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Vintage Radio
By RODNEY CHAMPNESS, VK3UG
Outback communications: the
Flying Doctor radios
Radio communications played a vital role
in bringing the Flying Doctor service to the
outback. Here’s how the outback radios were
developed.
Back in 1912, the Reverend John
Flynn became acutely aware of the
needs of people living in outback Australia. The community facilities that
we now take for granted in our cities
– ie, good roads, rapid transport, good
medical services, communications
(including telephones), entertainment
and supermarkets, etc – simply did not
exist in the outback back then (and
Alfred Traeger posing with the first pedal radio in November 1928. This
consisted of a 2-valve regenerative receiver using space charge tetrode valves
(A141) and a 1-valve triode (B205) crystal-controlled Morse code (CW)
transmitter. The transmitter operated with an output of 1-1.5W on a frequency
of 2230kHz.
82 Silicon Chip
often still don’t today).
Admittedly, many of these facilities
were rudimentary – and in some cases
non-existent – in city areas in 1912.
However, the people of the outback
had none of these conveniences. How
would we like to live in a world like
that?
In reality, the infrastructure in outback Australia is quite poor and, given
the sparse population, will remain
that way.
Flynn, through the Australian Inland Mission (AIM), an arm of the
Presbyterian Church in Australia,
began looking at ways to address the
plight of people in isolated outback
areas. In particular, he saw that people
needed medical facilities (hospitals,
doctors and nurses), the means to obtain speedy access to these facilities,
and a means of calling promptly for
this assistance.
The few medical centres that did
exist at that time were thinly spread
throughout remote areas. A single
nurse (or perhaps two) and – if they
were lucky – a doctor within a few
hundred miles were about the best that
people in the outback could expect
nearly a century ago.
Transport to and from these centres
was also a very real problem in those
days, as the best roads were often little
better than two wheel ruts through the
scrub. Flynn was convinced by 1917
that aircraft could ultimately provide
the needed transport in emergency
medical cases. The cost of landing
strips was much lower than providing
roads and aircraft were speedier than
land-based vehicles.
Bush radio
Another problem was that a means
of quickly summoning aid was not
siliconchip.com.au
John Flynn (nearest to camera) and George Towns setting off from Adelaide
on their 1925 trip to test radio communications equipment in outback central
Australia.
available. There were no telephones
back then, as the cost of providing a
telephone service to outback cattle
stations was prohibitive. In addition,
cattle drovers were never in one place
for long, so a telephone service would
have been useless for many people
anyway.
By 1919, Flynn hit on the idea of
using radio communications to summon aid in an emergency. However,
he could see that radio was still in its
infancy and not really suitable at that
stage for the job.
The world was just recovering from
the ravages of World War I and many
things were still in a state of confusion.
Spark wireless transmitting and crystal receiving equipment was totally
unsuitable for use between outback
cattle stations and the nearest town
where medical facilities were available, such as Cloncurry or Oodnadatta.
The government had also placed some
restrictions on the use of valves by
radio experimenters, although this was
gradually being relaxed.
In fact, by 1919, valves were being used in an increasing number of
transmitters and receivers and valveequipment was showing promise as a
possible solution to his problems. But
even the most advanced cutting-edge
radio technology of 1919 was still
totally unsuitable for the work that
Flynn envisaged.
As a result, Flynn encouraged both
siliconchip.com.au
individuals and groups involved in
wireless communications – such as
the Wireless Institute of Australia – to
develop an easy-to-operate, portable
or semi-fixed radio transmitter and
receiver for use in the outback. This
equipment was to be used on remote
cattle or sheep stations to communicate with a central base station.
Many tried and failed and even the
military, despite all the facilities they
had at their disposal, had nothing like
the equipment Flynn required. Was he
asking the impossible?
Early experiments
Despite those early setbacks, Flynn
continued to encourage experimenters to develop suitable radio communications equipment. In 1925, he
obtained help from Harry Kauper to
develop equipment to test various
ideas on outback communications.
Kauper was the chief engineer of
radio station 5CL and arguably the
most competent radio experimenter
in Adelaide at that time.
Under his guidance, Flynn and
George Towns (an ex-WWI digger
with experience in wireless) built the
equipment. The amount of equipment
involved can be seen in the accompanying photograph of Flynn and Towns
leaving Adelaide in the overloaded
Dodge buckboard.
