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Патент USA US2411494

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Nov. 19, 1946.
w. H. BLISS
`2,411,494
RADIO RECEIVER
Filed Aug. 18, 1942
mvENToR
-
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/Lovm/
ArroRNEY
Patented Nov. 19, 1946
2,411,494
UNITED STATES- PATENT GFFICE
2,411,494 -
RADIO RECEIVER
Warren H. Bliss, Orono, Maine, assigner to Radio
Corporation of America, a corporation of Dela
Ware
Application August 18, 1942, Serial No. 455,187
26 Claims.
(Cl. Z50-_20)
2
This disclosure relates broadly to apparatus for
scanning a given frequency band of the radio
spectrum, locating any new signal which appears
The relative speeds of rotation of the condenser
3 and tape 6 must be such that the loop of tape
6 makes one complete circuit while the condenser
therein and controlling a device for making a
3 sweeps through a complete cycle of operation
record of such a signal.
twice. During each cycle of _operation of con
In monitoring the radio spectrum for enemy
denser 3, the receiver 2 will sweep through the
and illegal stations, a transmitter which sudden
desired portion of the radio spectrum to be
ly goes into action sends a short message at high
studied and will be ready for the next sweep.
speed and then shuts down quickly is very hard
The detected output from the receiver 2 is fed
to detect. A primary object of the present inven
through leads 41 and audio transformer 9 into a
tion is to provide a method of and apparatus for
pulse reshaper consisting of gas triodes I2 and
detecting the signals from such unknown sta
I5, sometimes known as “Thyratronsf’ This
tions.
pulse reshaper I2, I5 is sometimes referred to as
An important feature of the present invention
a trigger circuit which requires an initiating pulse
lies in an arrangement which enables the receiver 15 to change the condition of equilibrium for a dura
to scan or hunt continuously over a given band
tion depending in part upon the constants of the
of frequencies, and when a new signal is found
circuit elements and in part upon the electrode
voltages.
,
that was not there previously the receiver stops
hunting and remains on the frequency of the new
The term “reshaper” has here been employed
signal so that it may be recorded. In order to
because the circuit I2, I5 converts the shape of
accomplish this result, a panoramic representa
an initiating pulse into a substantially rectan
tion of all signals in the band is set up, registered
gular pulse for use by the recorder coil in a man
or stored for reference or comparison purposes.
ner described later.
This registration may employ any suitable re
These triodes I2 and I5 have plate resistors II
cording system such as a magnetic tape. The in 25 and I4 and cathode resistors i6 and I9. A mag
coming signals are then continuously compared
netic recording coil -I is connected in series with
with those registered on the tape. The sudden
the cathode resistor I5 of triode I2. Normally,
appearance of any new signal is quickly detected,
that is, in the absence of an initiating pulse, tube
which action causes it to be recorded in another
I2 is non-conducting and tube I5 is conducting.
apparatus as a continuous record available for 30 An initiating pulse reverses these conditions of
study.
current conduction of these two tubes. The grid
A more detailed description of the invention
of gas triode I2 receives the incoming pulses from
follows in conjunction with a drawing whose
transformer 9 over resistor I0. The grid of triode
single figure illustrates a specific embodiment of
l5 is connected to a supply of negative bias C~
this invention.
35 through a large resistor I8 which is shunted by a
Referring to the drawing, unit 2 is any conven
small condenser I'I. A condenser I3 is connected
tional radio receiver with a motor driven Vernier
between the plates of the two gas triodes, and its
tuning condenser 3 which is connected in parallel
value determines the duration of the reshaped
with the main tuning condenser of the receiver.
pulse.
