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Патент USA US2136665

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Nov. 15, 1938.
A. w. BARBER- _
2,136,665 ,
RADIO TUNING INDICATION
Filed Feb. 118, 1956
Q2
FESRESELECTOR
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' AND RADIO FREQ.
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AUDIO
DETECTOR
AMPLIFIER.
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L
AMPLIFIER
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7
I.
59.1.
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SPEAKER
SPECIAL ‘ ‘
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DETECTOR
DIRECT“
CURRENT?
AMPLIFIER
-
LAMP
11v VENTOR '
2,136,665
Patented Nov. 15, 1938
‘ UNITED STATES PATENT ()FFICE
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2,136,665
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RADIO TUNING INDICATION
Alfred W. Barber, Flushing, N. Y.
Application February 18, 1936, Serial No. 64,517
4' Claims. ‘ (oi. 250--4o)
operation the long time constant diode load
This present invention of mine concerns im
provements in tuning indicator methods and charges up as the receiver is tuned thru a signal
means, adapted for use in radio receivers and to a maximum voltage point the value of which
‘ the like.
depends on the signal strength. Since the time
‘
One object of my invention is to provide a
tuning indicator which operates to indicate cor
rect tuning in radio receivers and the like. An.
other object is to provide such an indicator which
constant is large, the circuit holds this voltage. 5
as the receiver is tuned beyond the signal. On
the other hand, the short time constant circuit
gives‘a sharp indication regardless of the strength
10 of the signal being tuned in. Still another ob ject
as the signal is tuned out again. Thus one volt
age indicates the maximum signal strength and
the other indicates the instantaneous'signal or
tuning point. If an indicator is attached which
operates when both voltages are equal, the indi
cator will show exact tuning as exact tuning exists
only when both diode voltages are equal at max 15
is to provide a tuning indicator‘ which operates
by means of a lamp which lights when a signal
is correctly tuned in and operates by automatic
electrical means.
In continuously tunable radio receivers
em
ploying automatic volume control, the point of
exact tuning is _‘difficult to locate by ear, due to
the fact that in passing thru a signal the auto
matic 'volume control system follows the signal
2 O variations tending to keep the loud speaker out
put constant. In order to make accurate tuning
possible a number of different indicators have
been devised. The most Widely used indicators
are meters or lamps actuated by plate current
25 changes in the ampli?er tubes controlled by the
. automatic volume control.
Correct tuning is in
dicated by a minimum ampli?er ‘tube plate cur
rent or maximum plate voltage due to the action
of the automatic volume control voltage. These
systems operate much better on strong signals
than on weak ones and may even ceaseto operate
on signals below a certain level. The apparent
sharpness of the indication also varies with signal
strength, since moving say 5 kilocycles on a strong
station may actuate an indicator much further
than 5 kilocycles change on a, Weaker station.
charges up with the signal but discharges again
imum response.
The appended claims set forth, in particular,
the novelfeatures to be found in this invention.
The following description, however, when taken in .
connection with the drawing, will serve to set
forth the theory and mode ofroperation of my
invention.
_
In the drawing-
,
'
Fig. 1‘ shows 'a'block diagram of the general
form of my invention.
_
25
vFig. 2 ‘shows a circuit of an indicating system
embodying my invention.
‘
Fig. 3 shows a circuit equivalent to one mode of
operation of the circuit of Fig. 2.
Fig. 4 shows a circuit equivalent to another 30
mode of operation of the circuit of Fig. 2.
Fig. 5 shows a circuit of another form of my in
vention.‘
V Fig. 6 shows curves of voltages generated by
various forms of my invention. a
35
The block diagram shown in Fig. ‘1 indicates
the general form of my tuning indicator system.
A conventional automatic volume control receiver
In my copending application for Letters Patent
entitled “Recti?er circuits” ?led January 30, 1 936,
and bearing Serial No. 61,457 I have shown a - system is indicated including a “pre-selector and
40 recti?er circuit having some unique properties. radio frequency ampli?er”, a “detector”, an
This recti?er circuit is used in my present tun
“audio ampli?er” and a “loud speaker”. At the
ing indicator system.
output of the “radio frequency ampli?er” and in
My present system‘ of tuning indication over- ‘
comes the dif?culties pointed out above since the
45 indicator‘ flashes on at correct tuning giving a
Very sharp indication and operates with equal
sharpness on‘ strong ‘or weak signals. I employ
two diode circuits rectifying the carrier frequency
output of the radio receiver. One diode circuit
parallel with the “detector” is connected‘ my
“special detector” generating an indicator con
trol signal. The generated control signal is am- 45
pli?ed by a “direct current ampli?er” and then
actuates the “lamp” or other indicating device.
