Pulse-operated receiver
United States Patent 1 Odams l l PULSE-OPERATED RECEIVER [111 3,875,518 5] Apr. 1, 1975 Primary Examiner-Stanley T. Krawczewicz 75 Inventor: Charle E. d ms, Lo d d l l N H S a n on any Attorney, Agent, or F1rm-Robert G. Crooks;  
 &#39; Jefferson Ehrlich [73] Assignee: American Standard Inc., New York,  
  NY. 57 ABSTRACT [22] Filed; May 10, 1973 Disclosed is a receiver for a navigation system of the Omega type which operates with pulse-modulated sig- [211 Appl&#39; nals. The phase of received and local signals is com- Related US. A li ti D t pared by quantized pulses; phase equalization, com- {62] Division ofSer. No. 889,368, Dec. 31, 1969v Pat. No. f gate Phase and f f 3,313&#39;477 zation of gate patterns with timed-sequence Input s|gnals are obtained by pulse insertin into, or deletion 52 us. Cl 328/155, 324/83 FE, 328/134 from, signal loops which contain phase detectingv 151 int. Cl. H03b 3/04 quemial Signal Selecting. and readout control p 5 1 Fieid f Search 324 3 2 3 nents. Phase coincidence is counted cumulatively and is electromechanically stored. Lane position is re- 5 References Cited corded by pulse insertion. Components are con- UNITED STATES PATENTS structed and interrelated to reduce noise and improve 7 973 870 2/1960 t I 3 FE selectivity to enhance the benefits obtained by pulsed lguorie a. .t 3.430.234 2/l969 Wright 324/85 comm 3.579.128 5/1971 Smith et a! 328/ 3 Claims, 19 Drawing Figures lo Y Z I33 lflc&#39;Y again r-1 raw? PH/fSf I32 xon: WY gasses. WWW;  
 1/6 #7 n: [AC/1&#39; r0 fOUK fat/71am B&#39;LATERAL p s/razr an:  
 GflTES PULSE CKT. ,2; [2/ new&#34; 6.5 lg-l uiiiillz&#39;f cau/vmz LOOP svncunouums I C/IRCUIT Mm was /29 El/4 A22 &#34;GENERMOR fol/1? zt/ws [Ac/l To RE FE RENCE 2040 rwo(+,-) sflazrinres I26 OSCILLATOR A24 SYNTHESIZER PlPE GENERATOR CHART RECORDER DlSPLAI PHASE DETECTOR SHEET C18? 12 JI L JI L T Q3 gamma Hm ER 5N j mmBz M m3 W 983 NQNQ PULSE-OPERATED RECEIVER This is a division of application Ser. No. 889,368,  
 filed Dec. 31, 1969, now issued as U.S. Pat. No. 3,818,477.  
 BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to radiowave communication systems (Class 343), and particularly to transmitting beacons of the isophase type producing positiondeterminative signals (Subclass 105).  
 2. Description of the Prior Art The rapid increase in volume and speed of long distance ship and airplane traffic has increased the requirement for a reliable worldwide navigational system. It has been found that very-low-frequency (VLF) signals, e.g., on the order of K I-Iz., have suitable propagation characteristics in that they are detectable at great distances from one transmitting station and they are characterized especially by very-high, phase-delay stability, thus, the phase at a particular position on the earths surface is predictable by use of these signals. Therefore, navigation systems operating at these frequencies and based on phase-comparison technology are particularly useful. Several variations of such systems have been investigated. Installations which furnish hyperbolic lines of position defined by phase differ ences of time-shared signals from several transmitting locations are preferred. The reliability and phase stability of VLF propagation makes possible the use of verylong-range, accurate, position-determining signals for establishing a hyperbolic line system wherein position is defined by the points of phase coincidence of a pair of signals received respectively from each of at least two precisely synchronized transmitters. The hyperbolic lines of position are plotted, for instance, on a navigation chart, to produce grid lines, and these lines are separated by lanes&#39; whose width depends on the wave length of the transmitted signal. Phase coincidences of a synchronized, wave generator on the ambulating craft whose position is to be determined with the signals producing the grid lines traversed by the craft furnish a fix and course trace. In order to obtain a fix, signals must be received and processed from at least three transmitting stations. One system of the type described is the OMEGA Navigation System. The Omega system and other similar systems are described in the literature, for example, in Selected Papers Related to LongRange Radio Navigation presented at the Congress on Long-Range Navigation held in Munich, Germany, during 26-3l Aug. 1965 and reprinted by the Omega Implementation Committee for the United States Navy Department. U.S. patents classified, as indicated above, also deal with this subject matter, for example, U.S. Pat. Nos. 2,778,013, 2,855,595, 3,209,356, 3,263,231 and 3,388,397.  
  All receivers presently used in these navigation systems are known to have limitations affecting their use. They are bulky, and they are difficult to operate thereby necessitating the use of skilled, trained personnel. Additionally, the receivers are inaccurate and are not as reliable as they need to be in this application. They are expensive and are not suitable for semiautomatic or automatic operation, thus they are not suitable for use in modern, high-speed air and space craft.  
