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Title & Abstract Description Claims Full Text
(8/ 12)
Physical
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250 volts
(5)
11 drops
(1)
80 percent
(1)
Gene Or Protein
(3/ 3)
WC2
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Fof
(1)
Tne
(1)
Company Reg No.
(2/ 2)
DS 3249
(1)
DS 8972911
(1)
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Number # GB600024A # #
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Title
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Improvements in or relating to radio detecting devices for frequency
modulated signals
Abstract
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[Class 40 (v)] A frequency discriminator comprises means for converting
signals into square pulses of constant amplitude, and spacing inversely
proportional to the frequency, and means for obtaining an audio-frequency
signal of magnitude proportional to the number of pulses produced during an
interval determined by a timing circuit.
The output of the intermediate frequency stages are applied through a
coupling coil 10 and biassing network 12, 13 to the control grid of a
pentode 11, which conducts for a part only of each positive half-cycle of
the intermediate frequency.
The pentode 11 has a sharp cut-off and provides an output composed of
square pulses.
The timing circuit 14 comprises a free-running multivibrator operating
at a fixed frequency and adjusted so that one triode 17 conducts for much
longer periods than the other triode 18.
During the conducting period of the triode 17, the lower plate of
condenser 20 is at a very low potential.
While pentode 11 is driven below cut-off, condenser 21 charges through
the diode 16.
When pentode 11 conducts, the point 23 tends to a negative voltage,
diode 16 ceases to conduct and diode 15 conducts, thus permitting condenser
21 to discharge into condenser 20.
When pentode 11 is again cut-off, condenser 21 recharges, but condense?
20 retains its charge since diode 15 no longer conducts.
Condenser 21 has a capacity many times larger than that of condenser
20, the negative voltage across which increases by a small amount for each
cycle of intermediate frequency, until valve 17 of multivibrator 14 ceases
to conduct, when condenser 20 will be discharged through diodes 15, 16.
The voltage appearing at the point 24 is an audio voltage proportional
to the frequency of the signal, with components of the intermediate and
multivibrator frequencies, which are removed by a filter 25, 26.
The output of the pentode 11 consists of pulses of uneven duration, but
pulses of equal duration may also be used.
Description
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W.=-Xt:FF at
2 and A#b 1 3
PATENT SPECIFICATION 60O,024
Convention Date (United States of America): Oct. 24, 1944. less than
Application Date (in United Kingdom): April 6, 1945. No. 8574j45:
Complete Specification Accepted: March 30, 1948.
(Under Section 6 (I) (a) of the-Patents and c. (Emergency) Act, 1939,
the proviso to Section 91 (4) of the Patents and Designs Acts, 1907 to 1942,
became operative on April 27, 1945.) INDEX AT ACCEPTANCE:-Class 40 (v),
L18j.
COMPLETE SPECIFICATION
Improvements in or relating to Radio Detecting Modulated Signals
Devices for Frequency ERRATUM SPECIFICATION NO. 6COO24
In the heading on page 1 de lete ' (Under Section d (i) (a) of the
Patents and c. (Dnergency) Adt, 1939 the proviso to Section 91 (4) of the
Patents and Designs Acts, 1907 to 1942 became operative on April 27, 1945nU.
THE PATENT OFFICE, 18th Varch, 194,9.
DS 8972911 / 3249 160 3/49 R The present circuit operates to count the
number of cycles of intermediate frequency, frequency modulated, signals
occurring in a fixed time interval and derives from this counted number a
signal which is similar to the modulated signal at the transmitter.
It is an object of the present invention to provide a detector of
frequency modulated signals which shall be insensitive to amplitude
modulated signals and which requires no balancing or the like.
It is a further object of the invention to provide such a detector
which operates by counting the number of cycles of I[[F]] frequency
modulated signals occurring during a fixed time interval.
It is a further object of the invention to provide such an FM detector
which is simple and inexpensive to construct and is stable in operation.