The motor which drives the condenser 3 is labeled 40 A magnetic pick-up coil 8 is located half way
5. It is preferred that the receiver sweep over
around the tape from the recording coil 'I and is
a desired portion of the radio spectrum, and that
connected to an armature 35 of relay 3l having
it follow a standard saw-tooth variation in
oppositely disposed contacts 36 and 31,- by means
which the forward sweep is very slow compared
of which the coil 8 can be connected either to the
to the return sweep. The main tuning condenser 45 grid of vacuum tube pentode amplifier 45 or to
across which the Vernier 3 is connected may be
the B+ plate supply through resistor 33. Pen
the frequency determining element of a local
tode 40 has the usual resistors and condensers
oscillator in a, superheterodyne receiver, or where
for class “A” operation. Its plate is coupled via
a multi-stage tuned radio frequency receiver is
condenser 28 to the grid of a vacuum tube triode
employed, it is preferred that all tuning con 50 2l. This triode 2| has its plate connected
densers of the different stages vary simultaneous
through connection 46 to the cathode of gas tri
ly by a unicontrol means.
ode I2, and the cathode of tube 2| is coupled
A magnetic clutch 4 is so arranged that the
directly to the control grid of gas triode or
motion of condenser 3 may be suddenly stopped
“Thyratron” 2B. Resistors 23 and 22 are also
at any position in response to energizing current 55 used for the grid and cathode, respectively, of
in the coil of the actuating magnet of the clutch.
vacuum tube 2 I .
The motor 5 also drives a loop 6 of magnetic tape.
Resistors 24 and 2l form a potential divider
2,411,494
d
4
between the B+ lead and ground to maintain a
high negative grid bias on gas triode 2% by ele
vating the cathode potential above ground. The
plate circuit oi’ this tube contains in series the
actuating coil ci relay 3l anda switch 3Q. ln
the absence ci”` energizing current`.through the
windingof relay 3i, contact pairs SZ-dß, 3G, 35,
and Sil, ¿iii will be normally open, while contacts
ing every sweep.
Because each station has a
given frequency, the signals from each station
will always appear at the same position on the
panorama. As the receiver continues to hunt
over therspectrum, each station will have a rep
resentative magnetic pulse on the tape and no
new pulsesl will be recorded, since each incoming
pulse will be applied at a point where it was pre
¿i5-3? will be closed. Contact 32 is connected
viously registered. At this time, switch 30 should
to the magnetizing coil of clutch @i and serves to 10 4be closed. Now, if new signals, of a different fre
complete the circuit of this coil with the B+ lead
quency than those previously registered, suddenly
through a resistor 2S. IThe closure oi contacts
appear in the Vspectrum being scanned, these will
Sii-«555i causes the signal recorder 2d to commence
formy new recorded spots, as will 4be explained
recording. Recorder 25 is connected to the re
later.
ceiver 2 by means of leads ¿il and records't’n'e
In order to compare the panoramic radio
signals from the receiver. This recorder may be
record with the constantly incoming signals, a
any conventional type of device for permanently
pick-up coil B and a comparator device are used.
recording radio signals and operates to record
Since the tape is two sweep cycles in length and
only when contacts Sil-fifi are closed by the ac
recorder1 coil 'l and pick-up f8 are spaced one cycle
tion of relay ë l.
20 apart, the pulses picked up by coil il will be at the
The operation of the system of the invention
same phase as those coming from the receiver
will now be described in greater detail: Switch
through the reshaper or trigger circuit I2, I5.
Sil, whose function is described later, is normally
Triode 2l compares these incoming pulses with
open (as shown). The radio receiver-2 is made
those already recorded on the magnetic tape 6,
to swing its tuning over a given frequency band of 25 since the incoming reshapedy pulses from the
the radio spectrum by means of the small motor
cathode of gas triode I2 are applied to the plate
driven condenser 3 which operates in conjunction
of this triode 2|, while the recorded pulses (as
with the main tuning device of the receiver in
picked up by coil ê and amplified by pentode 40)
such a way as to cause it to scan over the given
are applied to the grid of triode 2l. The pulse
band of the radio frequency spectrum in an ap
from the receiver applied to the plate of tube 2l
proximately _linear manner. At the end of each
must be of opposite polarity to the pulse simulta
sweep, the tuning of the receiver very quickly
neously applied to the grid of tube 2i by the pick
reverts to its original position in preparation for
up coil S through pentode lill. IThis condition can
another sweep, or putting it in other words, the
be assured by properly poling the terminal con
tuning jumps back and starts over again. For
nections of the pick-up coil 8. Since the pulse
purposes of explanation, a sweep cycle of one sec
ond duration may be assumed.