 SUMMARY OF THE INVENTION It is, therefore, an object of the invention to provide an improved navigation system receiver.  
  An additional object is to provide a navigation system receiver capable of fixing the position of a craft with a high degree of accuracy.  
  In the embodiment described, the invention is characterized by the use of pulse-signal or digital circuitry wherever possible, for intercircuitry signal-trains as well as output signals; the circuitry functions being defined in terms of pulse insertion and deletion, of pulse amplitude, duration and position modulation, of pulse quantizing, of pulse multiplexing, and of counting and storing of information-carrying, pulse trains. This characteristic concept is applied, directly, or indirectly, for its ultimate purpose, to various components of the navigational system, which comprises a local reference oscillator, a phase error detector, a selector for separate comparison of the several received time-shared signals with the local time reference, circuitry for matching the local phase with the phases of selected, received signals, and tracking apparatus for translating phase differences into terms of the hyperbolic grid.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and la are schematic diagrams which, together with a tabulation contained in the description and referring to these figures, illustrate the general structure and operation of the present system in easily comprehensible fashion;  
  FIG. 2 is a simplified block diagram of the complete system emphasizing, as distinct from FIG. 1, circuitry lines rather than functional interrelation; the identify ing numerals of the blocks correspond to those of FIG. 1; groups of blocks in dotted line frames which incorporate the above-characterized inventive aspects are marked with capital letters;  
  FIGS. 3, 4 and 5 are detailed circuit diagrams of the phase equalization group, within dotted line, frame A; the wiring of the detail circuitry of this group and of the other groups is completely evident from the respective figures, and their description is completed by a tabulation referring to the numbers marked on these figures and giving the names, ratings, or other identifications of the circuit elements;  
  FIGS. 6, 6A, 6B, and 7 are detailed circuit diagrams of the signal segregation group, frame B;  
  FIG. 8 is a detailed circuit diagram of the cumulative counting group, frame C;  
  FIG. 9 is a timing diagram illustrating the operation of the storage and count-out circuitry, group C;  
  FIG. 10 is a detailed circuit diagram of the comparator and coil driver;  
  FIG. 11 is a detailed circuit diagram of the lane position recording group, frame D; and  
  FIGS. I2, 13, 14, IS and 16 are detailed circuit diagrams of the amplifier group, frame F.  
 DESCRIPTION OF A PREFERRED EMBODIMENT General Outline With reference to FIGS. 1 and la, an operational description of the system as a whole with some simplifications, will first be presented in the form of a tabulation which combines references to the function blocks of FIG. I with their operations correlation. The blocks are 3 identified by identical numerals in both the tabulation and in FIGS. 1 and la.  
  As mentioned above, four transmitters, with their respective signals phase-synchronized, are assumed for purposes of the present description. The signals from the respective transmitters are indicated in FIG. 1 at a, 10b, 10c and 10d. As indicated, each transmitter transmits for a given period of time, a, b, c, d, and the transmitting periods of each transmitter is staggered with respect to all other transmitters. FIG. la schematil0 cally represents two hyperbolic lane systems established by transmitted signal pairs, such as a, b and c, d,  
 respectively, and forming, when superimposed. a nearly rectilinear grid. While FIG. la shows the plotted signals from the four transmitters 10a, 10b, 10c, 10d and their hyperbola axes, it will be understood that the spatial relation of transmitters and grid is grossly distorted, as indicated by the broken axis lines. It should be noted that FIG. 1 and the tabulation set forth in the following material include only the components necessary to process the signal from one transmitter, although the number of components required for processing all the signals in a complete system, as described, is indicated by legend.  
  lnput Output Mark Name from Operation to l 10a Plurality Transmit synchronized VLF (l0.2 KC) signals in 1 10b (here four) timed sequence for corresponding receiver l lOc of transchannels I l l mitters ll 1 Antenna and I I0 Receiving antenna for l0.2 KC signal, and H Coupler u,b,c,d coupling with amplifier l lZa RF l l l Distributed filter and limiter amplifier with l 12b Amplifier optimal phase constancy 1122 1 l2a Superheterodyne amplifier furnishing sinusoi- 1 l6 Amplifier ll4s dal 6.8 KC signal I23 1 Reference 129 Generates stable pulse train. continuous at Oscillator 2040 KC, for amplifier, timing function with Local generator and adder subtractors. Feeds into 1 5 local synthesizer H4: which supplies l7 KC signal after division by [20 signal after division by 120 1 l5 Timing Funcl22 Generates commutation pattern for segregating 1 timed sequence signals a, b. c, d in timed 1 p sequence. Pattern synchronized with patterns of a. b, c. d 125 126 132 [I6 Phase Error l2 Compares signals a, b,c, d with local square I 17 Detector l2l waves from tracking synthesizers 20. Furnishes DC voltage going from --0.5 to +0.5 volts as phase error goes from to +90 117 Bil l H6 Analog-digital converter of DC. phase error Pulse signal into pulses at corresponding frequenl D cies from zero pps for zero volt to 30 pps for 0.5 volt. Pulses corresponding to and volt on corresponding andoutput lines p and n Slim! gales l l Segregate four tracking loops for the four I1 F r P ir 1 l7 signals a, b, c, d by way of timing signal 125 P&#34; 117 signals a, b, c. d by way of timing signal 218&#34; h nn l) from 1 l5 and p and n signals from I 17. Open slightly shorter than a. b.c. d sequences e c.  
