FM in VK6 before voice repeaters were established


Going Mobile

The introduction of FM in Australia and in particular VK6 was due to the desire by amateurs to go mobile. Many amateurs post WW2 had done so on a variety of bands from 160 metres to UHF. The limiting factor was cheap easily available equipment, apart from the difficulty that valve technology introduced.

Post WW2 there was a variety of equipment available, but it was not until commercial mobile VHF was introduced in the 1950s, and some of these commercial mobile radios became available on the surplus market, that mobile amateur radio expanded.

The early commercial mobile radios were Amplitude modulated (AM) such as the Pye reporter and with radios like the Pye Reporter, amateurs in VK6 started going VHF mobile, in particular on 6M. Amateurs had to wait for these expensive radios to become partly obsolete in the commercial World  before they could be purchased on the surplus market. Radios went for many pounds in the 60s, a couple of hundred dollars in todays money, and they were not always easy to find.

These mobile radios of the 1960s were almost always valve with their associated high voltage power supplies. Transistors had started to appear but these few early radios, such as the Philips 1680, were rare and expensive on the surplus market. You could pay $100, about $900 in todays money (2017) for a single channel transistor mobile.

Ron VK6PR was the first to have a Philips 1680. The audio sounded great with a good communications punch to it. Not having to worry about leaving the mobile turned on in the car, with the associated flat battery next morning, was a major plus.

Pye Reporter VHF mobile am transceiver
Pye Reporter VHF AM mobile transceiver

Pye FM Ranger FM transceiver
Pye FM Ranger FM mobile transceiver

Valves and more valves
RF output was a QQV03-10


In VK6 the availability of ex-commercial FM mobile radios gained speed in the late 1960s. Valve radios like the Pye FM Ranger shown above could be purchased for about $20 ($200 in todays money-2017) and fairly easily converted to 2M FM. These radios were wide band FM (15KHz typical) and were used as such. The more deviation that the receiver could handle, without exceeding the IF band pass, the better signal to noise and the less ignition noise problems while mobile. FM has a great advantage over AM in its ability to be fairly immune to pulse type noise but not entirely. The Pye Ranger had a TX power typically of 10 watts and was used by many VK6 amateurs to get them onto VHF, both as a home base station and as a mobile.

My Pye FM Ranger..An introduction to Amateur Radio..

For me my introduction to amateur radio in 1971 was with a Pye FM Ranger. I had not been on air yet, and this was all very exciting.

These transceivers were mainly valve, with a transistor DC to DC converter for the high voltage. Conversion to the amateur band required a degree of knowledge about how such a transceiver worked. The transceiver required a new crystal for the receiver and the transmitter and realignment to 2 metres.

I built a range of test equipment in order to get the radio working.....

A signal source using the TX crystal as an oscillator. The crystal was on a much lower frequency and multiplied up to 2 metres. The harmonic from the oscillator made an ideal signal source of about 100uV on 2 metres..

A step attenuator to reduce the signal source level.

A 50 Ohm power dummy load.

A VHF SWR meter.

Most of these designs came from Electronics Australia who had many Amateur Radio projects in those days.

The antenna was a drooping radial 1/4 wave up about 15 feet.

All activity was on 146.000 MHz.

As with everyone the first contact with another amateur is amazing. Mine was to Russ VK6CV who was mobile. The first thing Russ said was turn the FM deviation all the way up. At the back right hand corner there is a potentiometer, just turn it all the way clockwise. The FM deviation was now 15 KHz...

So began my introduction to amateur radio....

Later modifications to the FM ranger was a S meter, dual gate MosFet preamp and a separated DC to DC inverter to increase the TX final plate voltage from 250 volts to 400 volts. This increased power output from 10 watts to 17 watts...!

VK6UU Log Book...1971

Without talk-through repeaters yet in VK6, amateurs worked hard to get the most from their mobile installation. Making sure the radio was as good as it could be, along with a good mobile antenna installation, surprising distances were regularly worked mobile to base and mobile to mobile. Emphasis was mainly on getting the receiver working as well as it could. Even realignment of the IF (intermediate frequency) was done to reduce ignition noise. If the IF is not flat across its passband then ignition noise increases due to phase distortion. FM is not completely immune to ignition noise.