According to the invention there is provided a detector of frequency
modulated signals comprising means for converting said signals into
square-topped signals of constant amplitude and of spacing inversely
proportional to the frequency of the frequency modulated signals, and means
for applying said square-topped signals and a signal from a timing signal
source to an output circuit for producing therein a signal having an audio
frequency component of magnitude proportional to the -number of
square-topped [Price 1/-] circuit of the ff1V detector ot tne invention;
Figure 2 is a curve showing the voltage 70 applied to the detector plotted
as a function of time; and Figure 3 is a curve showing the output of the
detector as well as the derived audio signal both plotted as a function of
time. 75 Referring now to the drawings, the intermediate frequency signal
from the last intermediate amplifier is applied to the control grid of the
pentode 11 through the coupling coil 10 and associated circuit elements. The
80 pentode 11 has a sharp cut-off characteristic.
The resistance of resistor 13 is high and the time constant of the
condenser resistance combination 12-13 is long compared to the period of one
cycle of the intermediate 85 frequency so that the average value of the bias
developed across the resistor 13 and applied to the pentode 11 is equal to
the peakto-peak amplitude of the intermediate frequency carrier wave applied
to the grid 90 circuit of pentode 11. Consequently, if the peak-to-peak
amplitude of the intermediate frequency signal is greater than the cut-off
bias of the tube the pentode conducts during a portion only of the positive
half of the 95 intermediate frequency cycle. As a consequence, the output
from the pentode is represented by Figure 2 and is a wave which is square
topped and the amplitude of which is constant. 100 9 9A. d1 2-99WI b PATENT
SPECIFICATION 6(
CAR a_ _+/1 1- - - A:__ C. A--- -n- A E Convenuon Date (united C tates
oT -merica): OUct.
Application Date (in United Kingdom): April 6, 19, \ j l S B M 7
Complete Specification Accepted: March 30, 1948.
C __ '| '| (Under Section 6 (1) (a) of the-Patents and c. (Emergej o u
Ra/D proviso to Section 91 (4) of the Patents and Dew 1942, became operative
on April 27, 1945.) Lq, g V44. t5. No. 8574/45. icy) Act, 1939, the signs
Acts, 1907 to INDEX AT ACCEPTANCE:-Class 40 (v), L18j.
- COMPLETE SPECIFICATION
Inprovements in or relating to Radio Detecting Devices for Frequency
Modulated Signals We, PILco RADIO AND TELEVISION CoRPoRATioN, a corporation
organized under the laws of the State of Delaware, United States of America,
of Tioga and C. Streets, Philadelphia, State of Pennsylvania, United States
of America, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and
ascertained in and bythe following statement:-
The present invention relates to radio apparatus and particularly to a
detector of frequency modulated signals.
More particularly still the invention provides a detector of frequency
modulated signals which is insensitive to amplitude modulated signals and
does not require balancing, limiting or the like.
The present circuit operates to count the number of cycles of
intermediate frequency, frequency modulated, signals occurring in a fixed
time interval and derives from this counted number a signal which is similar
to the modulated signal at the transmitter.
It is an object of the present invention to provide a detector of
frequency modulated signals which shall be insensitive to amplitude
modulated signals and which requires no balancing or the like.
It is a further object of the invention to provide such a detector
which operates by counting the number of cycles of I[[F]] frdquency
modulated signals occurring during a fixed time interval.
It is a further object of the invention to provide such an FM detector
which is simple and inexpensive to construct and is stable in operation.
According to the invention there is provided a detector of frequency
modulated signals comprising means for converting said signals into
square-topped signals of constant amplitude and of spacing inversely
proportional to the frequency of the frequency modulated signals, and means
for applying said square-topped-signals and a signal from a timing signal
source to an output circuit for producing therein a signal having an audio
frequency component of magnitude proportional to the number of square-topped
[Price 1/-] impulses produced during each interval as determined by said
source of timing signals.
There is also provided a detector of the above type including means to
charge a capacity upon each increase in voltage of said 55 square-topped
impulses, a second capacity connected to said electronic switching means,
means to discharge said first mentioned capacity into said second mentioned
capacity upon each decrease in voltage of said squaretopped wave, and means
to discharge said second mentioned capacity upon the completion of each time
interval.
Other objects and features of the invention will be apparent when the
following description is considered in connection with the annexed drawings
in which:Figure 1 is a schematic diagram of the circuit of the FM detector
of the invention; Figure 2 is a curve showing the voltage 70 applied to the
detector plotted as a function of time; and Figure 3 is a curve showing the
output of the detector v- well as the derived audio signal both plotted as a
function of time. 75 Referring now to the drawings, the intermediate
frequency signal from the last intermediate amplifier is applied to the
control grid of the pentode 11 through the coupling coil 10 and associated
circuit elements. The 80 pentode 11 has a sharp cut-off characteristic.