 [19 Adderl 14 Combine p, n pulses from 17 and l 18p. ll8n 120 219 Subtractors l18p with continuous pulse train 2040 KC from 1 I4, 319 Four (one llBn inserting or canceling a 2040 KC pulse for M9 per channel) each p, n pulse respectively 120 Tracking 9 Frequency dividers counting down by a factor 121 220 s h i of 300. Furnish 6.8 KC square waves with 129 320 Four (one phases advanced H300 of a cycle for each I30 420 per h fl) pulse added and retarded I I300 for each pulse deleted. Continuous 6.8 KC output signal. Once phase lock with 1 l2 is established, 1 l7 ceases to furnish p, n pulses. The pulses fed from M7 to I25, I26, measure the phase lead or lag of the signals from l0, quantized at 1/300 cycle. 121 Four Long 120 Close the tracking servo loops 19. 20 back to H6 Gates 116. Driven by ll8p. 11811 from 115. synchronized with a. b. c. d Open for full 0, b. c. d  
 Continued Mark Name Input Operation Output from to I22 Sequential I Hi Causes pulses from I24 to be added or deleted I Channel I I4 until coincidence is reached between gate Synchroniz- I24 pattern of I I5 and a. b. c. d envelopes from ing Circuit I24 as observed at I33 when 124 is manually stopped I24 Pipe Manually controlled, furnishes pulses to be Generator added or subtracted at I22 I2 125 Add Counter l lllp Sum add pulses from l l8 of one channel with I27 Stores l Ilia subtract pulses from 218&#34; of another channel.  
 Feed into comparator and coil driver I27 I26 Subtract l [Hp Sum subtract pulses from l l8&#34; of one channel I27 Counter l lltn with add pulses front I 18p of another channel.  
 Stores Feed into coils I26.l  
 I27 Comparator I Prevents counter from being driven in both I275 Coil Driver I26 directions simultaneously I275 Counters I27 Electromechanically record continuously the OUTPUT net difference provided by I 27. this being the change of one centilane IZK Synthcsiver I I4 Develops 6.8 KC for I29 I29 I23 I29 Loop Digital I20 Detects phase difference between I I4 and one l [4 Phase preferred (usually the strongest received] Detector loop of I20 (one of u. h, r&#39;, d), to lock I I4 to respective sender. in digital terms I30 Display I20 Compare 6.8 KC output signals of pairs I9. 20. I3]  
  Phase Furnish ramps from zero to maximum correspond Detectors ing to phase differences from zero to full cycle I31 Chart I30 Graphically record the lanes crossings as ()L&#39;TPL&#39;T Recorders lines traversing the chart relatively to a time base I32 Envelope I III? Develops envelopes ofa. h. 1, 11 I31 Detector l 28 I33 Envelope I I5 Presents a. h, c. d envelopes and commutation ()L&#39;TPL&#39;T Scope 132 pattern in dual trace against same time base to display synchronization In order to facilitate a concise description of the embodiment and to correlate the same to the claimed structure, subdivision headings have been arranged to identify the previously mentioned frames,&#34; marked with capital letters in FIG. 2. Respective blocks of the Schematic Drawings and frames are marked with numerals which correspondingly recur in all figures.  
  Where it is appropriate to the description, interconnections between the various components are marked with labels coded to indicate the blocks by their respective numerals and are further labeled by i&#34; for input and o for output, respectively, for example, i 112 is the input terminal from block 112, and o 112 is the output terminal to block 112.  
 A. Phase-Locked Loops Referring to FIGS. 3, 4 and 5 which discloses a phase-locked loop, frame A, including blocks such as 116, 117, 119 and 120, and refer additionally to FIGS. 1 and 2 in order to correlate the description to the system operation. Each transmitted signal from stations 10a, 10b, 10c and 10d is tracked in a respective servo loop which is adapted to develop a continuous local signal which is phase-locked to the intermitten transmitted signal. For instance, a single reference oscillator 114 (FIG. 2) provides a local, precision, phase signal for all servo loops. Each respective loop includes a common. phase-error detector 116 which compares the signal from mixer 11% with a corrected, local signal derived from reference oscillator 114. The phaseerror detector 116 has a DC output which is positive, negative, or zero depending on the phase difference be tween the compared signals. This DC output is fed to and controls a bilateral pulse generator 117 which is common to each loop but has two output lines; one line carrying pulses corresponding to a positive phase difference, the other line carrying pulses corresponding to a negative phase difference. The two output lines are coupled through commutating gates, to be fully described under B, 118p, 11811, 218p, 218n, 418p, 4l8n, sequentially to each one of four local slave channels including, respectively, an addcr-subtractor 119, 219, 319, 4l9 and a divider 120, 220, 320, 420. The function of each adder-subtractor, such as 119, is to adjust the 2040 KC reference oscillator signal, from 114, by either adding a pulse for each positive pulse from generator 117, or deleting a pulse for each negative pulse from generator 117. The following dividers 120, I20, 320, 420 convert the adjusted 2040 KC signal to the 6.8 KC signal which is to be compared in phaseerror detector 116. Each pulse addition in addersubtractor 119 changes the phase of the 2040 KC signal by 360. After division by a factor of 300 by divider 120, the net effect on the 6.8 KC comparison signal is to make a phase change of 12 or l/300 cycle therein.  