As the receiver
sweeps over a portion of the radio spectrum, each
radio signal encountered will appear as_‘a- pulse
of voltage in the output leads el’.
,
applied to the plate of tube 2i is always positive,
the pulse applied to the grid oi tube 2l should
always be negative and of a Value sufficient to
prevent space current flow through tube 2l.
40 When a new signal suddenly appears in the ob
These pulses are recorded on the‘loop of mag
netic tape 6 which is exactly two- sweep cycles in
length. Due to the fact that pulses from the re
served band, the plate of triode 2i will receive
a reshaped pulse for this new signal but since
it has not been registered previously on the mag
ceiver 2 vary widely in both shape and magnitude,
netic tape the grid of this comparator tube 2i
a reshaper or trigger circuit consisting of gas tri 43 will receive no matching or counterbalancing
odes i2 and lâ is provided. Normally, tube |52 is
negative pulse on its grid. Since the plateand
non-conducting and tube
i5 is conducting.
grid pulses of stations already recognized are of
opposite polarity and cancel each other, the ap-v
plication of a pulse to the plate only of tube 2i
lll, it passes through transformer S and is applied
to the grid of tube l2, thus firing or initiating 50 caused by the appearance of a new signal will
produce a pulse of plate current which flows
conduction in tube i2, as a result of which cur
rent is set up through the recording coil l. When
through cathode resistor 22.
tube i2 starts conducting, it changes the con
This pulse of current in tube 2l, which occurs
dition of charge on condenser i3, thus reducing
only for a new signal, will be passed on as a volt
the voltage on the plate of tube I2 below the arc
age swing to trip or ñre gas triode 23. The firing
sustaining value, as a result of which tube l5
of triode 2t energizes the coil of relay 3l which
ceases conduction momentarily. The tubes l2
quickly closes contacts 25E-¿i3 and Sii-fifi. The
and I5 regain their original status after a time
closure of the former contacts causes magnetic
interval depending upon the value of condensers
clutch ¿l to arrest the motion of auxiliary tuning
i3 and il. ïn this_ manner a comparativelyy 60 condenser 3, thus leaving receiver 2 tuned to the
square pulse of current is obtained from the cath
frequency of the station which has just been
ode of tube »l2 for energizing the recorder coil l
found. The operation of relay 3l by virtue of
for each received pulse, irrespective of its char
the closure of contacts 3e, ¿lil also causes recorder
acter. Thus, all pulses received on the receiver
20 to go into operation and start registering the
When a pulse from the receiver appears in leads
2 irrespective of their shape and magnitude, are
recorded on the tape alike.
Since the magnetic tape 6 is synchronized with
the frequency sweep of the receiver, a panorama
of the radio signals in the chosen band of the
radio frequency spectrum is set up or registered
cn the tape as soon as the tape has made a few
revolutions. In the case of keyed continuous
waveY signals, several sweep cycles may be neces'
sary tc set up the complete panorama because the
signals of a given station will not be present dur
newly found signal.
The operation of relay 3i also opens contacts
37-3‘5 and closes contacts ¿iii-35 to apply direct
current to pick-up coil il for magnetic erasing.
While the registered signals on tape ß are being
erased, the signal recorder 2€? is Vreceiving the
newly found signals. The relay Si remains en
ergized until switch 3Q is opened manually at the
will of the operator after the new signals have
been recorded for a desired interval of time. The
panorama of signals may then be set up again
2,411,494
5
6
on the magnetic tape after which switch 30 can
be reclosed to put the system in readiness for
hunting another new signal.
