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THE "BUZZER"
TELEPHONE.
AN INTERESTING PAPER.
At a recent meeting of the South Australian
Electrical Society an interesting
paper on the subject of the "buzzer" or
condenser" telephone system was read by
Mr. L. H. Griffiths, assistant engineer
electrical engineers branch of the Post and
Telegraph Department.
Mr. Griffiths said that simultaneous telephony
and telegraphy had been a known
quantity for many years, but the general
public use of the system in these States was
of somewhat recent date. One would
imagine from casually reading reports in
the daily papers that all one had to do in
introducing a condenser system was to jog
along to the nearest post-office, hitch on
to the nearest wire, and immediately speak
to almost any locality. Such was not the
case, for There were many things to be considered
before successful condenser telephone
working could be obtained. The
system had its fixed limits, and should
never be expected to work with the same
amount of success as a separately installed
telephone service. One of the greatest
obstacles to successful condenser telephone
working in South Australia was the fact
that the great majority of lines which could
be utilised for the purpose ran parallel for
many miles to heavy battered double current
duplex and quadruplex telegraph circuits.
These big telegraph circuits just about
"bossed the track." If there were a number
of Morse circuits running parallel to each
other on the same line of posts, and amongst
these Morse circuits a telephone circuit,
when any of the keys of the Morse lines
were worked, the effect on the parallel telephone
circuit was that at every action of the
Morse key two distinct clocks were heard,
one click at the beginning and one at the
ending of each movement of the key. If
the whole of the Morse circuits on the line
of posts in question were working at the
same time, it could be imagined that a
great collection of noises would make themselves
manifest in the telephone circuit,
blurring and otherwise spoiling the clear
transmission of speech. The only means of
minimising this trouble would be to tone
down by means of impedance coils, etc,
these big noisy lines, but does
this to any " really effective degree
would mean tinkering with the
fast working efficiency of some of the most
important inter-State double current
Morse lines, and this, of course, was out
of the question. Many were the methods
suggested for overcoming the trouble of
inductive interference from neighboring
telegraph wires, but none appeared to offer
much hope for the practical solution of the
trouble. A comparatively recent idea
was the Adams-Randall high-power transmitted
together with a telephone receiver
whose diaphragm was gradually moved
away from the safe piece until the noises
due to telegraph induction finally disappeared.
The transmitter was made up of
a number of electrodes arranged in multiple,
each electrode being supplied with
a separate battery. The current varia-
tions set up in each primary circuit acted
separately on the secondary circuit, the idea
being to increase the intensity of the transmitting
apparatus, so as to make speech
in the desensitised receiver quite clear. A
little reflection would show, however, that
although such an arrangement when worked
on a special circuit would probably be of
great service, the same arrangement would
be useless when connected to an ordinary
standard telephone system. In spite of
many drawbacks there was no doubt that
the condenser telephone system had come
to stay, and wherever a telephone could be
granted to a comparatively quiet Horse circuit
there would be but little difficulty in
securing a fairly good working service at
a reasonably small cost. It would, however,
be unfair to expect too much from
these superadded circuits. They should in
a large measure act as feelers, a reasonably
cheap means of deciding whether certain
localities were likely to use the telephone
service sufficiently to make it worth
while extending the ordinary trunk line
services to such localities. With the extension
of the ordinary trunk line service
to distant centres they would naturally
be able further to extend the condenser
systems to localities that were at present
outside the commercial-speaking radius.
Long distance telephony in America meant
the very best, and therefore the most
costly equipment. Special posts away
from all telegraphic inductive in
fluences, Nos. 8 and 10 copper
wires, and these wires transposed in
their relative positions to each other (so as
to neutralise the effects of inductive cross-talk
every mile or less were but a few of
the necessities for the successful working of
long-distance telephony. If they found
in the United States that these expensively
constructed lines were not paying on a telephone
traffic basis, they simply leased out
the two telephone wires as separate single
current Morse units, using the telephone as
a superadded unit. In this way two No.
8 copper Assizes connecting New York
with Chicago were earning nearly £4,000
each per annum, and the company still retained
its telephone service. This company
had therefore an assured income of
over £7,000 quite independent of the telephone
service for which the line was originally
built. Successfully to carry out
simultaneous telephony and telegraphy on
the same wire, it was obviously necessary to
arrange matters so that the telephone currents
did not interfere with the Morse
systems, and that the Morse impulses did
not interfere with the telephone apparatus.