  As the receiver is moved with relation to the transmitting stations. the phase of the received signal changes, and the phase of the local comparison signal must be changed to maintain coincidence. The pulses which correct the phase of the local comparison signal serve as a measure of change of phase, and therefore of receiver change of position with respect to the respective transmitting stations. By properly comparing the number of positive and negative pulses produced in phase tracking a pair of transmitting stations, as will be hereinafter explained with reference to frame C, it is possible to determine where the receiver lies within the lanes and centilanes (FIG. la) which are characteristic of the Omega navigation system.  
 I. Phase-Error Detector 116 (FIG. 3)  
  Phase-error detector 116 compares the 6.8 KC input signal, derived in mixer ll2b from the transmitting station 102 KC signals a, b, c, d, with the corrected 6.8 KC comparison signal from the appropriate local channel, as follows. Transistor Qla constitutes an emitter follower amplifier for the signal received at input 1&#39; 112b. This signal is fed through the two diodes Dla and D20, connected in push-pull arrangement, through balanced transformer Tla and capacitor C30. Transistor 02a constitutes an emitter follower amplifier for the reference signal from terminal i 121, which is fed as a singleended signal into both diodes D1a and D2a through the transformer center-tap. The diodes D10 and D20 act as gates controlled by the reference signal, and operate to pass alternate sections of the 6.8 KC input signal. Since each tracking loop or channel is gated to correct phase every time its associated transmitter signal is received (approximately once every ten seconds in conventional Omega practice), the phase detector 116 will make small corrections and operate near zero output.  
  The signal passed by diodes D10 and D2a is integrated by capacitor C4a to remove high-frequency AC components, and is then fed to an operational integrater including amplifier ARla having feedback components R9a, C50, R8a. The operational integrater reduces the high frequency components of the phaseerror signal and provides sufficient DC gain to negate the effects of offsets caused by drift which is associated with a bilateral pulse generator of the type described below.  
  The servo loop gain is determined by the DC gain of the phase-error detector and the time constant of the bilateral pulse generator. This design provides a noisefree, phase-tracking velocity of approximately 3.6 microseconds per second or a bandwidth in this instance of 0.036 cycles, approximately. The performance of this noise free bandwidth, examined in an input signal to noise ratio of 1/10 in a 100 Hz bandwidth, yields a microsecond lag-angle of a baseline velocity of 35 knots, which is deemed adequate for current vehicle movement requirements. The output ofthe phase-error detector 116 is a DC voltage which is either positive, negative or zero, and of variable magnitude, depending on the phase relationship of the compared signals. The DC signal appears at terminal 0 117.  
 2. Bilateral Pulse-Generator 117 (FIG. 4).  
  The DC output voltage from the phase-error detector 116 is converted into a series of pulses whose frequency depends on the magnitude of the DC voltage. Depending on the polarity ofthe DC voltage, the pulses are segregated to output terminal 0 Sn (negative polarity) or output terminal 0 118p (positive polarity).  
  The DC input from terminal i 116 is integrated by operational amplifier ARZa to produce a signal ramp which will be either positive or negative, depending on the polarity of the voltage. The steepness of the ramp is determined by the magnitude of the voltage. Across integrating amplifier AR2a are connected two pairs of complementary transistors O3a-O4a and Q5aQ6a connected regeneratively to form an artificial fourlayer diode. When the voltage across either pair reaches the breakdown voltage, the pair conducts, discharging the integrating capacitor C9a. As a result, a positive or negative saw-tooth wave, whose polarity and frequency depend on the input voltage, is produced at the output ofoperational amplifier ARZa. The saw-tooth wave is differentiated by capacitor C 16a to produce a series of positive or negative pulses. These pulses are amplified through transistor 07a, and segregated by the pulse separator formed by transistors 08a and 09a. Transistor 08a is biased to be sensitive only to the positive pulses which thus appear as positive pulses at output terminal 0 11811. Transistor 09a is biased to be sensitive only to negative pulses which are then inverted by transistor Ql0a to appear as positive pulses at output terminal 0 118p. The frequency of the pulses depends on the input voltage magnitude, which is dependent on the magnitude of the phase difference between compared signals. The pulse frequency, in the examples shown, is on the order of 0 to 60 cycles per second.  
