US2526287A

US2526287A - Radio navigation system

Info

Publication number: US2526287A
Application number: US638387A
Authority: US
Inventors: Stuart W Seeley
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1945-12-29
Filing date: 1945-12-29
Publication date: 1950-10-17
Anticipated expiration: 1967-10-17

Description

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Oct. 17, 1950 s. w. sEELEY amo mvmmon SYSTEM wm 9 2 mm .M D Il .m vm i F Patented Oct. 17, 1950y RADIO NAVIGATION SYSTEM Stuart W. Seeley, Roslyn Heights, N; Y., assignor to Radio Corporation of America, a corporation of Delaware Application December 29, 1945, Serial No. 638,387

My invention relates to position determining systems and more particularly to pulse-echo radio systems of the type that transmit radio pulses from an aircraft, a ship or the like to a pair of repeating or reflecting ground stations, and then receive said pulses from the ground stations to determine the distances to the two ground stations. Thus, the position of the transmitter carrying craft may be determined from the two pulse-echo determined distances and from the known positions of the two ground stations.

The present invention is an improvement over the system described in my copending application Serial No. 381,020, led February 28, 1941, and entitled Position Determining Systems, now Patent No. 2,405,239. One specific use for. the system described hereinafter is for blind bombing of a target. In addition to determining the position of the bomb carrying aircraft, my improved system also gives the rate at which the aircraft is moving away from one of the ground stations (referred to as the rate station) ,and this rate information may be fed into a bombing computer. f'

An object of the invention is to provide an improved method of and means for determining the position of a craft or other mobile unit.

Another object of the invention is to provide an improved method of and means for bombing a target that is not visible.

Another object of the invention is to provide an improved method of and means for determining the rate at which a craft or other mobile unit is moving away from or toward a ground station.

Still another object of the invention is to provide an improved method of and means for producing marker and pulse indications in a position determining system of the above-mentioned type.

Other objects, features and advantages of the invention will be apparent from the Ifollowing description taken in connection with the accompanying drawing in which Figures 1a and 1b, which are to be placed side by side, are a block diagram of a position determining system embodying the invention,

Figure 2 is a circuit diagram of the quadrature networks and goniometer phase shifters shown in Fig. la.

Figure 3 is a view illustrating the marker and ground station pulses as they appear on the end of the cathode ray indicator tube shown in Fig. lb,

Figure 4 is a group of graphs illustrating the selection of the transmitted pulses.

24 claims. (ci. 343-15) lshifter as explained hereinafter.

Figure 5 is a circuit diagram of a pulse selecting circuit,

Figure 6 is a. group of graphs illustrating the selection of the marker pulses,.

Figures 7, 8 and 9 are groups of graphs that are referred to in explaining the operation of the system when the indicator is switched to the range positions for miles, 10 miles and 1 mile,

respectively,

Figure 10 is a diagram that is referred to in explaining a method of operation for/preventing station interference,

Figure 11` is a diagrammatic showing of a portion of a computer illustrating how it may be combined with the system shown in Figs. la and 1b, and

Figure l2 is a view of a differential unit that may be employed in the apparatus of Fig. v11.

In the several figures, similar parts are indicated by similar reference characters.

The operation of the system shown in Figs. `1a and 1b .is the same in principle as that of the system described in my above-identified pending application. This principle is vas follows, assuming that the system is to be used for bombing a certain target: The rate pulses transmitted from the aircraft to the rate ground station are delayed with respect to a marker pulse before being radiated by an amount such that when each rate pulse returns to the aircraft it coincides with a marker pulse. T he drift pulses are transmitted similarly to the drift ground station. In said pending application the system is operated so that this coincidence of pulses occurs at the instant the target is reached, the correct pulse delay being preset and remaining unchanged during a bombing run. y

According to the present invention the rate pulse delay Iis changed continuously during a bombing run lto maintain coincidence of the rate pulse and the marker ypulse indications on the indicator tube screen. 'I'his continuously changing delay of the rate pulse is obtained by continuously rotating a phase shifting device which, as described hereinafter, comprises three goniometer phase Shifters which arey geared. to each other by gears having a l0 to' 1 ratio. The instant that the target'is reached may be determined by means of a mileage counter geared to a phase shifter shaft. However, for bombing it is preferred .to couple a computer to the phase It will be evident that the rate of movement of the aircraft from the rate station is given by the rate of -rotation of the phase shifter shaft so long as the rate pulse and marker pulse coincidence is maintained.