and adapted to open the link between said motor
and said receiver, means responsive to the de
tected output of said receiver including a trigger
It should be noted that application of pulses
circuit and a. magnetic tape recorder coupled to
to the grid of tube 2| in the absence of voltage Ol said trigger circuit for producing recordings rep
applied to the plate of this same tube will have
resentative of the signals received within said
no effect on the signal recorder 20. Also, gas
spectrum, a permanent recorder, an electron dis
triode 2G is normally biased well below the firing
charge device circuit operative solely by a signal
point (i. e., the critical point at which conduc
received within said spectrum but which does not
`tion starts), but when this tube 25 is triggered by 10 register with the recordings on said tape for op
the pulse from a new signal through the inter
eratively connecting said last recorder to the out
mediary of vacuum tube 2l, it maintains a state
put of said receiver, a relay coupled to said elec
of conduction until it is reset to its normal condi
tron discharge device circuit and operative solely
tion of non-conduction by opening switch 3S.
upon the flow of space current through said de
Relay 3l and magnetic clutch 4 must be high
vice, a pair of contacts for said relay one of which
speed devices so that the hunting or scanning
is connected to the energizing coil of said mag
action of the receiver can be stopped instantly;
netic clutch and the other of which is connected
otherwise the receiver tuning would pass on to a
to a source of potential, whereby operation of said
different frequency than that of the newly found
electron discharge device circuit operates said
station. This stopping action is preferably as 20 relay and causes the energization of said clutch
sured by suitable circuits for compensating or
with a resultant fixation of the receiver response
correcting for undesirable overshooting of the re
ceiver tuning because of mechanical factors. In
order to compensate for the possibility that mag
netic clutch 4 may not be able to arrest the mo
tion of condenser 3 quickly enough, when a new
signal is found, so that the tuning of the re
ceiver will not be swept beyond the frequency
where the new signal is found an additional iixed
condenser lill of suitable value is arranged to be
switched in parallel with the Vernier scanning
condenser 3 at the same instant that the mag
netic clutch Il is energized. The rotation and
design of condenser 3 must be such that its ca
band.
3. In a radio receiving system, means for con
tinually and repeatedly changing the receiver re
spense band over a predetermined portion of the
vradio frequency spectrum, means responsive to
the detected output of said receiver for producing
indications representative of the signals received
within said spectrum, and means operative solely
in response to a new signal received within said
spectrum which does not register with the fre
quency positions corresponding to sa-id iirst indi
cations for producing an indication of another
kind and for stopping movement of the receiver
pacitance varies linearly from its maximum to its ‘
response band.
minimum value during the sweep cycle and then
li. In a radio receiving system, a tuning element
snaps back quickly to its maximum value at the
controlling the receiver response band, a motor
end or the sweep cycle. The value of condenser
having a drive shaft linked to said element for
50 can be set to exactly equal the amount of ca
continually and repeatedly changing the receiver
pacitance overshoot of condenser 3. The use of 40 response band over a predetermined portion of
an additional pair of normally open contacts
the radio frequency spectrum, a magnetic clutch
¿iS-£9 on relay 3l 'will switch in the compensat
between said shaft and said receiver, an output
ing condenser 5i) at the proper instant. Another
circuit for said receiver, a trigger circuit coupled
way of obtaining this compensation is to employ
to said output circuit for converting the shape of
known types of automatic frequency control to fr' a voltage pulseappearing therein to substantially
pull the receiver into exact tuning with the newly
rectangular wave form, a, magnetic tape having
found station when stopped in the vicinity of
a recorder coil in circuit with said trigger circuit
the carrier of the unknown station.
for operation from said rectangular wave form
A disadvantage of this last method of com
pulse, said magnetic tape having such length and
pensation resides in the fact that if the newly
being driven at such- speed that it travels one
found station has a frequency close to a strong
complete revolution for an integralI number of
known station, the receiver might be pulled into
cycles of travel of the tuning element, a pick-up
tuning the known station rather than the newly
coil for said magnetic tape positioned at a prede
found station.