 3. Input or Short Gates 118a, l18n (FIG. 5)  
  As shown in FIG. 2, the phase-error detector 116 and the bilateral pulse generator 117 serve all of the local tracking-channels, being connected sequentially to the channels by input gates 118p and 118n, etc. and output gates 121, etc. The input gates 118p, 11811 are shown in FIG. 5. They are simultaneously gated by a signal at i to pass pulses from the bilateral pulse generator 117 to the adder-subtractor 119 and to the add and subtract counter storage 125 and 126. Besides the shared detector 116 and generator 117, each local tracking channel has connected to the reference oscillator 114 its own separate adder-subtractor 119, 219, etc. and tracking synthesizer 120, 220, etc., a construction of which is described in detail below for a single channel, the other channels having identical components.  
  4. Adder-subtractor 119 (FIG. 5). The addersubtractor 119 uses the pulses produced by bilateral pulse generator 117 to adjust the phase of the local 6.8 KC reference signal which is compared to the incoming signal in phase-error detector 116. The addersubtractor 119, accordingly, has inputs from the bilateral pulse generator 117 (through gates 118;), 11811), and it moreover has an input i 114 from the 2040 KC local reference oscillator 114. The output at terminal 0 is a 2040 KC signal with pulse additions corresponding in number to pulses at the input i 118p, and pulse deletions corresponding in number to pulses at input 2&#39; 118:1. This modified 2040 KC signal is then divided downwardly by a factor of 300 in the tracking synthesizer 120 to produce a phase-corrected 6.8 KC signal suitable for comparison in the phase-error detector 116.  
  The operation of the adder-subtractor 119 is as follows. For simplicity, the add and subtract functions will be taken separately. An add pulse through gate 118p triggers an Eccles-Jordan flip-flop 250, which opens gate 26a. The opening of gate Z611 permits the negative-going portion of the 2040 KC signal to trigger monostable multivibrator 28a to produce a 100 nanosecond delay. At the conclusion of this 100 nanosecond delay, monostable multivibrator 29a is triggered and produces a second 100 nanosecond delay pulse which is additively combined with the 2040 KC signal in gate 212a, the 2040 KC signal with inserted pulse then passing through gate 214a to output terminals 120. The signal which starts the first multivibrator Z80, also resets flip-flop ZSa through gate Z4a, to return the components to starting condition so that a second add pulse will produce the same result.  
  Subtract pulses through gate 1l8n trigger a separate flip-flop ZlSa which opens gate Z17a to permit the 2040 KC signal to trigger monostable multivibrator Zl5a. Monostable multivibrator ZlSa has a period of approximately 600 nanoseconds, which is slightly greater than the length of a single 2040 KC cycle. This 600 nanoseconds pulse is then used to inhibit gate Zl4a to interrupt the 2040 KC pulse train for this length of time, thereby eliminating one pulse. The pulse train, with deletion, appears at output 0 120. The pulse which triggers multivibrators ZlSa also resets flip-flop ZlSa through gate Z19a so that original conditions are again established and the process can repeat.  
  The signal at output terminal 0 120 is thus a 2040 KC signal which has its phase advanced 360 for each pulse at input 1&#39; 118p, and retarded 360 for each pulse at input i I18n.  
 5. Tracking Synthesizer 120 (FIGS. 1, 2).  
  Tracking synthesizer 120 counts down, or divides, the 2040 KC, phase-adjusted signal appearing at terminal 0 120 of the adder-subtractor 119, by a factor of 300. The resulting signal is the local 6.8 KC comparison signal which has its phase advanced or retarded l.2 for each pulse generated by the bilateral pulse gen erator 117 and inserted or deleted from the 2040 KC reference signal in adder-subtractor 119. This phase corrected 6.8 KC tracking signal is then commutatecl through gate 121 to be compared in phase-error detector 116 with the received signal from the station transmitting at that time. During the time that a local tracking channel is gated into the phase detecting circuit, errors of phase coincidence are being corrected by the servo mechanism which has been described. Because of the discrete nature of the phase correction signal, the reference 6.8 KC signal moves back and forth across the zero-error position by steps of 1.2, with the result that the actual RMS error is less by a factor of 2. During the time that a tracking channel is gated out of circuit with the received signal (9 out of every 10 seconds in ordinary Omega practice), the 6.8 KC comparison signal continues at the phase last established. The pulses produced by the bilateral pulse generator 117 are then interpreted as incremental changes of position of the receiver with respect to any one transmitter. By combining pulses from two tracking channels, it is possible to interpret the pulses as changes of position within the hyperbolic lanes of phase coincidence between the signals of the two transmitters so tracked. Since 300 pulses of one sense or would result in complete phase change of one cycle of the local 6.8 tracking signal, it follows that each single pulse represents H300 of a lane.  
  The numerals 1 to in FIGS. 3 to 5 represent in conventional manner the terminal numbers of the respective integrated circuit devices to which they are applied. The numerals 0 and 1 within the flip-flop symbols indicate the output states in conventional manner.  
  The nature and electrical connections of the elements of each of the circuit components contained in frame A (with the exception of the conventional counter at are clearly shown in FIGS. 3 to 5.  