Referring to Figs. 1a and 1b, both the transmitted pulses and the marker pulses are derived from a crystal controlled oscillator I operating at 93 kilocycles per second. The 93 kc. sine wave output of oscillator I0 has its frequency divided by 10 by a frequency divider II to obtain a 9.3 kc. sine wave signal. The 9.3 kc. signal has its frequency divided by 10 by a frequency divider I2 to obtain a 0.93 kc. sine wave signal.

Rate pulse phase shift and selection The outputs of the frequency dividers I6, II and i2 are supplied over conductors I3, I4 and I6 to quadrature networks I1, I3 and I9, respectively. The networks I1, I3 and I3 supply 93 kc., 9.3 kc. and 0.93 kc. signals in quadrature relation over conductors 2|, '22 and 23 to goniometer

type phase shifters

24, 26 and 21, respectively, which function to delay the transmitted rate pulse.

The 93 kc. output of phase shifter 24 is supplied through conductors 9, a cathode follower tube 28 and a conductor 25 to a pulse selector circuit 29. The 9.3 kc. and 0.93 kc. outputs of

phase shifters

26 and 21 are supplied through conductors I6 and 20 and pulse shaping circuits 3| and 32, respectively, and over conductors 30 and 36 to the pulse selector circuit 29. In this way, as described more fully below, a half cycle or fractional portion of the 93 kc. wave is selected periodically to produce an output pulse at output lead 40 of the pulse selector 29 that recurs at the rate of 0.93 kc. per second. This selected pulse is passed through a pulse shaper 33 to obtain a rate pulse of the proper width for modulating the radio transmitter 34. The pulse from the shaping circuit 33 is supplied periodically through a switch 36 and an amplifier 31 to the transmitter 34.

Fig; 4 illustrates the method of pulse selection which is similar to that describedV and claimed in my above-identied application. The outputs of the cathode follower 28 and the pulse shapers 3| and 32 are shown by the

graphs

38, 39 and 4|, respectively, in Fig 4. It will be seen that graphs 39 and 4I represent pulses recurring at 9.3 kc. and 0.93 kc. per second. To obtain the pulses 39 and 4'I, the pulse shaping circuits 3| and 32 may each comprise a. limiter tube followed first by a differentiating circuit and then by a clipping circuit. Such wave shaping circuits are so Well known in the art that they need not be described in detail.

Fig. shows one suitable pulse selector circuit which comprises a multi-grid vacuum tube 42 having potentials of such value applied to three of the grids that signal must be applied to all three grids before the tube passes anode current. Therefore, a half cycle of the 93 kc. signal is passed by the pulse selector 29 each time there is coincidence of the 9.3 kc. pulses 39, the 0.93 kc. pulses 4I and said 93 kc. half cycles. In the example illustrated, the negative biases on the grids are obtained by the well known grid leak biasing action, the grids being driven positive by the applied signals whereby there is a periodic flow of grid current. However, the grid biases may be obtained from batteries or voltage dividers, if preferred.

The quadrature networks and the phase shifters shown in Fig. 1a and Fig. 2 are designed the same as those described and claimed in my 4 copending applications Serial No. 548,183, now Patent No. 2,450,616, issued October 5, 1948, tiled August 5, 1944, and Serial No. 547,255. now Patent No. 2,496,920, issued February 7, 1950, filed July 29, 1944, respectively, and entitled, respectively, Electrical Networks for Phase Shifters" and Phase Shifters." This portion of the system will be described in some detaill hereinafter.