While the invention is not limited by the point of
connection of the “special detector” this will be
0 has a long time constant load circuit and the other
the usual point as the radio or intermediate
‘frequency voltage is a maximum at this point.
Fig. 2 shows a circuit diagram of one form of
ful output is the difference between the voltages
my tuning indicator disengaged from the rest of
generated by the two diodes and it may be ampli
fled by a direct current ampli?er, and used to the receiver. It embodies the double diode recti
‘diode a short time constant load circuit. The use
55 actuate a lamp or other indicating device.
In
?er tube I, which may be two separate diodes as 55
2
2,136,665
well, the direct current ampli?er tube 2, and the
indicating lamp 3 which may be some other type
of indicator such as a meter or light shutter.
The unrecti?ed voltage is introduced into the
diode circuit by means of the transformer having
a primary 4 and a magnetically coupled secondary
5. This transformer may be a part of the re
ceiver or may be a branch circuit for the tuning
indicator and capacity coupling may be used to
The pri
mary will in general be connected in parallel with
10 coil 5 doing away with the primary 4.
the regular receiver detector as shown in Fig. 1.
The alternating current voltage appearing across
coil 5 is impressed on the two diodes, thru the
15 independent load circuits consisting‘of’ resistor
6 by-passed by condenser ‘I and resistor 8 by
passed by condenser 9. The diodev cathodes I0’
and resistance 8 in parallel is low enough so that
the voltage across condenser 9 follows the signal
variations due to tuning, the net voltage across
points 2| and 22 will ‘indicate the tuning condi
tion.
If the tuning is carried to a point where no
signal is picked up, the voltage across condenser 9
drops to zero and the point 2I is positive with
respect to ground by the voltage of battery 20.
Now if the tuning is returned to the signal, as the
signal is tuned in the voltage across condenser 9 10
builds up and the net voltage between point 2I
and ground drops. When the signal is again
tuned into maximum response, the voltage across
condenser!) equals the voltage of battery 20 and
the net voltage between point 2I and ground is
ZerO.
'
t
r
'
While not limited to these values, I have found
and II are connected together and to one end of ‘ that in'ge'neral the time constant of condenser ‘I
input coil 5. A common cathode may be used in parallel with resistor 6 should be greater than
20 in place of cathodes I0’ and II. The resistor 6 one second and the time constant of condenser 9 20
condenser 'I load is in series with coil ‘5 and in’para'llel with resistor 8 should be less than
diode anode I2 and the resistor 8 condenser 9 one second for the best operation of my system.
load is in series with. coil 5 and the other diode
When the actual circuit of Fig. 2 is used, the
anode I3. The diode anode I2 is connected to condenser ‘I charges upon the ?rst excursion thru
ground or reference potential point G and the the signal establishing the reference voltage
recti?ed output is taken off between anode I3
and ground or reference potential point G. Some
of the properties and uses. of this circuit are
pointed out in my previous application referred
to above. The present description will be limited
to its functions and characteristics-as used in my
tuning indicator.
. .
" »
The voltage difference between anode I3 and
ground is impressed on grid I4 of the direct
35 coupled ampli?er tube 2 by direct connection.
Tube 2 may be a multi-grid tube but is shown as a
triode havingcathode .I5, grid I4 and plate I6.
,A steady'grid bias'is impressed on tube 2 by bat
tery E0 connected between ‘cathode I 5 and ground
40 G; The indicator part of the circuit consists of a
neon or gas ?lled glow lamp 3 parallel fed from
plate I6 and alternating current source ‘I'I thru
variable resistor I8. The alternating - current
‘source Il may bethesecondary of a transformer
45 with primary I9 connected to the alternating
current power lines. In‘operation the ‘resistor
I8 and the plate resistance'of'tube 2 act to divide
the‘voltage from secondary 11. If the grid I4 is
made more positive or less negative the plate re
sistance
of tube 2 decreases, There will be a crit
50
ical biason grid I4 such‘ that lamp 3 just lights
on the peaks of the alternating current wave for
particular values of resistor I8 and voltage across
secondary I1. If EC is made equal to this critical
55 bias and the only voltage’ placed on grid I4 is
positive with respect to ground, lamp 3 will only
light when zero voltage is placed on grid I4. ~ The
operation of the indicator depends on the pro
duction of zero net voltage by the recti?er when
60 the receiver is exactly tuned.
