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Патент USA US3032759

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May 1, 1962
Filed Dec. 14, 1960
(fl + f2) 0R
fl AND (f|+f2)
fl AND (f|"f2)
F/G /
(fl'l' f2) OR
24 \25 27
4% REF
e /\ _
1/ i
REFERENCE f‘ \l______;
L____J‘ (26
F/G‘ 3
Patented May 1, 1962
_ The basis of the telemetering system of the present
invention resides in the combination at the transmitting
station of a reference and data signal to produce a third
Robert T. Hart, Richardson, Tern, assignor to Collins
Radio Company, Cedar Rapids, Iowa, a corporation
of these three signals over the transmission medium (wire
or radio). The receiving station is adapated to separate
the transmitted signals to regain the data signal in its
of Iowa
Filed Dec. 14, 1960, Ser. No. 75,760
5 Claims. (Cl. 340-198)
Signal and the subsequent transmission of a selected pair
original form. With reference to FIGURE 1, the trans
mitting station is seen to comprise a reference signal
This invention relates generally to data transmission 10 source 11 designated at frequency h. The transmitting
and more particularly to a data transmission system for
The art of telemetering encompasses the transmission
of information de?ning numerous conditions such as tem
perature, velocity, shaft position, etc. The transmission
of information may be through wire means or a transmis
sion medium such as radio vwaves. Unlike communica
tion systems for voice and other types of communication
data, a telemetering system ofttimes necessitates that a
station further comprises a second frequency source 10
in the form of a data information signal f2. It is to be
understood that the intelligence to be transmitted will be
imposed on the data information signal f2 such that the
15 intelligence may be regained by a comparison between
the data information signal f2 and the reference signal f1.
Each of the signal sources ]‘1 and f2 is applied to a
mixer 12. The reference signal fl is applied to mixer 12
through connector 13 and additionally to the output line
comparison or exacting reference be transmitted along 20 15. Mixer 12 develops outputs in the form of (fl-H2)
and (f1—-f2), either of which may be selectively passed
with the transmission data in order that the receiving
a band-pass ?lter 14 to the output line 15. Depend
means may re-create the transmitted intelligence. For
ing then upon the choice of ?lter 14, the output line 15
example, a telemetering system may involve the trans
is impressed with a composite signal which may be either
mission of a signal which may be in the form of a very
low frequency alternating-current signal or, perhaps, a 25 A and (f1+f2) or )‘1 and (f1—;f2). Thus, the transmis
sion consists of the reference signal f1 together with the
direct-current signal and such information may be mean
sum of the reference and data signals or the difference
ingless unless the reference with respect to which the
between the reference and data signals; the latter being
data signal was created or measured is precisely recreated
selected by band-pass ?lter 14. The output line 15 may
at the receiving station. A commonly employed tech
nique for re-creating a reference at the receiving station 30 be considered to connect to the transmission medium
which might be a wire or a radio transmitting and receiv
is the generation of a like reference at the receiving sta
ing system. The system is independent of this medium
tion with a synchronizing signal being transmitted to
and, therefore, no speci?c illustration thereof is included
obtain a system of automatic frequency control at the
in the drawings.
receiver. In such systems, however, errors may be in
FIGURE 2 represents the receiving station of the pres
troduced due to synchronization drift and phase shift and 35
invention where the transmitted combination signal
amplitude variations which may be introduced by the
(illustrated as input 15’) is applied to an ampli?er 16.
transmission medium. Such errors may be inevitable
It is to be understood that should the transmission medium
whether the transmission medium be a direct wire or a
be radio, the functional representation of FIGURES 1
radio transmission medium. The present invention has
and 2 would include conventional transmitting and re
an object therefore of providing a telemetering system
ceiving equipment (not illustrated). The receiving sta
of high versatility which exhibits less dependence upon
tion of FIGURE 2 functions to re-create the data and
the transmission medium in maintaining accuracy by in
reference signal in their original form and this is accom
corporating a common reference at the transmitting and
plished by a selective ?ltering and mixing scheme as fol
receiving ends of the system rather than by re-creating
45 lows. Output from ampli?er 16, which may be expressed
a reference at the receiving end.
as either ]‘1 and (fl-H2) or f1 and (f1—f2) (as deter
A further object of the present invention is the provi
mined by the bandpass action of ?lter 14 of FIGURE 1),
sion of a telemetering technique wherein the relationship
is applied through parallel channels 17 and 18 to ?lters 19
between data and reference signals is a constant and is
and 20 respectively. Filter 19 is a band-pass ?lter with
independent of the constants of the transmission medium.