Drift pulse phase shift and selection Reference will now be made to the phase shifters and the pulse selector for obtaining the drift pulse for transmission to the drift ground station. It will be understood that the rate and drift pulses are transmitted alternately atdifferent carrier frequencies such as frequencies fI and f2, the switch 36 being operated to engage its upper and lower contact points alternately for this purpose. A switch 4'0 at the transmitter 34 is operated in synchronism with the switch 36 for changing the carrier wave frequency.

The quadrature networks I1, I8 and I9 supply 93 kc., 9.3 kc. and 0.93 kc. sine wave signals in quadrature relation over conductors 5|, 52' and 53 to the goniometer

type phase shifters

64, 66 and 61, respectively. The 93 kc. output of phase shifter 64 is supplied through conductors 68, a cathode follower tube 69 and a conductor 6I to a pulse selector circuit 62 that is similar tn the pulse selector 29.

The 9.3 kc. and 0.93 kc. signals from the

phase shifters

56 and 51 are supplied, respectively, to the pulse selector 62 through conductors 83, a pulse shaper 64 and a conductor 66, and through conductors 61, a pulse shaper 38 and a conductor 69. Thus, a drift station pulse recurring at a repetition rate of 0.93 kc. per second is obtained at the output lead 1| of the pulse selector 62 in the same way that the rate station pulse is obtained at the lead 40. The drift pulse is made of the desired width by a pulse Shaper 12 and supplied to the lower contact point of the switch 36 for periodically pulse modulating the radio transmitter 34.

Phase shifter gearing The three

phase shifters

24, 26 and 21 for the rate pulse delay and selection are geared to each other with 10 to 1 gear ratios so that the rotorof the phase shifter 24 makes 100 rotations for every 10 rotations of the rotor of phase shifter 26 and for every 1 rotation of the phaseV shifter 21. These gear ratios correspond t-o the ratios of the frequencies of the signals applied to the phase shifters.

As illustrated in Fig. la, the rotors of the

phase shifters

24, 28 and 21 may be rotated by turning a crank 13. The phase shifter 24 is driven through the gears 14 and 16, and 'I1 and 18. The phase shifter 26 is driven through the l to 10 ratio gears 19 and 8|, and the 1 to 1 ratio gears 92 and 83. The phase shifter 21 is driven through the 1 to 10 ratio gears 19 and 8| and through the 1 to 10 ratio gears 84' and 86.

A mileage counter 81 which is connected by bevel gears 88 to the phase shifters indicates the mileage in units, tenths and hundredths.

For more rapid initial setting of the geared phase shifters, means comprising a knob 89 and a detent 9| are provided for rotating the phase shifter 21 Without rotating the

other phase shifters

26 and 24. Only the phase shifter 21 is rotated by the knob 89 when the knob is pulled away from the panel 92 since this dis-l The quadrature networks Referring to FigureA 2, two resistive elements |0I, |03 and two reactive elements |05, |01 are connected to form a Wheatstone bridge. The resistive elements |0|, |03 are in opposite arms of the bridge as are the reactive elements |05, |01. A second Wheatstone bridge is formed with similar resistive arms |09, |`|I and similar reactive arms |I3, ||1. As in the case of the iirst bridge, the resistive arms |09, III are opposed asare the reactive arms II'3, I|1 and the four reactive elements are of similar sign. The two bridges are connected in series by forming a common connection I|9 at the junction of the arms |03, |01 of the first bridge andthe junction of the arms |09, ||3 of the second bridge. The input terminals of -the two bridges are supplied from the conductors I3.