termined location on said tape, a normally inop
What is claimed is:
erative signal recorder also coupled to the output
1. In a radio receiving system, means includ
circuit of said receiver, and a comparator device
ing a motor for continually and repeatedly
in circuit both with said trigger circuit and said
changing the receiver response band over a pre
pick-up and responsive to signal pulses from said
determined portion of the radio frequency spec
rigger circuit which do not register with previous
trum, means responsive to the detected output (il) recordings for rendering said signal recorder op
of said receiver' including a trigger circuit and a
erative and for energizing said magnetic clutch
magnetic tape recorder coupled to said trigger
to disengage said motor drive shaft from said
circuit for producing recordings representative
tuning element.
of the signals received within said spectrum, a
5. A receiving system in accordance with claim
permanent recorder, and an electron discharge 65 4, including a circuit operative in dependence
device circuit operative solely by a signal received
upon the operation of comparator device for cor
within said spectrum but which does not register
recting the tuning of said receiver to assure the
with the recordings on said tape for operatively
stopping of said receiver on the frequency within
connecting said last recorder to the output of
said spectrum which corresponds to that of the
said receiver.
signal causing the operation of said comparator
2. In a radio receiving system, means including
device.
a motor for continually and repeatedly changing
5. In a radio receiving system, means for caus
the receiver response band over a predetermined
ing the receiver to repeatedly scan a predeter
portion of the radio frequency spectrum, a mag
mined portion of the radio frequency spectrum,
netic clutch between said motor and said receiver
means for producing indications representative of
.2,411,494
8
'the signals within said spectrum, and means for
`automatically recording solely those signals with
termined portion of the radio frequency spectrum,
means for producing indications representative of
in said spectrum which were ynot present during
the previous scanning operation.
paring the indications with the indications pro- .
the signals within said spectrum, means for com
'2. In a radio receiving system, an antenna
duced in previous scanning operations, a recorder,
a relay for controlling the operativeness of said
therefor, means for causing the receiver to re
ne ,tedlv scan a predetermined portion of the
recorder and ior controlling said clutch, an elec
radio frequency spectrum, means for producing
tronic circuit for controlling said relay, said elec
indications representative of the signals within
tronic circuit being responsive solely to new sig
said spectrum, a recorder, and circuit means re 10 nals within said spectrum which have not caused
sponsive solely to new signals within said spec
indications during the preceding scanning opera
trum which do not register with the frequency
tions for operating said relay to thereby opera
positions corresponding to said indications for
tively connect said recorder to the output of said
operatively connecting said recorder to the out
receiver and to thereby simultaneously energize
put of said receiver and for simultaneously stop 15 said clutch to stop the scanning of said receiver
_ping the scar-„ning of said receiver approximately
approximately at the frequency position of the
new signals.
at the frequency position of the new signals.
8. The method of operating a radio receiving
ifi. In aradio receiving system having a tuning
system having a circuit for detecting the signals
element, an antenna therefor, means including a
impressed thereon which includes the steps of 20 motor and magnetic clutch between said motor
automatically and cyclically varying the tuning
and a tuning element of said receiving system for
of the receiver over a predetermined range of
causing the receiver to repeatedly scan a prede
frequencies, and utilizing any newly detected
termined portion of the radio frequency spectrum,
means for producing indications representative of
signal received by said receiver in said range
which was not present during an immediately
the signals within said spectrum, means for com
preceding cycle of variation for automatically
paring the indications with the indications pro
stopping said cyclical variation at the point at
duced in previous scanning operations, a recorder,
a relay for controlling the operativeness of said
which. the new signal is detected.
recorder and for controlling said clutch, an elec
The method of operating
radio receiving
system which includes the steps of automatically 30 tronic circuit for controlling said relay, said elec
tronic circuit being responsive solely to new sig
cyclically varying the tuning of the receiver over
l a predeten
nals within said spectrum which have not caused
„ed frequency range, comparing the
indications during the preceding scanning opera
time phase of signals appearing in successive
tions for operating said relay to thereby opera
cycles of variation, detecting any new signal re
tively connect said recorder to the output of said
ceived by said receiver in said range which was
receiver and to thereby simultaneously energize
not present during an immediately preceding
said clutch to stop the scanning of said receiver
cycle ci variation, utilizing the detected new sig
approximately at the frequency position of the
nal to stop
variation in tuning, and automati
new signals, and reactance means also under con
caily recording solely the intelligence conveyed by
40 trol of said relay for assuring that the tuning of
said new signal.
the receiver does not sweep beyond the frequency
l0. The method ci operating a radio receiving
position of the new signals.