the same characteristic as ?lter 14 of FIGURE 1. Filter
Still a further object of the present invention is the
19, as illustrated, passes either (fl-H2) or (fr-f2). Fil
provision of a telemetering system relatively noncomplex
ter 20 passes only the reference frequency f1 and passes
as compared to known systems with a decided improve
signal f1 to the reference output line 26. The reference
ment in accuracy and versatility.
signal 1‘, from ?lter 20 is additionally applied through
The present invention features a unique signal mixing
scheme whereby the reference signal may be exactly re 55 connector 23 to a mixer 21. The output from ?lter 19
produced at the receiver in a manner such that the data
signal may vary either in phase or amplitude with re
spect to the reference due to the maintenance of a pre
cise amplitude-phase relationship between the data and
reference signals throughout the system.
These and other objects and features of the present in
vention will be apparent from a reading of the following
description in conjunction with the accompanying draw
is applied as a second input to mixer ‘21. Mixer 21
develops an output 24 which is a re-creation of the data
information signal 1‘; and the fa component is selectively
passed by a further band-pass ?lter 25 to the data output
With further reference to FIGURE 2, an AGC regu
lator is associated with the reference signal ]‘1 and is com
mon to both channels 17 and 18. The f1 reference out
put from ?lter 20 is seen to be connected through con
ings in which:
FIGURE 1 is a functional block diagram of the trans 65 nector 27 to the regulator 28. The output 29 from regu
later 28 is applied to ampli?er 16. Thus, the system pro
mitting station of the system,
vides a constant amplitude reference signal by maintain
*‘WFIGURE 2 is a functional block diagram of the re
ing the gain of the system constant. The relationship be
ceiving station of the system, and
tween the data and reference signals is, therefore, a con
FIGURE 3 is a functional diagram of an embodiment
of the systems of FIGURES 1 and 2 wherein a shaft posi 70 stant relationship and is not dependent upon the constants
of the transmission medium.
tion may be precisely telemetered as a function of phase
The operation of the system might be further illus
shift between reference and data signals.
trated by a speci?c example. From an analysis of the
mixing scheme, it is apparent that the reference signal
f1 and the data signal f2 may be chosen as being equal,
wherein (f1+f2)=2f1=2f2 and (fr-)3) is equal to zero.
Thus, one might choose f1=f2=l500 c.p.s., where
(f1-i-f2)\=30O0 c.p.s. and (f1—f2)=O.
With this choice
of frequencies, ?lter 14 of FIGURE 1 would pass
mer-ated above have been operated with highly satisfac
tory results and have exhibited greater accuracy and less
dependence upon the transmission medium than known
The present invention is seen to provide a telemetering
system employing a unique application of known ele
ments in a less complex and more accurate system and
(fl-H2) or 3000 c.p.s. and two signals would be trans
which exhibits less dependence upon the transmission
mitted through the transmission medium; 1500 c.p.s.
medium by the novel incorporation of a common refer
reference and 3000 c.p.s. containing the data information 10 ence at both the transmitting and receiving stations.
f2. In this example, a single 3000 c.p.s. voice channel
Although this invention has been described with re
would provide su?icient bandwidth. At the receiving
spect to a particular embodiment thereof, it is not to be
station of FIGURE 2, the 1500 c.p.s. reference signal and
so limited as changes might be made therein which are
the 3000 c.p.s. signal containing the data signal are am
within the true scope of the invention as de?ned in
pli?ed in the gain stabilized ampli?er 16. Filter 19 would 15 the appended claims.
pass (fl-H2) or the 3000 c.p.s. signal, while ?lter 20
would pass the 1500 cps. reference signal f1. Mixer 2;’:
would develop an output (f1+]‘2)-f1=f2, which would
I claim:
1. A data transmission system comprising a signal
transmitting source and a signal receiving source, said
be selectively passed by ?lter 25 to produce the original
transmitting receiving sources being separated through a
f2 data signal at exactly the same frequency as that at
the transmitting station ‘and with amplitude and phase
linearity limited only by the mixers and associated am
transmit medium, means for generating at said transmit
ting source a reference signal f1 and a data signal f2, said
data system being variable in a predetermined manner
with respect to said reference signal, mixing means re
As previously discussed, the data signal f2 may be varied
ceiving said reference signal f1 and said data signal f2,
pli?er capabilities.