The rst output terminals |21 and |29 of the network are formed by the junction of arms l0| and |01 and by the junction ci the arms |03 and |05 of the first bridge.- The other pair of output terminals |3I, |33 are formed. by the .junction of the arms |09 and |'|1 and by the junction of the arms III and ||3 of the second bridge. These four terminals |21, |29, |3I, |33 become the source of quadrature phase currents which may be applied for any desired purpose. In the present system, two of the field coils |35, |31 of the goniometer phase shifter 24 are con nected across the terminals I21-I3I and |21- |29, respectively. The eld coils |4||43 of the goniometer phase shifter 54 are yconnected across the terminals |29--I33 and |33|3|, respectively. The rotor of the rst goniometer is represented as a pick-up coil |41 while the rotor of the second goniometer is represented as a pick-up coil |49. 'I'he pick-up coils each represent sources of voltage having a phase which may be adjusted through any desired angular shift up to 360 degrees per complete rotation oi the pick-up coil. i v

To provide the best results the impedance of all arms of the two bridges should be made numerically equal. By way of example, where the signal from leads I3 has a frequency of 93 kilocycles, the several resistive elements |0I, |03, |09 and may be 855 ohms whilel the several reactive elements |05, |01, |I3 and |'|1 may have capacities of 2000 micro-microfarads. These capacities at 93 kilocycles have a reactance of approximately 855 ohms. If the two bridges are thus arranged, it can be shown mathematically that the currents in the several output connections |21-|29, I29-I33, |33|3|', and |3I`|21 will be in quadrature with each other and will continue to be in quadrature substantially independent of the resistances or impedances connected across the output terminals provided only that those resistances or impedances remain equal to each other. f i

If the network is connected to pairs of goniometers whose inductive reactance is numerically equal to the impedance oi the other arms as shown in Figure 2, the phasey of the goniometer primary currents will be completely independent of ambient temperature changes. This is lan important feature of the network in view of the fact that the goniometer eld coils (usually wound of copper wire) have a substantial amount of resistance. Since an ordinary goniometerv connection to a. conventional phase shifter would be inuenced by the eilect of temperature changes in the goniometer coil, it follows that the symmetrical arrangement-of the present network offers great'advantages. Likewise, if the inductance of each of the windings is made equal in ohms to each of the eight arms of the 4electrical bridge network, the phases oi' the currents through the goniometer field coils o r stators |31, etc. maintain xed relations to the phase lof the driving voltage from the leads |3 in the presence of wide variations of ambient temperature. f

The goniometer eld coils |35, |31, I'4I and |43 have connected in series with them resistors |5I, |52, |53 and |54, respectively, these resistors be-A ing of like value.

The quadrature networks I8 and I9 which are supplied with 9.3 kc. and 0.93 kc. signals from the leads I4 and I6, respectively, are the same as the network I1 except for the fact that the circuit constants are diiferent so as to conform to the frequencies of the applied signals. However, in network I8 an additional resistor |56 of 100,000 ohms resistance is included for supplying a 9.3 kc. signal adjustable in phase over a conductor |55, and in network I9 additional resistors |51 and |58 of 500,000 ohms each are included for supplying 0.93 kc. signals adjustable in phase over conductors |59 andV |6|,'respectively.

Circular cathode ray sweep In Fig. 1b the cathode ray indicator tube is shown at |62. A circular sweep of the cathode ray is obtained by applying voltages in quadrature from amplifiers |63 and |64 to two pairs of deecting plates |66 and |61, respectively. A radial deflecting electrode |66 has the received rate anddrift pulses and the marker pulses applied thereto from a conductor |65 so that they appear on the screen |60 of the tube |62 als shown in Fig. 3 when the three pulses are in coincidence at their leading edges. It will be noted/ithat the polarity of the drift pulse is reversedwith respect to the rate and marker pulses. tube |62 is provided with a cathode |69, a, control grid |1| and the usual .anode electrodes (not shown) Sine wave voltages in quadrature are supplied to the input leads |12 and |13 of the ampliiiers I 53 and |64, respectively, by way of al pair of witches |14 and |16. Each switch has three positions which are shown as positions UI, II and III-and which correspond to the mile scale, the 10 mile scale 'and thepl mile scale on th indicator tube screen |60.

The indicatorcircular sweep are taken off resistors in series with the goniometer stator coils.