This equipment was tested by Flynn
and Towns throughout the outback and
they were able to contact Kauper and
other experimenters. The experiments
were successful in that some ideas
were definitely worth incorporating
into a portable transmitter/receiver,
while others required further development. And of course, some ideas
proved to be failures.
However, the overall development
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January 2005 83
The 1930 pedal radio was built into a heavy metal cabinet and used two
transmitters – one on 2020kHz and the other on 8630kHz. This set was the
Augustus Downs pedal radio and is now at John Flynn Place, Cloncurry.
An under chassis view of the 1930 pedal radio. The transmitters used A615
valves (or A415s) and had an RF output power of just 1.5W.
direction was slowly evolving. For
example, it quickly became painfully
obvious that voice communications
were out of the question with the portable equipment envisaged. However,
Morse code transmission from portable stations would be practical within
a few years, once a range of problems
had been overcome.
In 1926, Kauper built three transmitter/receiver sets for use in experiments between Arltunga, Hermannsburg and the AWA-supplied
base station at Stuart (Alice Springs).
These were tested by Flynn and Alfred
Traeger (the pedal radio man) and
proved successful, the unit operating
for several months before breaking
down.
Inside view of the first pedal radio,
complete with all the batteries. Note
that the transmitting valve (B205) is
missing from its socket at the bottom
left of the photograph.
84 Silicon Chip
The birth of pedal radio
With the design criteria sorted out,
Flynn gave Traeger the job of developing a suitable transmitter/receiver un-
der the watchful eye of Harry Kauper
(Traeger’s mentor), who contributed
his considerable skills to the design.
After many experiments, Traeger built
the first pedal radio and unveiled
it to Flynn in November 1928. This
was a magnificent achievement, as it
was the first portable high-frequency
(HF) transmitter/receiver in the world
that could be used by non-technical
people.
According to its operating licence,
the transmitter was crystal-locked on
2230kHz. It used a B205 valve which
was operated in class “C” mode as a
Morse code (CW) transmitter. Now
the efficiency of small battery valves
was quite low in class “C”, so an
input of about 4W gave just 1.5W of
output power – ie, it was only 40%
efficient.
The low-tension “A” battery supply
came from two No.6 cells in series,
while the high-tension “B” supply
was nominally 180V but depended on
how quickly the operator pedalled the
generator (hence the name pedal radio)
which supplied this power.
The transmitter was coupled to a
quarter-wave wire aerial and a tuned
counterpoise system. This proved to be
an extremely effective antenna system,
which it needed to be, considering the
low transmitter power and the long
distances over which the equipment
was required to operate. In fact, this
type of system was used up until relatively recent times.
The receiver was a simple 2-valve
unit. It consisted of a regenerative
detector and a transformer-coupled
audio output stage which fed a pair
of headphones. It tuned the broadcast
band and one shortwave band, which
included 2230kHz.
The valves used were two A141
space charge tetrodes which required
1.5V (“A”) for the filaments and 9V
(“B”) – from two 4.5V bias batteries – for the high tension. The very
low voltage on the “B” supply was
sufficient for the A141 valves, which
were designed to operate effectively
on voltages from 2-20V.
Kauper selected the A141 valves
because they drew very little current
at low voltages. High voltage dry
batteries of the era deteriorated very
quickly in sub-tropical environments
where these sets were to operate, such
as Cloncurry in Queensland.
Six such sets were installed during
1929 within a radius of 600km of the
siliconchip.com.au
Base transmitter
The Cloncurry base transmitter
was much more powerful than the
pedal radios, having an output power
of 50W on (AM) voice. Of course, fixed
base transmitters of reasonable power
drew considerably more electrical
power than a pedal radio transmitter.
However, this wasn’t a problem in this
case, as a 32V lighting plant had been
installed at Cloncurry to power the base
station (despite the expense).
The base station receivers were also
more elaborate than the pedal radio
receivers, mainly because they had to
be more sensitive.
Teething problems
Despite quickly proving their worth,
practical experience with the new radios during the first few months also
revealed some shortcomings. In particular, the sets were not always able to
achieve reliable communications. To
achieve that goal, it was evident that
a frequency near 10MHz was needed
in addition to 2MHz.
It was a case of going back to the
drawing board and making the necessary improvements so that the pedal
radios would be effective. Although
the pedal generator had proved quite
satisfactory, the receiver lacked gain
and stability, and it seems that the
transmitter valve may not have been
rugged enough to stand the physical
abuse of being bumped around in the
outback.