`
system which includes the steps of automatically
l5. The method of operating a radio receiving
and cyclically varying the tuning of the receiver
system which includes the steps of repeatedly
over a predetermined frequency range, and uti
scanning a predetermined portion of the radio
lizing any new signal received by said receiver in
said range which was not present during an im
frequency spectrum, causing signals emanating
mediateiy preceding cycle of variation for automatically causing the recording of the new signal
Aand simultaneously stopping the variation of the
from identiñable transmitting stations in said p0r
tion of the spectrum to produce one type of indi
cation in said receiving system, and causing a new
signal in said portion of the spectrum which ema
nates from a newly found transmitting station
receiver at substantially the point at which the
new signal is detected.
’
1l. in a radio receiving system, an antenna
therefor, means' for causing the receiver to re
peatedly >scan a predetermined portion of the
suddenly appearing during the scanning of said
spectrum to produce another type of indication,
and automatically recording solely the new signal
to the exclusion of the other signals emanating
radio frequency spectrumv` means for producing
from the identifiable transmitting stations and
indications representative of the signals within
occurring simultaneously with the new signal.
said spectrum, a recorder, circuit means responsive
solely to new signals within said spectrum which
16. The method ci operating a radio receiving
do not-register with the frequency positions corre
system which includes the steps of uniformly,
sponding to said indications for operatively con 60 automatically and repeatedly scanning a prede
necting said recorder to the output of said receiver
termined portion oi the radio frequency spectrum,
and for simultaneously stopping the scanning of
producing indications representative of the sig
said receiver approximately at the frequency posi
nals Within said spectrum, utilizing a new signal
tion of the new signals, and means for assuring
appearing in said portion of the spectrum which
that the tuning of the receiver does not sweep
was not present during the previous scanning op
beyond the frequency position of the new signals.
eration and for which'there is no corresponding
A system in accordance with claim fl, in
indication to automatically stop the scanning oi
cluding means for assuring the stopping of the re
the receiving system at that position which sub
ceiver tuning at the position corresponding to th
stantially leaves the receiving system tuned tothe
frequency of the newly found signals.
new signal, and automatically recording solely said
i3. In a radio receiving system having a tuning
new signal.
'
element, an antenna therefor, means including a
i7. The method of operatinga radio receiving
motor and a magnetic clutch between said motor
system which includes the steps of automatically
and a tuning element of said receiving system for
and repeatedly scanning a predetermined portion
Vcausing the receiver to repeatedly scan a prede
of theV radio .frequency spectrum, detecting the sig
2,411,494
10
nals appearing in said portion of the spectrum,
device coupled to the output of said trigger cir
cuit, and an electromagnetic relay under control
of said electron discharge device circuit, said re
lay having contacts connected to said signal re
and utilizing a new signal appearing in the spec
trum which was not present during the previous
scanning operation to automatically stop the
scanning of the receiving system at that po-sition
which leaves the receiving system substantially
corder.
23. lin a radio receiving system, a tuning ele
ment for said receiving system, a magnetic clutch,
tuned to the new signal.
18. The method of operating a radio
living
system which includes the steps of automatically
and repeatedly scanning a, predetermined portion
of the radio frequency spectrum, producing indi
cations representative of the signals within said
portion of the spectrum, automatically comparing
the positions of said indications appearing in suc
a motor linked to said tuning element through
said magnetic clutch for continually and repeat
edly changing the receiver response band over a
predetermined portion of the radio frequency
spectrum, means responsive to the detected out
put of
receiver for producing indications rep
resentative of the signals received within said
spectrum and for comparing said indications
with the indications representative of signals re
ceeding scanning operations, and automatically
recording solely a new signal in the spectrum
which was not present during the previous scan
ceived during previous scanning' operations, and
ning operation.
means operative solely in response to a new signal
19. The method of operating a radio receiving'
system which includes the step of automatically
scanning a predetermined portion of the radio
frequency spectrum at a constant and relatively
slow rate, automatically restoring the tuning of
received within said spectrum which has not
caused an indication during the preceding scan
ning operation for energizing said magnetic clutch
to thereby stop movement of said tuning element.
