Mercury Wireless station new apparatus
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From The Mercury, 23rd December 1926, page 7
WIRELESS STATION Installation of New Apparatus Range Greatly Increased
The Hobart commercial wireless station was erected in 1912 ctn the Domain as part of a defence
scheme for Australia, and since then has been operating continuously, exchanging traffic between
ships at sea, the Islands round Tasmania and mainland stations. Several times it has proved
useful in cases of ships in distress, and commercially Its value has Increased until now the station
handles anything up to 50 messages a day
lt had been realised for some time that the station had become obsolete with the passage of time,
and attempts have been made to modernise it, and the station has now been up[graded] to the
same standard as the remainder of the coastal stations round Australia controlled by the
Amalgamated Wireless Co. By the Installation of the continuous wave and the interrupted
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installation which will be greatly appreciated by wireless listeners-in is the non-Interference with
their broadcasting programmes Tho old spark transmitter broke through very often, and caused
considerable annoyance.
HISTORY OF STATION.
The history of the Hobart commercial static)n has been uneventful since it was Installed in 1912 by
a wireless engineer who had devised his own wireless system This was Mr. Balsillie, and he had
the contract to establish nearly a dozen stations at the principal coastal outposts in Australia The
stations were designed by the Government to exchange commercial traffic, and to act as a
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taken over by the Australian Navy, and for the first time served the purpose for which it was
originally designed Barbed wire entanglements were put up all round it, and the remains of them
may be seen to-day Exciting stories are told of how sentries stationed on the hill were fired at in
the darkness, and of hciw attempts were made by spies to blow the mast up.
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apparatus was supplied from the city mains with direct current, and a motor generator was used
to convert it to alternating current, which was then supplied to a high tension transformer. The
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The whole of the original apparatus has been discarded except the old aerial and mast. In reality a
completE new station has been Installed, as the old aerial is only used for transmitting, a small
single wire has been fixed half-way up the mast at one end and to a tree at the other, and this
picks up the waves for the receiving set. The old transmitting aerial is of a style in vogue at the
time Mr Balsillie Installed the apparatus, and is like a large umbrella supported in the middle by
the mast This form of aerial is certainly not used by the most up-to-date wireless stations, but it is
quite efflcient enough for any requirements cin a coastal station, and the cost of erecting another
would not be justified at present.
THE RECEIVING SET.
The receiving set is much the same as the conventional type of broadcast receiver lt is mounted
in a cabinet on a large Insulating panel, and employs four valves. Two of these valves amplify the
signals just as they are received, the next detects them, and the last amplifies them after they
have been detected The resultant signals are very loud, and ship stations 1,000 miles away can
often be read with the head phones on the operating table ln order that any combination of valves
can be used, a plugging system is employed, which enables the changes to be made
Immediately The reason for this is that ships and stations close to the receiver do not need so
much amplification as those further away, and some of the valves are cut out to reduce the
amplification,
The single wire aerial used with the receiver is designed to give the set selectivity, and takes the
form of a large T, the lead-in being in the middle The smaller aerial also reduces the
atmospherics, which is a very Important consideration in the summer time, when such
Interference is particularly bad ln Tasmania the single wire receiving aerial is, perhaps, not so
necessary as at some of the tropical stations, but the apparatus which has been installed in all the
coastal stations in Australia is standardised, and for this reason the receiving aerial at a tropical
station like Broome is simHar to that used at Hobart
The transmitter, which is really the most important part of the whole station, is remarkably simple
and can be contrctlled completely from the operator's desk To transmit a message he has simply
tct move several switches and send the message by means of the Morse key at his elbow
Different meter dials on the set shctw him how it is operating, and he can hear the note sent out in
the head receivers which he wears all the time. At the completion of the transmission of a
message he simply turns the switches off, moves another on the receiver, and if the wave length
is correct he is able to listen in to the answering signal from the station to which he has been
transmitting Slight adjustment of the wave length of the receiver is easily made by means of
vernier tuning dials lf it is necessary to alter the wave length of the receiver considerably coils
wound for different wave lengths have to be Inserted in plugs. By this means the receiver will
cover all the wave lengths used commercially lt has a reception range from about 200 to 20,000
metres, and Rugby, which operates near the latter wave length, can be tuned in very loudly
HOW A MESSAGE IS SENT.