As a result, these first six sets were
scrapped over a period of time and
their parts used in later improved sets,
which is why there are no examples of
the original sets in existence. However,
there are two photographs which do
show what they looked like.
The 1930 pedal radio
Harry Kauper decided to move to
Melbourne in 1930, which meant
that he was now able to provide only
limited assistance to Alfred Traeger.
Left largely to his own devices, Traeger used the best design aspects of the
original sets and worked on methods
of overcoming the weaknesses.
The replacement sets were built
into a heavy metal case (to thwart
termites) and the original single
siliconchip.com.au
Fig.1: this is the circuit for the 1930-model pedal radio. Note the two almost identical transmitter stages based on A615 valves (one for 2020kHz and the
other for 8630kHz). The receiver used three A109 triode valves – a regenerative detector and two transformer-coupled audio stages. The receiver tuned the
broadcast band and up to around 10MHz, using plug-in coils.
Cloncurry base. They quickly proved
their worth when it came to saving
lives, by summoning aircraft to carry
patients to the hospital at Cloncurry.
January 2005 85
A model 36 pedal radio with pedal generator mounted below it, on display at
“Adelaide House” in Alice Springs.
transmitter became two transmitters –
one on a frequency of 2020kHz (night
frequency) and the other on 8630kHz
(day frequency). Exactly when these
frequencies were issued is uncertain
but it was definitely by 1931.
Traeger reasoned that by having two
transmitters, communications with
Cloncurry could be achieved either
on the night frequency or the day frequency, even if one broke down. The
transmitter design remained essentially
the same as before, except the valves
used were now A615s (or even A415s),
which required four or five No.6 cells in
series to power the filaments. The radio
frequency (RF) output power remained
at about 1.5W.
The antenna design also remained
much the same as for the original set
but it was now expected to operate on
the two frequencies. As a result, two
separate counterpoises were used in
these units.
Initially, they were tuned in the
same way as the original pedal radios,
by laboriously adjusting the length
of each counterpoise. Later on, they
were modified so that the electrical
length (and hence the tuning) of each
counterpoise could be adjusted within
the set itself.
Developed in 1931,
Traeger’s Morse typewriter
sent perfect Morse code,
regardless of the skills of
the operator.
86 Silicon Chip
No meters were used in the transmitters to indicate the correct tuning. Instead, tuning was carried out by watching a small pea lamp and adjusting the
transmitter and counterpoise controls
for maximum lamp brightness.
It was said that if you got a glimmer
out of the pea lamp, you had succeeded
in tuning the transmitter!
The receiver, although also basically
the same as the original, now boasted
three conventional A109 triode valves.
There was a regenerative detector and
two transformer-coupled audio stages,
with the output stage feeding a pair
of headphones or, if the signals were
really strong, a loudspeaker.
The receiver was able to tune the
broadcast band and up to around
10MHz using plug-in coils. It was a
much better performer than the original but now required a 45V HT battery
in lieu of the 9V HT battery used in
the original receiver.
To the best of my knowledge, there
is only one example of this model
in existence and it is housed at John
Flynn Place in Cloncurry. Another set
that appears to be the same is at the
RFDS base in Alice Springs. However,
this is a model 34, which was made
around three years later and uses different valves – three 30s in the receiver
and two 33s in the transmitters.
Gaining access to these sets is difficult but I was able to see them some
years ago thanks to the late Reverend
Fred McKay. Unfortunately, I was unable to test them but I did build replica
transmitters similar to the sets at John
Flynn Place and in Alice Springs, in
order to assess their performance (the
receivers were conventional for their
era, so I didn’t build any replicas of
these).
The accompanying photographs
show the construction of the set at
Cloncurry. The “chassis” is ebonite
and components are mounted on it
as shown. The wiring is in dark red
spaghetti-covered single conductor
wire.
The transmit/receive switch is the
very large and relatively complex
unit in the centre back of the set. Its
operation can be traced in the circuit
diagram. It’s also worth noting that
Traeger made any special switches
himself.
The meter on the front panel was
used when adjusting the filament voltages on the transmitter and the receiver
valves. In practice, the receiver valves
siliconchip.com.au
Fig.2: the model 36 was the first AM/CW pedal radio to be produced in any quantity. It was supplied with three plugin transmitter assemblies (one for each frequency) and also used plug-in coils in the receiver.
were adjusted for a voltage of 1-1.3V
and the transmitter valves for 6V.
