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Патент USA US2113371

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April 5, v1938.
Filed April 17, 1956
_Y1 .
-q 0000€
Ha race R. Dyson»
attorney „
Patented Apr. 5, 1938
Horace R. Dyson, Oaklyn, N. J., assignor to
Radio Corporation of America, a corporation
of Delaware
Application April 17, 1936, serial No. '14,852
(o1. 25o-_17)
My invention broadly relates to keying sys
tems. More speciñcally my invention is a key
ing system for high power radio transmitters in
which objectionable key clicks are- substantially
5 eliminated.
The keying of a radio transmitter involves
numerous diiiiculties.
Among these are `the in
terference problems caused by “key clicks” and
“key thumps”. Such interference is particular
10 ly objectionable when a number of transmitters
are operatedV in close proximity to a number of
receivers,-a condition often experienced on
When keyed transmitters and receivers are be
15 ing simultaneously operated in relatively close
proximity, the key clicks have been found to set
up transient currents in the receivers.
transient currents are caused by the abrupt
building-up and sharp decay of a keyed trans
mitter wave.
Numerous considerations make
the elimination of key clicks highly desirable.
One of the objects of my invention is the
elimination of key click or thump disturbances
in a transmitted wave.
Another object is to so shape the envelope of
the keyed transmitted energy that the inter
ference caused by such keying is substantially
eliminated by an inexpensive. and simply ar
tially biased negatively to> cut 01T the anode cur
rent of the power tube, and the power tube will
therefore not be. instantaneously energized.
Shortlyafter the iirst pair 3 of key contactsl
are closed the second pair 5 of relay key contacts 5
closes by means of a suitable mechanical con
nection between the pairs of contacts. This
short circuits the biasing resistor I3 and allows
the capacitor I5 to discharge through the re
sistor I1. Before the closing of the second pair 10
5 of key contacts, the grid electrode I9 of therm
ionic tube 2| was suñîciently negatively biased
by the potential across resistor I3 tocut-ofl‘ the
current tending to flow from the cathode 23 -to
the anode 25.
through the resistor I1 gradually decreases the
negative bias on the grid I9, thereby permitting
gradual building up of current through the
cathode, anode and anode circuit resistor 21. 20
The current flowing through the anode resistor
21 establishes a voltagedrop across this resistor.
This voltage minus the voltage dropacross the
bias resistor 29 will be applied to thescreen grid
II of the power amplifier tube I2. Thus, the 25
screen grid II which was initially negative with
respect to ground becomes positive and thereby
permits anode current to flow ,in Vthe ' power
ranged apparatus.
amplifier tube, which now assumes its normal
A further object is to gradually build up the
keyed wave and thereafter gradually reduce the
keyed wave to eliminate the disturbing effects
of abrupt keying.
An additional object is to make the key cllck
35 limiting device substantially independent of the
transmitted frequency and practical for high
keying speeds.
The gradual discharge of the capacitor I5
» The anode current flowing through the cathode
resistor 30l to ground produces a voltage drop
across the cathode _resistor which positively biases
the vacuum tube 3|. The anode battery 33 is
chosen so that substantially no current flows in
the field winding of the latching relay 35 when ’
My invention may be best understood by re
ferring to the accompanying drawing in which
40 Fig. 1 is a schematic diagram of one embodi
ment of my invention, and
the grid 31 is at zero voltage with respect to the
cathode 39. When the grid 31 becomes positive
with respect to cathode 39, current ñowing in
the ñeld winding of the relay closes the relay 40
contacts 4I which are in parallel with the relay
Fig. 2 (A, B, C) are illustrations of a conven
tionally keyed carrier wave, a carrier wave keyed
in accordance with my invention, and relative
45- keying characteristics of the several stages of a
transmitter keyed in accordance with this in
Referring to Fig. 1, a suitable key I is con
key contacts 3. Since the plate or anode cur
rent from the power ampliiier I2 varies during
keying, it is essential that the latching relay
contacts remain closed until the anode current 45
of the power amplifier practically ceases.
When the key I is opened and the keying re
lay is deenergized, i. e. during start of a space,
nected by relay means 2 to two pairs of relay
The relay is arranged so that
one pair of the key contacts 3 close slightly be
fore the other pair of contacts 5. This allows
the master oscillator and driver stages 1 to ener
gize the power ampliñer grid 9. However, the
55 screen grid Il of the power amplifier I2 is ini
the latching relay 35 contacts 4I, in parallel
with the relay key contacts 3, remain closed until 50
the power amplifier current nearly ceases. Dur
ing this last mentioned interval the second pair
of relay key contacts 5'open which allows bias
voltage to gradually build up across capacitor I5
50 key contacts 3, 5.
through resistor I1. The gradually increasing 55
bias slowly cuts oif the anode current in tube 2I.
Thus, the current through resistor 21, and the
shunting capacitor 28, is slowly reduced to zero.