The resistance of resistor 13 is high and the time constant of the
condenser resistance combination 12-13 is long compared to the period of one
cycle of the intermediate 85 frequency so that the average value of the bias
developed across the resistor 13 and applied to the pentode 11 is equal to
the peakto-peak amplitude of the intermediate frequency carrier wave applied
to the grid 90 circuit of pentode 11. Consequently, if the peak-to-peak
amplitude of the intermediate frequency signal is greater than the cut-off
bias of the tube the pentode conducts during a portion only of the positive
half of the 95 intermediate frequency cycle. As a consequence, the output
from the pentode is represented by Figure 2 and is a wave which is square
topped and the amplitude of which is constant. 100)O,024 -1 600,024 As shown
in Figure 2 the square topped wave is composed of pulses of unequal duration
and of uneven spacing, since, with the system described above both the
duration of the pulses and the spacing between would vary. It should,
however, be understood that a wave having impulses of equal duration can
readily be produced by known methods and that therefore the curve of Figure
2 represents but one wave form of output from the pentode which is useful in
the detector of the invention.
The detector of the invention comprises a multi-vibrator generally
designated as 14 together with the diode rectifiers 15 and 16, and the
various associated circuit arrangements about to be described. The
multivibrator comprises two triodes 17 and 18 together with proper
interconnections which are well known in the art. The multivibrator has a
fixed frequency, for example, 25KC, and is preferable adjusted so that
triode 17 is in the conducting condition for longer periods than in the
non-conducting condition, e[[g]], for 80 percent , or more, of the operating
cycle.
The details of the circuit can best be described byconsideringthe
operation thereof.
Let it first be assumed that the tube 17, that is, the right-hand
triode of the multivibrator as seen in Figure 1, is conducting, then the
plate of tube 17 and consequently the lower plate of condenser 20 will be
substantially at ground potential. With this condition in mind, it will be
seen that, while the plate voltage of the pentode 11 is 250 volts , that is
while the pentode 11 is driven below plate current cut-off value, the
condenser 21 charges to 250 volts through the diode 16. When the plate
voltage of pentode 11 drops to approximately zero, the point designated 23
tends to go to a minus 250 volts . Under these circumstances, tube 16 ceases
to conduct but tube 15 becomes conductive and consequently, condenser 21
discharges into condenser 20 through the tube 15.
If the condenser 20 has a capacity many times (for example, 2500 times)
that of condenser 21, then a small portion, in this case approximately
1/2500 of the total voltage of 1/10 of a volt will appear across condenser
20, the upper plate being negative with respect to the lower plate.
When the plate of pentode 11 again has 250 volts thereon condenser 21
is recharged.
However, condenser 20 cannot discharge because tube 15 is
non-conductive during this interval. Then for each positive cycle of
intermediate frequency the negative voltage across condenser 20 is increased
by a definite amount which in the example heretofore given is 1/10 of a
volt.
When the right-hand section, that is tube 17, of the multivibrator 14,
goes out of conduction the voltage at the plate thereof rises to plus 250
volts . The voltage at the point 24 tends to follow, but is prevented from
going above approximately ground potential by reason of the connection of
the 70 two diodes 15 and 16.
Thus the voltage occurring between the point designated 24 and ground
will be as shown in Figure 3, and the higher the intermediate frequency the
greater the number of 75 pulses which will be counted during the given time
interval, t, and consequently, the greater the amplitude of the voltage at
point 24. For example, if the intermediate frequency varies from 4.225 MC to
4-375 MC, 80 the number of pulses counted during each KC interval, or each
1/25000th of a second, will vary from 169 to 175.0. Clearly then the voltage
appearing at the point 24 is an audio voltage proportional to the frequency
of the 85 signal, with intermediate frequency and 25 KC components. However,
the use of the filter comprising the coil 25 and condenser 26 serves to
remove all but the audio components and therefore an audio wave, as
indicated by 90 the (lash line of Figure 3, results.
It will, of course, be understood that both the intermediate frequency
and the multivibrator frequency may be iaried between wide limits but bust
always he in substantial 95 excess of the upper limit of audibility.
While a preferred embodiment of the invention has been described it
will be clear that the principle thereof may be utilised in other circuit
arrangements and the values 100 of the circuit elements may be varied
without departing from scope of the invention.