24. In a radio receiving system, a receiver hav
the receiver to its starting condition at a fast
ing a tuning element, an antenna coupled to the
rate immediately after the scanning operation in 25 input of said receiver, means including a motor
order to commence rescanning of the same range
and a magnetic clutch linked to the shaft of the
of frequencies, automatically repeating said scan
motor for moving said tuning element and caus
ning operations, detecting a new signal in the
ing the receiver to repeatedly scan a predeter
spectrum which was not present during the pre
mined portion of the radio frequency spectrum,
vious scanning operation, and utilizing said new
means for producing indications representative
signal to automatically stop the scanning of the
system at the frequency position of the new sig
of the frequency positions of the signals within
said spectrum, a recorder coupled to the output
of said receiver, a relay for controlling the eiîec
tiveness of said recorder and for controlling the
energisation of said clutch, and electronic circuit
nal, and continuously recording the intelligence
conveyed by the new signal.
20. In a radio receiving system having a cir
cuit for detecting the signals impressed thereon,
means responsive solely to a new signal within
said spectrum which has not caused an indica
means for continually and repeatedly changing
the receiver response band over a predetermined
tion during the preceding scanning operation for
portion of the radio frequency spectrum, means
operating said relay to thereby operatively con
responsive to the detected output of said receiver 40 nect said recorder to the output of said receiver
for producing indications representative of the
and to thereby energize said clutch for simulta
signals received within said spectrum, a signal re
neously stopping the movement of said tuning
corder, and means responsive to a new signal
element approximately at the frequency position
received within said spectrum which has not
of the new signal.
25. A frequency spectrum monitoring system
caused an indication during the preceding scan
ning operations for operatively connecting said
recorder to the output of said receiver.
comprising a radio receiver having a tuning ele
ment for tuning said receiver over a band of fre
duencies, means including a motor having a shaft
21. The method of operating a radio receiving
system which includes the steps of repeatedly
linked to said tuning element for periodically and
automatically causing said receiver to scan said
scanning a predetermined portion of the radio
frequency spectrum, causing signals emanating
hand from one end to the other at a rate of the
order of once per second, signal storage means
from identifiable transmitting stations in said
portion of the spectrum to produce one type of
for producing indications representative of the
signals within the band being scanned, an elec
tronic circuit responsive to a new signal received
by said receiver and which does not correspond
in time position to any of said indications for
indication in said receiving system, causing a new
signal in said portion of the spectrum which ema
nates from a newly found transmitting station
suddenly appearing during the scanning of said
spectrum to produce another type of indication,
automatically stopping said motor approximately
at the frequency position in
and utilizing said new signal to stop the scan
ning of the system at approximately the fre
quency position of the new signal.
toring the output of said receiver.
2€. The method of operating a radio receiving
system which includes the steps of automatically
and cyclically varying the tuning of the receiver
22. In a radio receiving system having a circuit
for detecting the signals impressed thereon,
means for continually and repeatedly changing
the receiver response band over a predetermined
spectrum at
60 which said signal appears, and means for moni
“ over a predetermined frequency range, establish
portion of the radio frequency spectrum, means
responsive to the detected output of said receiver
for producing indications representative of the
signals received within said spectrum, a signal
ing successive patterns representative of the sig
nals received during successive cycles of variation,
automatically comparing the time phase of the
signals of a pattern with the time of occurrence
recorder, and means responsive to a new signal 70 of signals received during a preceding pattern,
and detecting solely a new signal received by said
received within said spectrum which has not
receiver in said range which does not correspond
caused indications during the preceding scanning
in time phase with a signal of said pattern.
operations for operatively connecting said record
er to the output of said receiver, said last means
including a trigger circuit, an electron discharge 75
WARREN H. BLISS.
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