‘
Fig. 3.is useful in explaining the operation of
Fig. 2. "If the time constant of resistor 6 shunted
by condenser ‘I is made long,,increases in input
signal will build up the charge in condenser ‘I
but decreases in signal will leave the charge to
‘discharge slowly thru resistor 6. If the circuit
of Fig. 2 is attached to a radio receiver and the
receiver vis tuned thru a signal, the voltage across
condenser ‘I will build up to a maximum value
equivalent to battery 20 and the voltage supplied
to grid I4 from the recti?er drops to zero only
when the tuning is restored to the point giving
maximum response. As explained above the
lamp 3 is thus caused to light when no external
bias is fed to grid I4 which takes place only at
exact tuning of the receiver.
Fig. 6 shows curves “of the voltages produced
in the recti?er circuits of Fig. 2 upon tuning thru
a signal. Curve a represents the steady positive 35
reference potential established in condenser l
upon'tuning thru a signal. The difference be
tween curves 0 and b is the voltage across con
denser 9 upon tuning back thru the signal and
curve I) is the net voltage passed on to grid I4. 40
This shows that this net voltage is zero at h which
point is the point of resonance for the tuning
system. For the purpose of allowing reasonable
tolerance in the system it may be necessary to
allow lamp 3 to light whenever the external volt 45
age applied to grid l4’ falls below say 0.5 volt.
These limits are indicated on Fig. 6 by line e at
0.5‘ volt or whatever arbitrary voltage is chosen.
The intersection of c with b shows that under
these conditions lamp 3 will light from g to 7' 50
which may for instance correspond to 1000 cycles
'either'side of exact tuning.
Fig. 5 shows a circuit in which lamp 3 is con
nected in series with the ampli?er tube plate.
The recti?er I is inverted so that the load circuits
are in the diode cathode circuits. This reverses
the polarity of the recti?ed voltages with re
spect to ground when cathode I0 is grounded and
the output is taken off between cathode I I and
ground G. If, as before, the time constant of re 60
sistor 6 and condenser ‘I in parallel is made long,
a reference potential diiference c’ as shown in Fig.
6' will be established across condenser ‘I. Upon
tuning thru a signal the net voltage between
cathode II and ground G will follow curve (1 65
and the net voltage will be zero at exact tuning.
With lamp 3 in series with the plate I6 of tube
replaced by battery 20 with the negative end
2 and in parallel with resistor I8, the supply
voltage EB plus the alternating current voltage
‘across transformer secondary I‘I divides between 70
resistor I8 and the internal plate resistance of
tube 2. If bias E0 is made such that lamp 3 just
lights with zero voltage supplied to grid I4 from
the recti?er circuit, lamp 3 will be extinguished
grounded. If the time constant of‘ condenser 9
as soon as the plate resistance is increased, since 75
770 proportional to the amplitude of the signal and
‘will hold this’ voltage. Fora short time there
.after the recti?er circuit acts like the circuit in
Fig. 3 in which the voltage across condenser ‘I is
\
increasing the plate resistance lowers the voltage
drop across the resistor 18 and lamp 3. The plate
resistance increases in tuning over curve dexcept
at exact tuning. Thus the lighting of the lamp
Ci indicates exact tuning.
The recti?er part of Fig. 2 can be reversed mak
ing the series lamp connection possible simply by
reversing the long and short time constant loads.
This is shown in Fig. 4 where the battery 20
equivalent of the long time constant circuit is in
series with anode i3 and the resulting voltage is
negative except at exact tuning.
Similarly the
recti?er part of Fig. 5 may be reversed permitting
the parallel fed indicating lamp with this recti?er
connection.
The various systems may also be set-up so
that at a critical bias the lamp goes out and
the bias from the recti?er keeps the lamp lighted
except at exact tuning.
3 .
2,136,665
This is accomplished
20 by interchanging the series or parallel lamp con
nection with the parallel or series connection.
In this case the lamp extinguishes at exact tun— ,
mg.
In general gas ?lled glow lamps which I pro
pose as suited to this tuning system require a
higher voltage to break down than to extinguish.
