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NOV- 19, 1946-
P. E. A. cOwLEY ET AL
2,411,415
TELEGOMMUNICATION SYSTEM
Filed Dec. 3, 1945
Low PAss FILTER
I
I
Low PAss FILTER
11
-— ALP 1
I
-1--
'
DIREcTIONALcARRIER 5 P1
ALP 2
5P 2
FILTER & AMPLIFIER \
DIREcTIONAL CARRIER
-* FILTER & cONTROL
'
‘—>7—
10
——
AMPLIFIER
51
S2
l‘
1
BAND-PASS RECEIVING
-
'
12
BAND-PAss RECEIVING
FILTERs
FILTERs
OscILLATOR- Po
.
PRF
/ PILOT RECEIVING
‘
FILTER
SENDING END
PA
PILOT FREQUENCY
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-
F1
1
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-
PLI
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AMPLIFIER
PILOT
FREQUENCY
LEvEL INDICATING
EQUIPMENT
RECEIVING END
PI
F1? 2
By
F’:
COWZey a‘rzzZ
E: 6. W3 25
Patented Nov. 19, 1946
2,411Ai5
UNITED STATES PATENT ornca
2,411,415
TELECOMMUNICATION SYSTEM
Percy Edward Alexander Cowley, Coventry, and
Eric Cliiford Walls, Liverpool, England, assign
ors to Automatic Telephone & Electric Com
pany Limited, Liverpool, England, a British
company
Application December 3, 1943, Serial No. 512,816
In Great Britain January 20, 1943
4 Claims.
(Cl. 178—44)
1
2
The present invention relates to telecommuni
cation systems particularly those employing car
rier current, and ?nds advantageous applica
coei?cient of the ?lter for the pilot frequency
compared with that of the ?lter for the main
channel is counteracted by ‘including in the pilot
frequency receiving circuit an ampli?er arranged
tion to systems in which, for gain control pur
to have a positive gain/temperature coe?icient.
The invention will be better understood from
the following description of one method of car
nalling frequencies and has a frequency value
rying it into effect which should be taken in
of the same order thereof. The chief object of
conjunction with the accompanying drawing
the invention is to minimise the adverse effect
of ambient temperature variation on the char 10 comprising Figs. 1 and 2. Fig. 1 shows in block
schematic form speech side-band and pilot fre
acteristics of the ?lters employed which in the
quency transmitting and receiving arrangements
particular application referred to may upset the
in a typical multi-channel carrier telecommuni
control function of the pilot frequency.
cation system using single side-band speech
In such systems the pilot frequency in follow
transmission and employing different channels
ing the same course or path as the carrier fre
for transmission in each direction over an ordi
quencies is subjected to the same transmission
poses, a pilot frequency is transmitted over the
same medium as the carrier speech and/or sig
loss. Thus any common apparatus such as line
or directional ?lters in said path may have a
nary telephone line also used foraudio frequency
transmission. Fig. 2 shows circuits of a one-‘
valve temperature-compensated pilot frequency
transmission loss which varies with ambient
temperature Without affecting the relative re 20 ampli?er of the negative feedback type, the feed
back circuit incorporating resistance elements
ceived levels of the pilot and carrier frequencies.
having different temperature co-e?icients.
At the receiving end, where ?lters are employed
Referring 'now to Fig. 1, It represents an
to separate the pilot from the carrier frequencies,
audio-frequency telephone line on which a multi
it is essential for satisfactory operation that the
?lters individual to said carrier and pilot fre 25 channel carrier system is superimposed. At the
quencies shall have equal loss/temperature co
sending and receiving ends SE and RE‘, there are
inserted the audio frequency low-pass ?lters
efficients,- that is to say, that the respective
ALPI and ALPZ which serve to exclude the car
losses with increase in temperature shall either
rier and pilot frequencies‘from the sending and
remain constant or shall increaseto an equal
receiving audio frequency‘ telephone apparatus.
extent.
At the sending end SE, carrier frequency speech
It is found that the band pass carrier re
ceiving ?lters have substantially zero loss/tem
perature co-ef?cients, but the pilot receiving
is fed to one of a number of leads such as 10
?lter has, due to its highly selective nature a
from the modulating equipments, not shown,
while the pilot frequency is generated byfthe
considerable positive loss/temperature co-ef?
cient. The invention provides a simple method
.pilot and speech side~band frequencies is desig
oscillator P0.
The equipment common to the
of compensation whereby a substantially zero
loss/temperature co-ef?cient can be obtained for
nated SPI and includes the directionai carrier
the pilot frequency receiving equipment.
equipmentindividual to the speech side-‘bands ,
?lter together with amplifying équipment. The
is designated SI and includes the bandpass sin
gle side-band sending ?lters.
At the receiving end RE, SP2 designates the
equipment common to the pilot frequencies and
temperature, a compensating arrangement is
‘speech side-bands and includes the directional
provided in which an ampli?er employed in con
junction with a ?lter circuit is arranged to have 45 carrier ?lter together with a control ampli?er
whichis normally set to provide a zero overall
a positive gain/temperature coefficient of such
gain, but the gain of which'is adjustable in ac
value as to compensate substantially completely‘
According to one feature of the invention, in
a telecommunication system employing ?lter cir
cuits the attenuating effect of which varies with
for the positive loss/temperature coefficient of
' cordance with the received pilot frequency level.