 B. Commutator Circuitry Selection of the appropriate channel (119, 120 to 419, 420) is carried out by means of eight input gates 118p, 118n to 418p, 41814 and four output gates 121 to 421 in response to a gating pattern signal generated by timing function generator 115. Generator 115 produces a gate pattern which is synchronized with the incoming Omega envelope pattern by slewing circuitry comprising a manually controlled pulse generator 124 which, by manual selection, provides pulses to be added or subtracted in a synchronizing circuit 122. The synchronizing circuit 122 operates similarly to the adder-subtractor 119 to advance or retard the phase of a clock signal derived from the local reference oscillator 114. The clock signal, with its phase advanced or retarded for synchronization, operates shift registers in the timing function generator 115, which in turn controls the opening and closing of input gates 118p, ll8n to 418p, 418n (illustrated in FIG. 5) and output gates 121 to 421 (illustrated in FIG. 6).  
  In addition to providing a gating signal to commutate the local tracking channels, the timing function generator 115 provides a clock with 10 pps and a sequential, resetting signal for the add-and-subtract counter storage 125, 126, which will be explained in greater detail with reference to frame C.  
 1. Timing Function Generator (FIG. 7)  
  The timing function generator consists of a decade divider (FIG. 6) which provides a ten pulse-per-second signal, slewable in real time as described in the material that follows, a counter and decoder (FIG. 6a operating at a 10 Hz rate, and a shift register (FIG. 7) which provides long and short gates used to open and close gates 119p, 1181! to 418p, 418n (FIG. 5) and output gates 121 to 421 (FIG. 6).  
  Pulses from the decade divider (FIG. 6) are fed at a 10 Hz rate to i 115 of FIG. 6a, the basic time counter and decoder. Z16, Z12, Z8 and Z4 are binaries connected for a 10 count. The output of Z4 drives Z1, Z5, Z9, and Z13 which constitute a second, similarly connected counter. Selected outputs from the binary stages are combined in gates Z18 and Z to generate a zero pulse corresponding to the initiation of the internally generated Omega timing cycle, i.e. one pulse is generated for each 10 second interval.  
  The binary outputs are also combined thru several gates and collected in Z18 to generate 8 pulses during the 10 second interval, each one occuring at a time corresponding to the end of the short gate interval. These pulses at 0200 (FIG. 6a) are fed to the sampling counter and decoder (FIG. 6b) to i 200. The output of Z3d sets binary Z6 to enable gate Zl0c. Z10c and Zl0b pass the 10 Hz pulse train which appears at i 115 into Z4, Z8 and Z12, a three-stage binary counter. These stages count at a 10 Hz rate until a digital &#34;six is generated in Z3b which puts out a pulse actuating Z1, a one shot multivibrator whose output resets binaries Z4, Z8 and 212 to the zero state and in addition resets Z6, thereby inhibiting Z10c and stopping the 10 Hz input until the next pulse occurs at i 115. Outputs from the binary counters are combined in 27a and 23 a for a digital number corresponding to a one&#34; and a *five&#34; respectively which set and reset binary Z2. The output of binary Z2 corresponds timewise to the short gate signals previously mentioned.  
  Outputs from the binary counters are further combined in Z70 for a binary number three. This three&#34; is combined with the Hz clock in 210a to provide a synchronous pulse at the exact time to initiate the long gates previously mentioned. This pulse line is fed out through 210d to connection 0202 to the long-gate shift register (FIGS. 6 and 7). Other digital numbers are decoded in 213a, Z13b, Zllb, Z110 and Z1 la. Two of these are combined with long gates from the long gate shift register fed in on Z14b, pin i 203 and 2140, pin 1&#39; 204 to generate discrete pulses between the third and fourth Omega transmission segments which are used along with the Zero pulse previously mentioned to initiate count out operation in 125 &amp; 126, 225 &amp; 226, and 325 and 326 of FIG. 2 at discrete intervals during the IQ second timing cycle.  
  A reset pulse corresponding to the zero&#34; pulse generated in the basic time counter and decoder feeds the long gate shift register (FIGS. 6 and 7) and resets the shift register comprising Z8, Z4, Z3, Z7, Z6, Z2, Z1, and Z5, once every 10 second interval. The drive pulse, corresponding to the binary 3&#34; described in the sampling counter and decoder shifts the register one stage for each input, thereby generating a pulse on each of the eight buffered output lines provided by 212b, 212d, Z1 lb, Z150, 215d, Z140, 214d and Z1 la in proper time sequence. These pulses are the long gates referred to earlier.  
  The output of each stage of the shift register is in addition fed to gates Z120, Z110, 215b, 210b, Z100, Z14b, 29b, and Z90. During each long gate signal, these gates are enabled and act to separate the short gate signals heretofore developed on one line as described in the sampling counter and decoder and to provide separate short gate outputs as required to operate gates 121 to 421 (FIG. 6).  