Typical home brew mobile antennas were the 1/4 wave and the 5/8 wave. Both required a good mobile ground plane on the vehicle for best results and experimentation was with various locations to mount the antenna. When you are dealing with weak mobile to mobile signals every improvement, no matter how small, made a difference.

The FT-2Fb 2M FM Transceiver
First Amateur transistorised 2M mobile FT-2FB

When the first fully transistorised 2M FM amateur mobile came on the market in the early 1970s, it was what most wanted to own. No large current hungry valve mobile radio but a 12 channel radio that was easy to mount in the vehicle and instant on, no waiting for valve filaments to heat up.

The Yaesu FT-2FB was a 12 channel crystal locked 10 watt transceiver that sold for $400 give or take. That is around $2,000 in todays money...! The first one in VK6 was owned by Jim VK6RU (SK). Jim could be heard most mornings and evening driving to and from work using his FT-2FB, and Jim did not have to worry about leaving the radio on in the car and flattening the battery, like valve mobiles did regularly.

Technology has come a very long way for many of us who are of the valve era.

Frequencies used for FM on 2M

146.00MHz was the frequency used on 2M for FM. All radios way back then in the 1970s were crystal controlled and each channel required two crystals, one for receive and one for transmit. At $100 for a pair (in todays money) few radios had more than one channel.

The allocated channels for FM on 2M were....

Channel A 145.854 MHz
Channel B 146.000 MHz
Channel C 146.146 MHz

Note Channel A & C were 146 kHz lower & higher than the main channel 146.000 MHz.

Channel A & C were rarely used if at all. With the cost and difficulty of adding more channels, as the X commercial radios were single channel and you had to add your own channel change switching, most FM activity was on 146.000 MHz.

Note also the 3 channels were close together. This was because it was thought that the X commercial radios had a narrow RF front end bandpass, and as you moved away from the frequency the radio was tuned to, performance would degrade. Don't know if this was true but it was the reason for the three 2 metres channels being close to one another.

Vertical Polarization

FM operation on 2 metres was not the first use of the 2 metre band in VK6 by a long way. Many dedicated amateurs had made the jump from 6 metres AM to 2 metres AM using in most situations, home brew equipment.

This 2 metre operating used horizontal polarization. The antennas usually a Yagi. When FM appeared on 2 metres, vertical polarization was chosen as it was the easiest to install on a vehicle. Home stations using 2 metres FM also used vertical polarization so as to work mobile stations.


Talking about a Repeater

Talk-through voice repeaters had been operational in the amateur World since the 1960s and Australia's first 2M amateur voice repeater was at Orange in NSW. Much discussion was taking place in VK6 as to building and operating a repeater but the lack of information and limited communications (there was no Internet) made the going difficult.

Just what equipment to use was a major issue, as way back in the late 1960s, there were few options. Much concern at just how good the equipment had to be so as to work without desensing was largely unknown, at least in VK6.

Not all amateurs active on 2M FM thought that talk-through repeaters were necessarily a good thing. Some amateurs could see that a talk-through repeater just made it too easy and the attention to detail at operating a good mobile or base station would fall by the way. An opinion perhaps held by some today.

Repeaters on air

When repeaters were first licensed by the PMG in the late 1960's, they used a 500KHz split and their respective in and out frequencies were either side of 146MHz. I think there were only 4 channels.

About 1971 the split was changed to 600KHz to be the same as in the U.S. and the repeater band was moved into the 146 to 147 segment, all with the same -ve offset. There was only 8 channels. There was no repeater band above 147MHz, hence there was no +ve offset. These 8 channels were called channel 1 through 8.

The repeater segment above 147 came into use in the late 1970's from memory, and used the +ve offset. The reason for the +ve offset I'm not sure of.

This history of development tends to result in city repeaters, which were established first, having a -ve offset and country repeaters a +ve offset.