Since the bias voltage on the screen grid II
depends upon the difference in voltage across the
anode resistor 21 and across the resistor 29, it will
be apparent that with zero voltage across the
bias resistor 21, the bias voltage on the screen
grid I I will be that across resistor 21` and will be
source, then removes the bias on the first of said
pair of tubes thereby permitting anode currents
to iiow, which currents remove the cut-oil’ bias
on said power amplifier, thereby biasing the sec
ond of said pair of tubes to maintain the keying 6
of said oscillator, and further arranged to re
store the aforesaid cut-off biases during spacing
before de-energizing said> source, of oscillation.
2_., A keying system for a source, of oscillations
negative with respect to its cathode 8. With the and a power amplifier connected to said source,
screen grid II negatively biased, the anode cur
_comprising means for keying connected to said
rent in tube I2 will become zero, the bias voltage source and to the first oi' said pair of tubes,
between the grid 31 and the cathode 39 of'tube a> painofv thermionic tubes, the iirst of said tubes
3I will be zero, the latching relay will. there- _ haring its output circuit connected to said power
fore open, and the master oscillator and' driver ampliñer, and thesecond of said tubes having its
stages thus de-energized.
input circuit connected to said power amplifier,
Thus, I have described how the master oscil
means connected to said pair of tubes and to said
lator and driver stages of a transmitter may be power amplifier for biasing each of said tubes
abruptly keyed and substantially no disturbance. y to cut-olf during spacing intervals, means in
will follow the keying because the power ampli
cluding said power amplifier for reducing the
fier is VgraduallyY energizedî after theY ñrst men
cut1-`oi’f:-lf»ias‘` of’ the second?oi` said tubes; means
tio'ned` keying and gradually cie-energized before including> said secondv tube for temporarily con
the keyed master oscillator- and' driver'stages are tinuing the keying: of said' source, means conile-energized'. The normal kcying'of' a continu
nect'edA to. said power amplifier for biasing said
ousv wave transmitter is> represented by Fig. 2A. power ampliñer to cut-orf during spacing signals,
Thefsharp buildingy up and rapid break establish and means> including thel ñrst of said tubes for
the interfering radiation. The characteristic opposing the cut-olf bias of said power ampliiier,
marking signal, represented byV Fig. 2B, shows wherebyI said keying means is so constructed and
the gradually f building. up and gradual 'reduction arranged' that a marking signal first keys said
ofj a4 signall or carrier current» keyed: in accord- source, then removes the bias on the ñrst of said
ance'with my invention. Fig. 2C'y is a graph rep
pair of tubes thereby permitting anode currents
resenting the relative keying, with respect to to flow, whichcurrents remove the cut-01T biasV
time, of- the master oscillator andi driver, andi on said power amplifier, thereby biasing the sec
power amplifier stages.
ondi of' said. pair: of tubes to maintain the key
The actual tube equipment, voltages, resistor
and capacitor valueswill be determined by the
type and power of thev transmitter to be keyed.
If a sensitive relayv of the proper characteristics
is employed, the vacuum tube 31| may obviously
40 be omitted and: the relay connected directlyY
across theA biasing resistor, or in series therewith.
The manufacturer’s normar ratings off the sev
eral parts may be' followed. By way of example,
one suitable'set of tubes, constants and volt
ages have been indicated onV theaccompanying
I claim as my invention:
l. A keying system for a source ofi oscillationsY
and a power ampliiierl connected tolsaid source,
comprising means for keying said source, a pair
ofïthermionic tubes connected'to said -power' am
plifier, means connected to saidï pair of tubes for"
biasing each of saidï tubes to. cut-off during spac
ing intervals, means connected, to said’ vpower'
55,. ampliñer and tothe iirst of.' said pair of tubes
for biasing, said power amplifier to. cut-01T` dur
ing spacing signals, means> including'the ñrst of
said; pair of tubes for overcoming the cut-ofi’
bias of' said power ampliiier, means> including
saidpower amplifier for reducing the cut-off' bias
of the second. of said. tubes, meansV including said
second' tube for temporarily continuing the key-l
ing of said source, and keying means connected
to said source and to the ñrst of said pair of
tubeswhereby a marking signalñrst keys said
ingof said oscillator, and further arranged to
restore the’aforesaid cut-oir biases during spac
ingv before: de-energizing said' source of oscilla
3’. A deviceV of the character of claim l further
characterized by the inclusion of means for
gradually energizing and gradually de-'energiz iov.
ing'said power ampliiier.
4;> A keying system for a source of oscillatory
currents and a power amplifier, including a
screen- grid', connected thereto` which comprises
a thermionic tube, meansl for biasing said tube
during-- spacingA signals to substantially cut-off,
meansl for'Y biasing- saidl screen grid to de-ener
gize said power amplifier,` a connection from said
tube to said screen grid biasingl means wherebyY
anode currents in saidv tube oppose the screen
bias-means, ¿means for keying said source, meansk
for removing- the bias on said tube and thereby
positively' biasing said screen. grid after sai-d
source is keyed, and means including saidpower
amplifier for continuing the energizationV of said
source until a spacingV signal substantially de
energizes saidpower amplifier.
5. AdeviceY of the character of claim 4 includ
ing means for gradually removing the bias on
said screen grid during marking signals and
gradually restoring said bias during- spacing
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