To superimposed a telephone on to a single
current Morse circuits the following apparatus
was necessary. A set of telephones
with buzzer call attachment, an impedance
cod, and one or more condensers. The
"buzzer" calling device was simply an ordinary
induction coil, with the familiar
vibrating contact-breaker, built upon the
same lines as the "penny-in-the-slot''
shocker. The "buzzer" coil took the place
of the generator in the ordinary set of telephones,
and its function was to send out
high frequency secondary current"s to the
line. These currents were received at the
distant end on an ordinary telephone re-
ceiver, to the earpiece of which was fixed
a tin funnel, which added volume to the
sound of the incoming "buzzer" call. The
receiver in this instance therefore took the
place of the call bell in an ordinary set of
telephones. Quite a variety and range of
tone could be obtained by the adjustment
of the spiral spring of the "buzzer" coil,
some of the received calls resembling the
final agonies of a dying basso, whilst another
adjustment sent out sounds
resembling an ancient soprano. These
sounds soon get on one's nerves,
An impedance cod or "graduated" was an
ordinary coil of fine silk-covered copper
wire wound on a bobbin in the familiar way.
In addition to the usual iron core piece
this coil was surrounded or clad with iron.
Its function was to tone down or graduate
the Morse impulses, so that they might not
pass abrupt y into the superimposed telephone
receiver. Although impedance coils
allowed a somewhat ready path to the slow
Morse impulses, they had, a distinctly
choking back effect on currents of high
frequencies such as those transmitted by
the telephone. The result was that the
undulatory telephone currents were driven
into their proper channel, and did not waste
themselves over the Morse section of the
circuits. Impedance codes were therefore
opaque to telephonic currents, but transparent
to the slower Morse impulses. A
condenser was made up from' a number of
sheets of tinfoil, each sheet being separated
from the other by means of paraffine
paper or other insulating material. A con-
denser was transparent to telephonic high
frequency impulses, but opaque to ordinary
Morse impulses. These were the elementary
principles that governed the whole question
of condenser telephone workings. The
success of a system depended largely on a
study of local conditions, the right amount
of impedance, and finally the striking of
the happy medium as far as the
capacity of the speaking condensers was
concerned. These systems could be worked
on either single or double wires in the
case of the single line using the earth as
a return. Electricians had to cope with more
noisy inductive disturbances, but had less
line resistance to overcome, whilst in the
case of the two-wire arrangement they
had about double the resistance to overcome,
but were far less affected by induc-
tive disturbances. A properly cross
connected metallic copper wire system was
the ideal one from an all-round efficiency
point of view, but the cost on long lines
was, in the majority of instances, prohibitive.
To superimposed a Morse circuit on
to an existing metallic telephone circuit no
condensers were required. In such a
case merely properly balanced impedance
coils were necessary. It should not be
forgotten that the present South Australian
condenser telephone systems were all
worked on old No. 8 guage iron wire Morse
circuits. From a purely telephone efficiency
point of view these were poor wires
at any time, but when used on the super-
imposed method the test became still more
severe, and, all things considered, the department
had done well with the lines at
its disposal. All the condenser systems
were carefully protected with lightning ar-
resters, and "cut-outs" were supplied, so as
to allow of all apparatus being immediately
disconnected during bad weather, and at the
close of work each evening. Lightning was
the one great weakness of the condenser.
Fully 98 per cent, of the total breakdowns
on condenser systems were due to lightning
piercing the tinfoil sheets, and this
shunting the Morse circuits to earth.
Yet he had known a customer to growl
and condemn the systems because he was
not permitted to speak over a condenser
line during a heavy thunderstorm. Strong,
clear speaking was absolutely necessary over
all condenser systems. Careless speaking
simply meant poor transmission, and the
systems were condemned by those who appeared
too tired to speak close to the transmitter
in a clear even tone. In speaking
over any telephone line it was a good plan
to regulate the distance of the mouth from
the transmitter, so that when speaking the
sound of one's own voice came back to
the ear, via the receiver in a full, strong
tone. Unless one heard this it was a sure
sign that the transmission of the voice was
poor. Perhaps the weakest point of the
condenser system was the means used for
calling up the various stations. This was
known as the "buzzer," and the trouble
was not that the "buzzer'.' failed to call the
station wanted-it did that as a
rule readily enough but in doing so
it created a most pronounced disturbing
influence in neighboring wires, and it sometimes
became a question of waiting until
the "buzzer" was silent before people using
neighboring wires could get on with their
conversations. In America the calling, or
"ordering up," was often done by the
various exchanges on the Morse, such
Morse circuits passing through or being
looped into the exchange. It spoke well
for American management if such an arrangement
could be carried out without delay
to either service. It would be well to
impress on all who used condenser telephones
the absolute necessity of reducing
the "buzzer" call to the lowest possible
minimum. Condenser telephones were
daily on the increase, and the sooner some
better means of calling could be thought
out the better it would be.
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