 2. Pulse Generator 124 (FIG. 6).  
  Pulse generator 124 is a conventional relaxation oscillator employing a unijunction transistor Qlb. The pulse generator 124 operates only when switch Slb is closed manually to bias the circuit into oscillation.  
  By means of switch 82b, the output of pulse generator 124 can be connected either to time-advancing input i 124p or to time-retarding input i 124n of the synchronizing circuit 124.  
 3. Synchronizing Circuit 122 (FIG. 6)  
  Synchronizing circuit 122 has an input 1 1145 which accepts a 17 KC reference signal derived from the local oscillator 114. This 17 KC signal is divided by I70 in divider 122d to produce a pulse train of lOO pps which, as modified in a manner now to be explained, appears at output terminal 0 115 to run the shift registers in the timing function generator 115. The I00 pps pulse train and the resulting gate pattern is slowed down or hurried up by the addition or deletion of pulses from pulse generator 124 which pulses are manually selected to be applied either to the time advancing input i 124p or the time-retarding input i 124n. A pulse appearing at input 1&#39; 124p is treated as follows:  
  A pulse appearing at l24p sets flip-flops Z8b enabling flip-flop 2101) thru gates which are enabled by either 24b or Zb. The next I00 pps signal occurring at the output of Zlb operates to set flip-flop 21012. The output of 21% enables gate 26b to pass one pps-pulse to initiate two delay one -shot multiocrotors Z181: and Z191). The output of 21% is delayed by 21805 until approximately midway between the first and second sequential 100 pps outputs from Zlb at which time it generates a narrow pulse which is inserted in the 100 pps train by action of gate 22b.  
  The change in state of flip-flop 2101; is led to set flipflop 29b which inhibits gate 25b through gates 24b or 21519. The second sequential 100 pps output from Alb resets 21% to its original state inhibiting gate 26b and returning the circuit to rest until the next pulse on line 0 124p changes the state of flip-flop 28b.  
  Similarly, a pulse appearing at the retard input i 12411 is treated as follows:  
  A pulse appearing at 124a sets flip-flop Z12b, thus enabling flip-flop Z14b thru gates Z176, which is in turn enabled by either gate Z1 lb or Z16b. The next following I00 pps at the output of 2212 sets flip-flop Z14b, thereby inhibiting gate 23b, and changing the state of 22% to inhibit gate Z176 thru either gate Z116 or gate Zl6b. The second sequential 100 pps pulse at the output of Z2b resets Z116 which enables gate 23b and the circuit is at rest condition, having deleted one pulse in the 100 pps train appearing at the output of gate 23b.  
  Correspondence between the station transmission envelope pattern (a, b, c, d of FIG. 1) and the gate pattern of timing function generator is achieved by the foregoing synchronization circuit. This circuit essentially serves to phase shift the 10-second cycle of the timing function generators gating pattern, relative to the time base established by the reference oscillator 114. This is accomplished by inserting extra pulses in. or deleting some of the normal pulses from, the 100 pps train derived from the reference oscillator 114. Since the reference oscillator 114 is phase-locked to one of the received Omega signals (see description of frame E below), the gating pattern can be made to coincide, within 1] 100 of a second, to the Omega signal pattern as received.  
  Synchronism can be observed and verified with oscilloscope 133 (FIG. 2). The oscilloscope 133 provides a dual trace for comparison purposes, i.e., one trace being provided by the envelope of the received Omega signal (developed in envelope detector 132) and the other trace being provided by the gate pattern of the timing function generator 115 which also provides the sweep. By comparing the two traces, visual observation of synchronism is possible. Other means for observing and verifying synchronization are available: For example, a pair of lights energized respectively by the gating pattern and by the received Omega signal envelope will show synchronizationIOr, by way of another example, a meter comparing one channel&#39;s envelope with the gate pattern therefor will show synchronism.  
  A stop-start switch 83b permits the clock pulse-train, fed to timing function generator 115, to be interrupted. When on stop,&#34; the switch also resets at input i 83b (FIG. 7) the shift registers to zero in the timing function generator. Thus, switching switch 83b, set to start, will initiate the gate sequence on the next clock pulse.  
 C. Digital Position Display The pulses which are inserted or deleted to correct phase in the local tracking channels provide the information used by the circuitry of frame C for a numberical readout of position in terms of lanes and centilanes. These pulses are stored in a counter-register as they are generated, and then periodically transferred to the electro-mechanical counters 127.5, 227.5 or 327.5. Each electro-mechanical counter is adapted to display decimally the position of the receiver, expressed in lanes and centilanes, in relation to a pair of transmitting stations. Usual Omega practice assigns a number to each of the hyperbolic lines of phase coincidence between a pair of transmitting stations and identifies the interline regions as lanes. A centilane is, accordingly, a distance equal to one hundredth of the distance between the two lines which the receiver identifies. After the lane and the centilane count is initially set into one of the electro-mechanical counters, such as 127.5, a change of position of the receiver, producing phasecorrective pulses in generator 117, is indicated in the following manner. For simplicity, there will be described only the circuitry necessary for handling two transmitting stations, such as a, 10b (FIGS. 1, 1 a) which comprises counter-storage 125 and 126, comparator and driver 127, and electro-mechanical counter 127.5. Circuitry identical to that of 127.5 is associated with counters 227.5 and 327.5, which may, for example, display position with respect to transmitting stations 10b, 100 and 10d, respectively.  