For instance a lamp may not light until the
voltage across it is 100 volts but upon reducing
between the two said unidirectional voltages is
less than a predetermined amount.
2. In a tuneable carrier wave receiver, the
combination of a tuning lamp, a thermionic
vacuum tube ampli?er including a grid, a cath
ode and a plate and a recti?er including two
rectifying circuits, means for applying carrier
voltage to said recti?er, means for producing a
voltage proportional to the peak unmodulated
carrier voltage applied to said recti?er and means 10
for maintaining said voltage substantially con
stant for a predetermined period of time greater
than the normal time required to tune said re
ceiver thru a desired carrier in one rectifying
circuit of said recti?er, and means for produc
ing a second voltage proportional to the instan
taneous peak unmodulated carrier voltage ap
plied to said recti?er in the other rectifying cir
cuit of said recti?er, means for applying a volt
age proportional to the di?erence between the 20
two said recti?ed voltages to the grid'of said
ampli?er and a series circuit in the plate cir
cuit of said ampli?er including said lamp and
a source of alternating current whereby said
lamp operates when said voltage difference is 253
less than a predetermined amount.
- 3. In a carrier wave receiver, the combination
of a gaseous glow lamp, receiver tuning means, a
the voltage, the lamp may remain lighted until , thermionic vacuum tube ampli?er including at
the drop across it falls to 80 volts.
A lamp
of this type in my tuning system, with direct
current only on the ampli?er tube plate, will
show a drag in the direction of the tuning due
to this difference between ignition and extinc
tion voltage. By using an alternating current
Voltage in series with the lamp having an ampli
tude greater than the difference between ig
nition and extinction voltages the lamp is turned
40
on and o? at an invisible rate preventing any
drag effect. If the tuning is carried to a point
' below the ignition condition, the alternating cur
rent turns the lamp off and it does not ignite
again until the tuning is returned to a favor
able point. Thus the visible indication follows
the ignition condition curve regardless of the
lag or drag eifect in the lamp.
While I have described only a few systems
whereby my invention may be carried into effect
and have pointed out a few possible variations,
it will be apparent to one skilled in the art that
many modi?cations are possible without de
parting from its spirit and scope as set forth
in the appended claims.
What I claim is:
I
1. In a carrier wave receiver, the combination
of receiver tuning means, a tuning indicator and
a recti?er comprising two rectifying circuits,
means for applying carrier voltage to said recti
?er, means for producing a unidirectional volt
60 age proportional to the maximum amplitude of
a carrier voltage applied to ‘said recti?er and
means for maintaining said unidirectional volt
age substantially constant for a predetermined
period of time, means for producing a second
65 unidirectional voltage proportional to the in
stantaneous amplitude of said carrier voltage
applied to said recti?er and means for operat
_ ing said tuning indicator when the difference
least a grid, a cathode and a plate, and a recti
30
?er including at least two ‘rectifying circuits,
means for applying carrier voltage to said rec
ti?er, means for producing a voltage propor
tional to the amplitude of the carrier applied to
said recti?er at receiver resonance with said 85
carrier and means for delaying the decay of
this voltage so that its decay lags substantially
behind the decay of carrier voltage applied to
said recti?er due to tuning said receiver away
from said carrier in one rectifying circuit of 40
said recti?er, means for producing a second
voltage proportional to the instantaneous ampli
tude of the carrier applied to said recti?er in a
second rectifying circuit of said recti?er, means
for applying a voltage proportional to the dif 45
ference between said two recti?ed voltages to
said grid and means for operating said glow lamp
from the plate of said ampli?er when the differ
ence between the two said recti?ed voltages is
less than a predetermined amount.
50
4. In a carrier wave receiver, the combination
of a gaseous glow lamp tuning indicator, an
ampli?er tube including at least a grid, a plate
and a cathode and two diode recti?ers, a load
circuit having a time constant greater than one
second in series with one of said diodes and a
load circuit having a time constant of a small
fraction of a second in series with the other of
said diodes, a connection between one end of
each of said load circuits and a common in 60
put circuit, a connection between the remain
ing end of one of said load circuits and ground
and a connection between the remaining end
of the other of said load circuits and the grid
of said ampli?er, a connection between said 65
plate and said lamp whereby said lamp glows
when said receiver is adjusted to maximum re
sponse with a carrier wave.
'
ALFREDW. BARBER.
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