Having now particularly described and ascertained the nature of our
said invention and in what manner the same is to be per-
Claims
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formed, we declare that what we claim is:-
1. A detector of frequency modulated signals comprising means for
converting said signals into square-topped signals of constant amplitude and
of spacing inversely 110 proportional to the frequency of the frequency
modulated signals, and means for applying said square-topped signals and a
signal from a timing signal source to an output circuit for producing
therein a signal having an 115 audio frequency component of magnitude
proportional to the number of square-topped impulses produced during each
interval as determined by said source of timing signals.
2. A detector according to claim 1, wherein 120 said source of timing
signals comprises a multivibrator the two sections of which are alternately
rendered conducting, said alternation occurring at a. predetermined rate,
and said signal having an audio frequency component of a magnitude
proportional to the number of impulses produced during the interval of
conduction of one of said multivibrator sections.
3. A detector according to claim 2, wherein 130 600,024 a capacity is
charged upon each increase in voltage of paid square-topped impulses, and
another capacity is connected to the plate of one of a pair of triodes
comprising said multivibrator, and means are provided to discharge said
first mentioned capacity into said second mentioned capacity upon each
decrease in voltage of said square-topped wave and means are provided to
discharge said second mentioned capacity when the second triode becomes
conductive.
4. A detector according to claim 3, wherein said means for converting
the signals to square-topped form comprise a pentode tube having a sharp
cut-off characteristic, and means to apply the frequency modulated signals
to the control grid of said pentode, said first capacity being connected to
the plate circuit of said pentode and being charged to the plate voltage of
said pentode when said pentode is driven below cut off, said second capacity
being connected to the plate of one of said multivibrator tubes and means
being provided for discharging said first mentioned capacity into said
second mentioned capacity when said pentode conducts whereby the charge of
said second capacity is increased by equal increments upon the reception of
each cycle of frequency modulated signal and means being provided for
discharging said second mentioned capacity upon the other of said
multivibrator tubes becoming conducting whereby signals are produced having
an audio component proportional to the number of cycles of frequency
modulated signal received during a predetermined time interval.
5. A detector according to claim 3 or 4 including a pair of
oppositely-poled rectifiers, one of which forms a portion of the charging
circuit fof said first mentioned capacity and the other of which forms a
portion of a circuit for discharging said first mentioned capacity into said
second mentioned capacity when said pentode conducts whereby the charge of
said second capacity is increased by an equal increment upon the reception
of each cycle of frequency modulated signal.
6. A detector according to claim 3, 4 or 5, including means for
supplying the audio frequency components of the signals formed by said
charging and discharging of said second mentioned capacity to an output
circuit.
7. A detector according to claim 6, having an inductance and capacity
for supplying 55 the audio frequency components of the signals formed by
said charging and discharging of said second mentioned capacity to the
output circuit.
8. A detector for frequency modulated 60 signals, comprising means for
converting said signals into square-topped signals of constant amplitude and
of spacing inversely proportional to the frequency of the frequency
modulated signals, electronic switching means 65 including means to render a
circuit alternately conducting and non-conducting, and means for producing a
signal having an audio frequency component of magnitude proportional to, the
number of square-topped 70 impulses produced during each conductive interval
determined by said electronic switching means.
9. A detector according to claim 8, including means to charge a
capacity upon each 75 increase in voltage of said square-topped impulses, a
second capacity connected to said electronic switching means, means to
discharge said first mentioned capacity into said second mentioned capacity
upon each 80 decrease in voltage of said square-topped wave, and means to
discharge said second mentioned capacity upon the completion of each time
interval.
10. A detector of frequency modulated 85 signals substantially as
hereinbefore described and as illustrated in the accompanying drawings.
Dated this 6th day of April, 1945. For PHILco RADIO AND TELEVISION
CORPORATION. STEVENS, LANGNER, PARRY and ROLLINSON, Chartered Patent Agents
5-9 Quality Court, Chancery Lane, London, W[[C]]2. and at East 41st Street,
New York 17 New York, U[[S]]A. Printed for His Majesty's Stationery Offlce,
by Chorley and Pickersgill Ltd, Leeds - 39-222- 1948 Published at The Patent
Office, 25 Southampton Buildings, London WC2 , from which copies, price Is
Od each (inland) is Id (abroad), may be obtained.
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