Production of marker pulses The marker pulse selection is similar to the previously described rate and drift pulse selection, the principal difference being that the goniometer type phase shifters are not employed. Instead, except for a zero phase adjustment, the necessary phase adjustments are made at the quadrature networks I8 and I9.

Referring to Figs. 1a and 1b, sine wave signal of 93 kc. is supplied from the crystal oscillator I over a conductor |86 and through a zero set phase shifter |81 to a marker pulse selector |88 (Fig, lb). The phase shifter |81 is a resistorcapacitor network. The marker pulse selector |88 may be the same as the rate pulse selector 29.

Sine wave signal of 9.3 kc. is supplied from the quadrature network I8 over a conductor |55 to a pulse Shaper |89, a suitable phase adjustment being provided as indicated by the block |9| (Fig. 1b) As shown in Fig. 2, the phase adjusting device |9| may be the resistor |56 provided in the network I8 and having an adjustable tap thereon. The output of the shaper |89 is a rectangular pulse of microseconds duration, indicated at 2, which recurs at the 9.3 kc. repetition rate. This pulse is supplied to the pulse selector |88.

Sine wave signal of 0.93 kc. is supplied from the quadrature network I9 over a, conductor |59 to a pulse Shaper |92, a suitable phase adjustment being provided as indicated by the block |93. As shown in Fig. 2, the phase adjusting device |93 may be the resistor |51 provided in the network I9 and having an adjustable tap thereon. The output of the shaper |92 is a rectangular pulse of 100 microseconds duration, indicated at 3, which recurs at the 0.93 repetition rate. This pulse is supplied to the pulse selector |88 through a switch SI when it is in the No. I or 100 mile scale position. It may be noted that all switches which are indicated in the drawing as having switch positions I, II and III are preferably ganged for operation from a single knob.

Fig. 6 shows the time relation of the signals applied to the pulse selector |88 for the different switch positions. It will be seen that in the No. I position a half cycle portion of the 93 kc. wave. indicated at I, is selected by the

pulses

2 and 3 to produce a marker pulse 5 that recurs at the 0.93 kc. repetition rate. In the example illustrated, the pulse 5 has been narrowed by a differentiating transformer or circuit |94 (Fig. 1b). The regular marker pulses 5 and the offset marker pulses described hereinafter are supplied from the pulse selector |88 through the differentiating circuit |94 to a marker pulse amplifier |95, and from amplifier |95 over a conductor |65 to the radial deflecting electrode |68.

In switch positions II and III the marker pulse 5'is not produced but instead an offset marker pulse 6 is produced for a reason explained hereinafter. With the switch SI in either position II or III a rectangular pulse 4 of 100 microseconds duration is supplied to the pulse selector |88 in place of the pulse 3.

The pulse 4 is obtained by supplying sine Wave signal of 0.93 kc. from the quadrature network I9 over a conductor |6| to a pulse Shaper |96, a phase shift adjustment being provided as indicated by the block |91. As sho-wn in Fig. 2, the phase shifting device |91 may be the resistor |58 8 provided in the network I9 and having an adjustable tap thereon.

Referring again to the graphs of Fig. 6, it will be seen that in switch positions II and III the

rectangular pulses

2 and 4 select a, half cycle portion ofthe 93 kc. wave to produce the marker pulse 6 which is offset" with respect to the timing of the regular marker pulse 5, that is, it occurs 107.5 microseconds later. Thus, the marker pulse 5 occurs 10 circular sweeps later than the marker pulse 5 when the 1 mile scale (position III) is being used and 1 circular sweep later than the marker pulse 5 when the 10 mile scale (position II) is being used.

Reason for oset marker pulsev not of much importance for the mile scale (position I) as only a rough adjustment` of coincidence is required. Therefore, the regular marker pulse 5 is utilized in position I.