either in a phase or an amplitude relationship with re 25 a ?rst band-pass ?lter receiving the output from said mix
spect to the reference signal. FIGURE 3 illustrates an
ing means and selectively passing a predetermined mixing
embodiment of the telemetering system wherein the sys
tem may be incorporated to develop a direct-current volt
age output proportional to the phase displacement be
tween the reference signal fl and the data signal f2 as
a function, for example, of a shaft rotation at the re
ceiving station. With reference to FIGURE 3, the input
data signal f2 might ‘be developed from an electromechani
cal resolver 32. Reference signal fl is applied as a refer
ence input 11 to the circuitry of FIGURE 1 and is applied
additionally to the rotor 32:: of the resolver 32. Stator
winding 32c of resolver 32 then develops a signal f2 at
‘the h frequency but displaced in phase by an angle ¢
with respect thereto.
The outputs 26 and 27 from the
product of f1 and f2, the output from said ?rst band-pass
?lter and said reference signal applied through said trans
mission medium to said receiving means; said receiving
means comprising second and third band-pass ?lters re
ceiving said transmitted signals and selectively passing
said mixing product and said reference signal respectively,
a second mixing means receiving the outputs from said
second and third band-pass ?lters, a fourth band-pass ?l
ter receiving the output from said second mixing means
and selectively passing said data frequency component
f2, whereby the outputs from said second and fourth ?l
ters correspond respectively in frequency and phase to
said signal f1 and data signal f2 developed in said trans
receiving circuitry of FIGURE 2 would then be respec 40 mitting source.
tively the reference signal f1 and the data signal 54¢.
2. A data transmission system comprising means for
These signals are applied to a phase discriminator oil to
develop a direct-current voltage output 31 with magni
tude proportional to the phase shift </>. Phase shift qb,
in turn, would be proportional to an angular mechanical
input 34 representing, ‘for example, a shaft rotation of the
generating a reference signal and a data signal, said data
signal ‘being variable with respect to said reference sig
nal, means for combining said reference» signals to pro
duce the sum thereof and difference therebetween, means
for selecting one of said sum and difference signals for
resolver rotor 32a through an angle 6 with respect to the
transmission through a medium to a receiving means; said
rotor 320.
receiving means comprising ?rst and second selective ?l
The versatility of the telemetering system of the pres
tering means to respectively pass said reference signal
ent invention enables a wide variation in system opera
and said selected signal, mixing means receiving the out
tion. For example, at the transmitting station of FIG 50 puts from said first and second ?ltering means, third ?l
URE 1, a direct-current voltage might be developed in—
tering means receiving the output from said mixing means
dicative of some parameter to be telemetered such as,
and passing the component thereof corresponding to said
for example, a temperature or a pressure.
This direct
current voltage might be fed to a chopper to produce a
data signal.
3. A data transmission system as de?ned in claim 2
reference signal h of 1500 c.-p.s. and the data signal might 55 further including automatic gain regulating means receiv
then be developed as an output of either 1500 c.p.s. vari
ing the output from said ?rst ?ltering means, said regu
able phase or a variable amplitude as the station de
Still a further telemetering situation to which the pres
ent system is readily adaptable might be one wherein an
alternating-current signal of a lower frequency is to be
accurately relayed from the transmitting station to the
receiving station. This signal could be applied to a
chopper to convert to 1500 c.p.s. information and, at
lating means connected to and controlling the amplitude
of said reference signal and said selected signal as ap
plied to said receiving means.
4. A data transmission system as de?ned in claim 3
wherein said reference signal and said data signal are
equal in frequency, said selected signal equally the sum
of said reference and data signals, said ?rst ?ltering means
selectively passing said reference signal and said second
the receiving station, a direct-current voltage might be 65 ?ltering means selectively passing the sum of said ref
developed from. the 1500 c.p.s. data signal and a lower
erence signal and said data signal, said third ?ltering
frequency signal might be re-created by using an addi
means selectively passing said data signal.
tional chopper. The lower frequency alternating-current
5. A data transmission system as de?ned in claim 4
signal could then be recovered at the receiving station.
including data signal developing means for producing a
Although the speci?c examples illustrated herein were 70 data signal f2 equal to ii Let’), the outputs of said ?rst and
based upon the selection of a 1500 c.p.s. reference and
second ?lters being applied to phase discriminating means,
data signal, it is to be emphasized that the system lends
said phase discriminator means adapted to provide a
itself to a wide variation in choices of frequencies f1 and
direct-current voltage output proportional to the data
phase shift angle 45.
f2 consistent with the frequency separation capabilities of
the various band-pass ?lters. Each of the schemesvenu 75
No references cited.
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