When the message is hancled in at the counter of the General Post Office for transmission to a
ship at sea, it is handed to a telegraph operator in the post office, who transmits it by land line
telegraph to the wireless station lt is received there by an c)perator on an ordinary telegraph
souncler, is written dctwn on a form, and forwarded by means of the wireless apparatus to the ship
as soon as communication can be effected When a ship is wanted the station sends out the call
letters of the ship wanted, and if the operator on the ship hears the call he answers it Immediately
and signals that he is ready to take the message lt is sent to him in a series of longs and shorts -
dots and dashes of the Morse code -and he copies it down on a pad of special wireless message
forms and sends it tci the passenger to whom it is addressed lf there were no hitch in getting in
touch with the ship, the message could be, in the hands of the addressee within five minutes of Its
being handed in at the telegraph office.
TECHNICAL DESCRIPTION.
The transmitter is one of the most up-tct-date type which is being Installed in coastal stations for
communicating with ships The power used is in the vicinity of two kilowatts, and the transmitting
range of the station is estimated at about 2,000 miles for all working
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transmitter radiates ln cirder tci alter this wave length, plug sockets and wandering leads are
provided, and tci alter the wave length requires but a momentary alteration of the connections. To
avoid losses the coils are wound on ebonite frames, and consist of very thick bare copper wire.
Several large oil Immersed condensers are also fitted to this unit Oil is a very good insulating
medium, and the immersion in oil insulates the plates of the condensers.
The oscillatctr panel, which makes up the second section of the transmitter, contains the valves,
which are of the Marconi M.T 6 type, each valve being capable of handling 1-2 k w. in its plate
clrcuit.
Thc> whole of the power supply is obtained directly from the supply mains at a voltage of 200 and
50 cycles. Specially designed transformers change the voltage of supply to a suitable valuE for
use in the plate supply and filament circuits, this being 10,000 and 15.5 volts respectively. A fine
adjustment of the voltage is provided for by the use of a variable iron cored choke, Inserted in the
primary of each of the transformers, These chokes are accommodated on the third section of the
transmitter control panel, which is situated within easy reach of the operator.
The high tension transformer has a split secondary winding, with a centre tap, each half being
capable of delivering 10,000 volts. This unsmoothed or raw A.C. voltage is applied to the plates of
the two M.T.6 valves through the two radio frequency chokes, the centre tap being connected to
earth This arrangement permits of full wave self rectification, but no smoothing devices are used.
In order to permit of the transmitted signal being received by a crystal or non oscillating valve
receiver, a variable speed chopperwheel is provided. This is used in conjunction with a special
uncoupling coil. The latter coil is mounted on the same frame and between the aerial inductance
and coupling coil. The function of the uncoupling coil is to preve transfer of energy from the
coupling coil to the aerial This occurs during the periods when t rushes of the chopper motor
are on insulating segments. The coupling and uncoupling coils afe then connected in eries, and
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being wound in opposing directions, no energy is transferred to the aerial. During t period when
the brushes are on cctnducting segments, the uncoupling coil is shctrt circuited and
energy takes place.
Keying can be accomplished either by inserting the key in the coupling-uncoupling coil circuit or in
the pi.imary of power transformer. The latter method is preferable on account of its not being
necessary to carry radio frequency leads to the operating table
[Picture caption]
The interior of Hobart Commercial Radic) Station, showing thct new apparatus Installed recently
The control panel may `--
be seen at the left of the picture and the receiving set ln front of the operator.