For the 10 mile and 1 mile scales, however, separate marker and rate pulse indications must appear on the indicator tube screen |60 as shown in Fig. 3. The use of the offset marker pulse 6 makes this possible Ibecause, as shown by the graphs in Figs. 8 and 9, the rate pulse 'I'RI and the offset marker pulse 6 do not occur simultaneously. Yet, the pulses TRI and 6 have the same time relation with respect to the circular sweep of the cathode ray and are viewed simultaneously by the operator due to persistence of phosphorescence of the screen or persistence of vision or both.

Circle blanking In the 10 mile and 1 mile scale positions (positions II and III) the cathode ray makes 10 and 100 circular sweeps, respectively, on the screen |60 per marker pulse unless the ray is blanked during some of the sweeps. Such blankingI referred to as circle blanking. isprovided for .positions II and III as otherwise the circular trace would be too bright as compared with the marker indication or pip. Circleblanking for the 100 mile scale is unnecessary as there is only one circular sweep per marker pulse, this fact being illustratedin Fig. '1.

The graphs of Fig. 8 show how circle blanking is applied for the 10 mile range. First, it should be noted that, in practice, the cathode-ray tube |62 isbiased beyond beam current cut-off so that the cathode ray does not strike the screen |60 unless a positive pulse is being applied to the grid I1I by way of a conductor 20|. Thus, the

positive pulses

3 and 4 which, for position II, are fed into the blanking circuit for circle blanking control are referred to as circle lighting pulses. The biasing source as well as a conventional directcurrent setter circuit or brightness equalizer circuit are represented by a block `202. As shown in Fig. 8, the pulse 3 occurs during the occurrence of the first circular sweep and during the occurrence of the rate and drift pulses TRI and TDI, respectively. The pulse 4 occurs during the second circular sweep and during the occurrence of 9 the oiset marker pulse 6. In this switch position II the regular marker pulse is not produced.

Referring now to Fig. 1b and assuming the switches SI, S2, etc. are in the No. II position, it will be seen that the pulse 3 is supplied over a conductor 203 and through the switch S2 to a circle-lighting pulse selector 204 and that the pulse 4 is supplied over a conductor 206 and through the switch S4 to a second circle-lighting pulse selector 201. The

pulse selectors

204 and 201 are similar to the rate pulse selector 20 except that each selector tube has only two grids, that have signal applied thereto. In position II, each of the selectors 200 and 201 has one of these two grids grounded by way of the switch S3. The bias adjustments are such that under these conditions the

pulses

3 and 4 pass through

selectors

204 and 201, respectively, and are supplied to an amplier 208. The amplied circle-lighting pulses are supplied from the amplifier 208 over conductors 209 and 20| to the grid |1| of the indicator tube. Thus, the

pulses

3 and 4 light up two successive circular sweeps for the mile scale as illustrated in Fig. 8.

Assuming next that the switches Sl, S2, etc. are in the No. III or 1 mile scale position, the pulses 2 of 10 microseconds duration are supplied through a conductor 2 and the switch S3 to the pulse selector 205. At the same time thepulse 3 is supplied through the conductor 203 and the switch S2 to the pulse selector 204. The time relation of the pulses is shown in Fig. 9 where the first occurring pulse 2 is identied as 2a. Thus the pulse 2a is supplied as a circle-lighting pulse to the amplifier 200.

Similarly, the pulse 2 is supplied through the conductor 2l I, the switch S3 and a conductor 2 l2 to the pulse selector 201. The pulse 4 is supplied through the conductor 206 and the switch S4 to the pulse selector 201. Thus, as shown in Fig. 9, the second occurring pulse 2 indicated at 2b is supplied as a circle-lighting pulse to the ampliiler 208. It will be evident from an inspection of the graphs in Fig. 9 that the pulse 2a unblocks the cathode ray for one circular sweep during the time the received rate and drift pulses TRI and 'I'DI are appearing on the radial defiecting electrode |68 of the indicator tube. Also, the second occurring 10 ps. pulse 2b unblocks the cathode ray for one circular sweep 107.5 microseconds or 10 circular sweeps later and during the time the offset marker pulsef6 appears on the electrode |68. Again, the regular marker .pulse 5 is not produced.