The Morse typewriter
The next improvement in outback
communications came with the development of the ingenious Morse
typewriter by Traeger in 1931. As
might be expected, the Morse code
skills of the operators at the cattle stations were generally quite poor and it
was often quite difficult for the base
station operator to understand what
was being sent.
By contrast, the typewriter sent
perfect Morse code and even had a
mechanical interlock which prevented
more than one key from being pressed
siliconchip.com.au
at a time. The exact sending speed was
adjusted by an oil-filled dashpot and
this was usually set to give a transmission speed of 10 words per minute.
Traeger could see that this valve
could also perform as a push-pull class
“B” modulator for the plate and screen
The first voice pedal radios
Voice communication was still the
goal as far as Flynn was concerned,
however.
By 1934, the type 19 valve was
available in reasonable quantities in
Australia. This valve was originally
designed for use as a class “B” pushpull audio output stage and was capable of around 2.2W with 135V of plate
voltage. With this valve, battery receivers were capable of audio outputs that
rivalled many mains-operated sets.
January 2005 87
Photo Gallery: General Electric 1934
Duette (Made by AWA)
total. However, from my research, it
would appear that a model 35 was the
first of the AM/CW sets and there may
have only been one or two of these
produced. It had a 3-valve receiver
similar to the early CW-only receivers and a transmitter similar to the
later 36 set.
The 36 set, which was produced in
late 1935 or early 1936, had a totally
new receiver. Some of the new lowfilament current tetrode RF valves
found favour with Traeger and the
new receiver had a 32 as an untuned
RF amplifier, followed by a 32 as a
regenerative detector. A 30 triode
was used as an audio stage and this
was transformer-coupled to a triodeconnected 49 audio output stage.
This set had an advantage over the
earlier regenerative receivers in that
the regeneration was not affected by
the style of antenna connected to it.
As a result, the regeneration control
was much smoother.
A design similar to this receiver
was published in the April 1929 issue of “QST”, the official magazine
of the American Radio Relay League.
However, it used valves with higher
filament current drains, which were
unsuitable for the pedal radio designs
of 1929.
Plug-in coils
Manufactured under licence in 1934 by AWA, the GE “Duette” was a
5-valve reflexed superhet receiver that was electrically equivalent to
the AWA Radiolette Model 27. The valve line-up was as follows: 78
RF amplifier, 6A7 frequency changer, 6B7 reflexed IF/audio amplifier/detector/AVC rectifier, 42 audio output and 80 rectifier. Photo:
Historical Radio Society of Australia, Inc.
of the transmitter output valve (33).
This was tried and proved successful,
even with 180V on the 19 valve – well
above its design ratings. Its standing
current was 20mA instead of 10mA in
this situation, with zero bias.
This mistreatment seems to have
been tolerated by the valve because of
the intermittent nature of transmitting.
The base station operators also used
to do routine visits to the various outstations and replaced any weak valves
in the transmitters on a regular basis
to keep failure rates down
Perhaps one point needs to be made
quite clear – the pedal generators did
88 Silicon Chip
not produce more than 220V (when
pedalling hard) and supplied between
160V and 200V (depending on the
version of the pedal generator used)
at normal pedalling rates. If they had
produced the 350V some texts suggest, transmitting valves such as the
19 (with a maximum design rating
of 135V) and the 33 (rated at 180V)
would have failed spectacularly
within seconds.
The model 36
The model 36 was the first AM/
CW pedal radio to be produced in
any quantity – perhaps 10-20 sets in
The 36 also included an innovation
that had started to appear in the last
of the CW transceivers – ie, plug-in
transmitter assemblies for each frequency (this in addition to plug-in
coils for the receiver). Changing the
transmitter frequency was simply a
matter of changing the pre-tuned plugin assembly.
Three plug-in assemblies were
supplied with each transmitter, as
only three frequencies were allocated
to each network. The wiring of each
plug-in was such that the correct counterpoise was automatically connected
for the frequency in use. As for the frequencies used, in 1935 the base station
at Wyndham was allocated 1600kHz,
5300kHz and 8830kHz (the broadcast
band only extended to 1500kHz at
that time).
The receiver’s tuning range remained nominally the same as previous models, with enough plug-in
coils to cover from 550kHz to around
10MHz. The higher frequency coils
were wired in such a way that bandspreading was achieved for easier
siliconchip.com.au
tuning, as can be seen in the model
36 circuit diagram.