  Operation of the circuitry blocks 125, 126 and 127 is more easily understood by first considering the arith metic operations to be performed therein. Briefly, block 125 adds pulses representing positive phase changes in one channel to pulses representing negative phase changes in a second channel. Block 126 adds pulses representing negative phase change in the one channel to pulses representing positive phase change in the second channel. The pulse total of block 125 is applied to the electro-mechanical counter 127.5 in a sense opposite to the pulse total from block 126 to obtain the difference between the two numbers of total pulses. This difference represents, in pulse terms normalized to centilanes, the net change of phase at the receiver of the one channel&#39;s transmitting station with respect to the second channels transmitting station.  
 1. Counter-storage 125 (FIG. 8).  
  The storage circuit 125 of FIG. 8 has inputs i 118;) and i 2l8n from the respective short gates, pulses from which are added in gate Z10. The pulses from the two inputs never coincide to give a false count, since the gates 118p and 218n, associated with different channels, are opened sequentially and never simultaneously. As noted above, each pulse inserted or deleted to correct phase represents [/300 of a cycle of phase change. To obtain a signal whose pulses each represent one centilane, the input pulses are therefore divided by three in the circuit formed by Z and Z30. These pulses in turn are applied to a binary count-up register formed by elements Z40, Z50, Z60 and Z70, which register has a counting capacity of l6.  
  The storage circuit 125 further has an input 1&#39; 222 from the synchronizing circuit 122, as mentioned above, which feeds its 100 pps pulse train to a transfer pulse generator ll5b and a clock pulse generator 115a, both of which are actually part of timing function generator 115 referred to above. The transfer pulse generator 1151: delivers a pulse to the pairs of storage circuits 125, 126; 225, 226; 325, 326 to instigate the readout process. The pulses are delivered to the pair in sequence to reduce the power requirements of the receiver, but they are sent simultaneously to both storage circuits forming one pair, such as 125, 126. The clock pulse generator a divides the I00 pps signal by l0 to produce a 10 pps clock-pulse train.  
  When a transfer pulse is delivered to the storage circuit 125, it opens gates 290 through Z to transfer the count in the count-up register to a second register comprised of Z190 through Z220. As the circuit connections show, the transfer is of the conjugate of the number of accumulated pulses in the count-up register. For example, if the count-up register contained the binary number OOl 1, this would be transferred as its conjugate N00 to the count-down register.  
  The transfer pulse, in addition to causing the conjugate transfer of the stored-up number of pulses, also triggers a delay component Z250 which resets the count-up register to 0000 to begin counting anew.  
  The transfer pulse furthermore latches Z230 into a state enabling gate Z180 to pass to the count-down register the 5 pps signal derived by dividing the 10 pps clock signal from 1150 in binary Z170. The 5 pps signal through gate Z180 at o 127 passes to comparator and coil driver output 127 (FIG. 9) and also is applied to the count-down register. When enough pulses have been applied to the count-down register to increase the count (from the transferred conjugate value) to 1111, the gate 2240 is activated and unlatched to disable Z180 so that no more pulses will pass to the comparator and coil driver 127 until the next transfer pulse from 11511 is applied.  
  From the foregoing it is readily seen that the storage and count-out circuit 125 functions broadly as follows. The input pulses are divided by three and stored in a count-up register until a transfer pulse causes the count to be transferred as its conjugate to a count-down register. The count-up register is immediately reset so that it will keep counting pulses generated in 117. The transfer pulse also enables a cloclepulse train to deplete the count-down register, at the end of which the circuitry is reset to its initial condition.  
  FIG. 9 is a timing diagram depicting certain wave forms during a typical l0 second interval of operation of storage and count-out 125, FIG. 8, circuit. The diagram shows five pulses entering this circuit at input 1&#39; 118p during its short gate and four pulses entering the circuit at input i 218n during its short gate. This total of nine pulses is divided by three, as can be seen at the Z30 output wave form. This number is counted into the register composed of Z40, Z50, Z60, and Z70 as shown by the output wave form of FIG. 9. At the end of the ten second interval a transfer pulse from reset generator l15b shifts the conjugate of this count into the register comprised of Z190, Z200, Z210, and Z220. In this embodiment, in which the total pulse input is nine in the 10 second interval, the count-up register reads OOl l (or 3) and the transfer to the count-down register is made as 1100. Immediately following transfer, the count-up register is reset to 0000 by a pulse at the output of Z250, to make it ready to resume counting during the next interval. Binary Z accepts l0 pps and provides the 5 pps signal which appears at the output of Z when that device is enabled by a change of state at the output of Z240. Z240 assumes one state enabling Z180 whenever any count not 1 l l l is present in the count-down register. The output of the enabled Z180 counts out the count-down register and provides the signal ultimately fed to terminal 0 127 and to the