Since the offset marker pulse 6 is in the same time relation to the circular sweep as the regular marker pulse 5 would beif produced, the desired marker pulse indication or pip appears on the indicator screen |60 and, as in the case of-the 10 mile scale, this marker pulse pip and the rate pulse indication or pip appear as separate and distinct marks as shown in Fig. 3 at the time the rate pulse is being adjusted to exact coincidence with the marker pulse.

Reception of rate and drift pulses The rate pulses TRI, TR2, etc. and the drift pulses TDI, TD2, etc. (Fig. 7), after retransmission from the rate and drift ground stations, are received at the aircraft receiver 2|3 (Fig. 1b) The rate and drift pulses are retransmitted from the rate and drift ground stations at the same carrier wave frequency. The rate and drift ground stations, for example, receive the aircraft transmitter rate and drift pulses on carrier-Wave frequencies fi and f2, respectively, andl both stations retransmit to the aircraft on a frequency f3.

The rate and drift pulses are supplied from the receiver 2|3 to 'a pulse inverter tube 2I4 and to a cathode follower tube 2I6. The outputs of the tubes 2|4 and 2|6 are supplied alternately through a switch 2|1, an amplier 2I8 and the conductor to the radial deflecting electrode |08 of the indicator tube |62.

The switch 2|1 is operated in synchronism with the transmitter switch 36 (Fig. 1a) so that the cathode follower 2|6 supplies signal to amplifier 2|8 when rate pulses are being transmitted to and retransmitted from the rate ground station, and so that the pulse inverter 2|4 supplies signal to the amplifier 2|B when drift pulses are being transmitted to and retransmitted from the drift ground station. In this way the rate pulse pip is produced outward from the circular sweep and the drift pulse pip is produced inward `from the circular sweep as shown in Fig. 3.

Receiver blanlcing In the 10 mile and 1 mile scale positions II and III, respectively, noise signal from the receiver 2 i3 is prevented from passing through the inverter and cathode followertubes'2l4 and 2|6 during the occurrence of the offset marker pulses 6 so that there will be no noise signal appearing on the radial deflecting electrode |68 to obscure or distort the marker pulse pip. This is accomplished by applying blanking pulses to the screen f grids, for example, of the inverting and cathode follower tubes 2|4 and 2|6. The pulse 4 is used Transmitter blanking At the aircraft, the transmitted rate and drift pulses will feed into the receiver 2|3 and appear on the indicator screen unless they are blanked out. They are blanked out by supplying some of the signal from the switch 36 (Fig. 1a) over a s conductor 222 to an ampliler 223 (Fig. 1b). From the amplier 223 negative pulses are supplied through a conductor 224, a switch 226 and the conductor 20| to the grid of the indicator tube |62. The switch'226 may be opened to allow the transmitted pulses to appear on the -indicator screen |60 for checking or Calibrating the equipment.

Scrambling circuit Rate and drift pulses retransmitted froml th rate and drift ground stations due to triggering by other similarly equipped aircraft may be seenv on the cathode ray indicator tube |62 (Fig. 1b), and for that reason a Scrambler circuit is provided as indicated by the block 221 in Fig. 1a for identifying the retransmittedrate and drift pulses due to triggering by the aircraft carrying the equipment of Figs. 1a and 1b.

A positive voltage pulseis applied periodically tothe Scrambler circuit 221 through a switch 228, and in response to each applied Vpositive pulse a negative voltage pulse of the proper timing and duration is applied Ifrom the Scrambler circuit 221 to a grid of a frequency divider tubel (not shown) inthe frequency divider ll. The Scrambler circuit represented by the block 221 may be any suitable wave shaping means such as a differentiating and clipping circuit for producing negative pulses of the proper timing and width. The negative pulse from the circuit 221 blocks the frequency divider tube momentarily and thus makes the divider inoperative for a period during and immediately following said negative pulse.