For those unfamiliar with bandspreading, it is a mechanical or electronic means of spreading the tuning
out across a band, which makes for
easier tuning. A typical dual-wave
receiver tunes from 6-18MHz in one
sweep, which makes it hard to tune
accurately. By contrast, a set with
band-spreading splits that range up
into multiple bands and is therefore
easier to tune accurately – eg, an AWA
7-band set has seven bands which tune
from 550kHz to 22.3MHz.
Once again, I built replica transmitters to check their performance. They
performed pretty much as predicted.
In the model 36 set, the 19 valve is
overloaded and some standing bias
would have been a good idea. I did
not build a replica 36 receiver, as
Graham Pitts, VK6GF – the Base Director at Alice Springs from 1944 to
1953 – assured me that these receivers
performed satisfactorily.
Summary
The early development of the Flying Doctor pedal radios is fascinating.
In this article, I’ve given you but a
glimpse of what happened over the
years from 1912 to 1936. It progressed
from nothing to Morse code transmissions from the out-stations (homesteads) and voice transmission from
the base station at Cloncurry in 1929,
and then to voice transmissions from
the out-stations and the base stations
in 1935/6.
Due to the low power of the outstation pedal radios, the reception at
the base stations was, more often than
not, very poor. By contrast, base station
transmissions were clearly heard most
of the time as the transmitter power
was much greater than the 1.5W output
of the early pedal radios.
In late 1945 (after the end of WW II),
out-station transceivers of up to 20W
became available which improved
communications performance markedly. Depending on the circumstances,
the base transmitter powers varied
between 20W and 400W output when
AM transmissions were at their peak
use.
For those who wish to know a lot
more about the development of communications in the outback, my book
“Outback Radio – from Flynn to Satellites” will be helpful – see adjacent
SC
panel.
siliconchip.com.au
BOOK REVIEW
By Leo Simpson
History of
Outback Radio
Outback Radio, from Flynn to
Satellites, by Rodney Champness.
Published 2004. Soft covers, 210
x 296mm, 186 pages. ISBN 0 646
43674 0. $39.95.
Just by coincidence, this month’s
Vintage Radio column happens to
cover some of the subject material in
this book, involving the pedal radio
developed by Alf Traeger. Rodney
Champness has put a great deal of
research into this book, going as far
as to reproduce some the early radios
to check their performance.
In total, there are 17 chapters
and eight appendices and the story
goes right back to the beginnings
of European settlement. The first
chapter is largely devoted to the
Overland Telegraph which began to
be installed around Australia in the
1850s. In the days before the 1920s,
the Telegraph and the various state
railways represented the only ways
to get messages quickly over vast
distances and those methods left
vast areas of Australia totally isolated. Few people had telephones
and so there was a vast challenge
which was taken up by John Flynn.
John Flynn and Alf Traeger are the
two heroes of this book.
Rodney Champness proceeds to
describe the development of early
radio communications in minute
and exhaustive detail, covering
not only the various transmitters
and receivers but also the innovative pedal generators, designed by
Alf Traeger and Henry Kauper. An
incidental detail is that the pedal
generators designed by Traeger only
supplied the transmitter’s high voltage while the remaining filament
and other supplies were provided
by batteries.
While the main thrust of the
book is the pioneering radio work
to complement the Royal Flying
Doctor Service, a good portion is
devoted to more recent develop-
ments since the 1950s, right up
to the use of satellite communications, EPIRBs and GPS.
The eight appendices are of
particular interest. Appendix one
is a synopsis of the 17 chapters of
the book while appendix two is a
collection of early transmitters and
transceivers and reviews of their
performance. This will probably
be the most closely read section of
the entire book. Appendix three is
a detailed discussion of aerial and
counterpoise systems – critical to
early radio communications.
Appendices four and five are collections of miscellaneous information, significant dates, valve data
and radio frequencies. Appendix
six contains brief profiles of outback radio pioneers and appendix
seven is a comprehensive glossary.
Appendix eight is the bibliography.
In summary, this is a thoroughly
researched history of outback radio
which will be of value to anyone
interested in early Australian radio.
The book is available from the
author, Rodney Champness, 6 Mundoona Court, Mooroopna, Vic 3629.
The price is $39.95 plus $8 postage.
Payment may be made by cheque or
money order. (L. D. S.)
January 2005 89
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