very advanced for the day. Another experimenter into FM was Blake Horrocks VK6GS who constructed an ingenious wide band crystal controlled FM exciter from which he produced deviations on 50 MHz of the order of +/- 100 KHz odd. Sadly there were no receivers around that could take advantage of this as the usual method of dealing with any FM transmissions was slope detection.
Apart from the aforementioned use of SCR522 gear on 2mx, weak signal work on 144, particularly with narrower band, more sensitive AM receivers was a little slower to get going. All such gear had to be home built as there was no commercially made equipment for amateur use around on those frequencies. However by the early 1950’s activity began to increase. A “big advance” was the appearance of “crystal controlled converters” operating in front of HF communications style receivers. Tuning the band was accomplished at IF and all the facilities of the HF receiver were available, such as narrow IF, CW operation etc. Operationally, nets did not exist as such. Each station usually set up their own crystal locked transmit channel and to make other than a prearranged contact it was necessary to call “CQ” and then tune the band for any reply.
Similar techniques prevailed on 50 MHz at this time and by 1951 interstate contacts to all call areas were becoming “almost” routine. However a big cause for excitement in late 1951 was the first recorded interstate contacts from Perth on 2mx AM by VK6BO to VK5QR and 5GL, but it was to be decades before the experience was to be repeated. Major parts of the gear for these contacts was home built.
At this stage there was also some experimenting going on with the then allocated 288MHz band, particularly by VK6BO (SK) and VK6GB (SK) using crystal controlled gear and by others with simple modulated oscillators and superregenerative receivers.
1954 saw a major boost to activity with the advent of the first non CW licence; i.e. the “Z” call. This allowed only operation on 2mx and above and many took up the opportunity. The first contact made in VK6 under the new licence was by Cec VK6ZAZ, better known as VK6AO today. Valve technology was still much the same with steady refinements in antennas, higher power, better receivers etc but all still based on the AM mode for telephony.
Around this time there appeared an increased interest in mobile or portable operation. Still however with AM technology and home brew transmitters and receivers aided sometimes by partial conversion of disposals gear like the “Command” series of airborne receivers in one example of a 2mx setup. This gear was always tuneable; well, at least the receiver was. Another adaption was to use an existing car radio as the tuneable IF following a crystal locked converter (on 50 MHz in one case). There was still no commercially made equipment for amateur base or mobile application.
Until… in the early 60’s there started to appear on the scene from disposals sources some of the early commercial gear made for FM operation in the 70 MHz range. It was possible to retune this for 50 MHz and a two frequency simplex net system quickly grew in popularity. This was later followed by the availability of ex commercial “high band” FM transceivers which were tuneable to the 2mx band and rumblings about the need for a repeater were to be heard. I believe that the first efforts to bring this to fruition were made by Mac VK6MM and Graham Byass then VK6Z? later VK6BY.
By the end of the decade there was another “newby” in the offing in the form of SSB. Initially commercial gear was not to be had; certainly not for VHF and it was another case of having to “roll your own”. First pioneers on VHF SSB in VK6 were Mac VK6MM and Wal Howse then VK6ZAA, both on 50 MHz. Today, AM is of course no more, with several solid state SSB transceivers commercially available using technology which would have been considered science fiction in the 1950’s.
Don VK6HK