The equipment individual to the speech side
According to another feature of the invention, 50 bands is designated S2 and includes band-pass
receiving ?lters via which the received side
in a telecommunication system employing a pilot
the ?lter.
.
' frequency transmitted over the main communi
cation channel for the purpose of gain control,
a compensating arrangement is provided in
bands are directed over a lead such as: IE to their
appropriate receiving demodulators. The highly
selective pilot receiving ?lter is designated PRF,
Which the effect of the greater loss/temperature 55 the succeeding pilot frequency ampli?er is desig
2,411,415
3
4
hated PA, whileyPLl represents pilot frequency
that there will be a corresponding slight overall
positive loss/temperature co-e?cient for the pilot
level indicating equipment by means of which the
gain of the common control ampli?er in equip
ment SP2 can be manually or automatically ad
justed in accordance with the received pilot fre
quency level. The positive loss/temperature co
ef?cient of the pilot receiving?lter PRF is con
siderable owing particularly to the nature of this
?lter, while that of the band-pass speech side
band receiving ?lters S2 is substantially zero.
In order to match the loss/temperature charac
vreceiving equipment.
It will be understood that the invention is not -
limited to the particular method shown of pro
ducing the required ampli?er gain/temperature
characteristic.
,
‘
' What we claim as new and desire to secure by
Letters Patent is:
1. In a telecommunication system, a compen
sating arrangement comprising in combination
a communication channel, a pilot frequency oscil
teristics of the pilot frequency receiving equip
lator connected to one end of said channel, a ?lter
ment with that of the speech side-band receiving
circuit having a positive loss/temperature co
equipment, it is arranged that the pilot fre
quency ampli?er PA is given a positive gain/tem~ 15 e?icient, said ?lter‘ circuit being sharply tuned
to the-‘frequency of said pilot frequency'oscillator
perature co-e?icient which will compensatejfor.
and connectedto the other end of said channel,
the positive loss/temperature co-e?icient of the
an ampli?er for amplifying said pilot frequency
preceding pilot receiving ?lter PRF.
‘
"
after its passage through said ?lter, temperature
One suitable form of temperature-compensated
responsive means in said ampli?er, means con
ampli?er is shown in Fig. 2 where leads l3 and ill
trolled by said temperature-responsive means for
extend from the pilot receiving ?lter and the out
automatically altering the gain of said ampli?er
put leads I5 and I6 extend to the pilot level in
so as to compensate for the increased loss in said
dicator. The grid of valve V automatically re
ceives a standing negative bias by virtue of the
biassing resistance RI
?lter with increase of temperature, and an in
dicator connected to the output of said ampli?er
'
and
its associated by- ‘
for indicating the level of said pilot frequency.
pass condenser Ci, while one of the two secondary
windings of the output transformer T2 is centre
tapped and is connected up with two resistance
2. In a telecommunication system, a com
pensating arrangement comprising in combina
tion a communication channel, a pilot frequency
elements R and S so as to form a bridge network,
across the centre points of which a feedback cir-' 30 oscillator connected. to one end of said channel,
a, ?lter circuit having a positive loss/temperature
cuit is taken via the secondary winding of input
transformer TI to the valve grid.
coe?'lcient, said ?lter circut being sharply tuned
Resistance
. to the frequency of said pilot frequency oscillator
‘ and connected to the other end of said channel,
ture co-e?icient, while resistance element S‘ 35 an ampli?er including a thermionic valve with
element R is made up of one of theknown forms of
copper/nickel alloy which has a zero tempera
.utilises iron wire which has a considerable posi
tive temperature co-e?icient.
At some temperature which is preferably well
above that to which the apparatus will be sub
jected, the bridge is arranged to be balanced and‘
resistances R and S are convenientlyrarranged
negative feedback for amplifying said pilot fre
quency after its passage through said ?lter, tem
40
via the feedback path. At the highest expected,
ambient temperature, the static resistance R may ‘ ‘
S falls to a value of the order of 15,000 ohms with
‘ the result that the feedback is made’ negative.
With further decrease in temperature ‘the re
sistance S lowers correspondingly, thus ‘increas
ing the negative feedback and so decreasing the
gain of valve V. By the choice of suitable values
for'resistances R and S the gain/temperature
characteristic of the ampli?er can be adjusted to
give the required performance.
'
It may be that certain band-pass receiving
?lters have a, small positive loss/temperature
characteristic in which case the compensation in
the pilot frequency ampli?er will be made such
feedback to said valve so that with increase of
temperature the increase of gain of said‘ ampli?er
compensates for the increased loss in said ?lter.
3. A compensating arrangement in accordance
to have values of the order of 20,000 ohms each.
There is then zero feedback from anode to grid
maintain its 20,000 ohm valueywhile resistance
perature-responsive means in said ampli?er, and
means controlled by said temperature responsive
means for automatically altering the amount of
with claim 2 in which the sense and amount
of the feedback is controlled by a bridge arrange
ment employing two resistances composed respec
tively of materials having appreciably different
resistance/temperature coefficients.
50
4. A compensating arrangement in accordance
with claim 2 in which the sense and amount of
the feedback is controlled by abridge arrange-p
‘ ment employing two resistances, one resistance
being composed of a copper-nickel alloy having
a substantially zero temperature coef?cient and
the other resistance being composed of iron wire
having a high positive temperature coe?icient."
PERCY EDV/‘ARD ALEXANDER COWLEY.
ERIC CLIFFORD WALLS.
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