Thus, the operation of the frequency divider stages and l2 is stopped periodically so that when normal operation of the dividers is resumed the dividers will start with a phase relationship that is random with respect to their previous output. As a result, the pulses due to triggering by other aircraft will not be stationary on the cathode ray trace but, instead, they will appear to be jumping around the cathode ray trace when either the 100 mile or 10 mile scale is being used.

On the l mile scale, the effect of scrambling is different because the start of the timing sweep remains unchanged as it is produced directly from the 93 kc. oscillator. However, the particular half cycle of the 93 kc. wave that is selected by the puise selector is random. Consequently, it is not often that an interfering pulse will coincide with a sweep period that is unblanked.

The switches 228, 40 and 36 (Fig. 1a) and the switch 2|1 (Fig. 1b) are operated in a fixed time relation by means of cams (not shown) which are driven by a common shaft as indicated by the broken lines 229 associated with the switches.

Fig. shows the sequence of operation for rate and drift pulse transmission and for scrambling It will be seen that at the end of each pulse transmission period, the scrambling switch 228 is closed momentarily to make the frequency dividers and I2 inoperative for a period equal to about one-half the pulse transmission period. The complete switching cycle may take about 16 second, this making the duration of each scrambling period about V60 second.

The circle-lighting amplier 208 (Fig. 1b) has +B voltage removed from its amplifier tubes for `a period substantially longer than the negative pulse from the Scrambler 221, specifically, for a period equal to the scrambling period so that no pips will appear on the indicator tube screen |60 during the occurrence of the negative scrambling pulse or during the short period immediately thereafter which is required for the frequency dividers and I2 to resume normal operation. The short period referred to above falls within the to second scrambling period. The +B voltage is removed from amplifier 208 periodically by means of a cam operated switch 23| which is driven synchronously with the other switches operated from the shaft indicated at 229. Preferably, the duration of' the negative scrambling pulse is adjustable so that the scrambling may be changed by the operator if some interfering pulses begin to appear stationary on the cathode ray trace.

Combination with, computer When the equipment described in the foregoing pages i's employed for bombing a target, it preferably is used in combination with a computer. The portion of the computer that is of interest in the present case is shown diagrammatically in Fig. 11.

The computer includes a constant speed motor 236 which drives the rate-pulse phase shifters 'through a variable speed drive 231 and a clutch 238. The clutch 238 is disengaged if the com- 1'2 puter is not to be used with the position determining equipment.

The variable speed drive 231 is of conventional design comprising a driving disc 239, a ball carriage 24| and a cylinder 242. The speed at which the rate-pulse phase shifters are driven is adjustable by means of a rack and pinion 243--244. The pinion may be rotated by a speed adjustment crank 246 so that the operator may adjust the rate of rotation of the pulse-rate phaseshifter rotors to a rate that holds the rate-pulse pip and the marker pulse pip coincident, as shown in Fig. 3, during a. bombing run. Thus, with these pips held coincident, the rate information is fed into the computer. The rate information is taken off the shaft of the cylinder 242 by bevel gears 241 to drive the input shaft of a differential unit .248 which may be of conventional design such as that shown in Fig. 12, for example.

The output shaft of the differential unit 248 drives the input shaft of a second differential unit 249, the output shaft of which drives the input shaft of a third differential unit 264. The out put shaft of unit 264 drives a train of gears 25|, 252 and 253, each pair of gears having a 10 to 1 ratio. The final gear of the train of gears carries a contact point 254 that makes contact with a contact member 256 after the final gear has been rotated a, predetermined amount, and the bombs are released automatically in response thereto.

The differential unit 249 is provided so that the distance from rate station to target may be preset into the computer before the aircraft takes off on the bombing mission. 'I'his is done by turning a crank 251 to run the contact point 254 back from its point of contact with member 256. A mileage counter 258 driven by bevel gears 259 shows in units, tenths and hundredths the mileage that has been set into the computer. The differential unit 264 is provided so that the distance known as trail" distance may be cranked into the computer at the crank 262, this distance appearing on the counter 263.

The differential unit 248 is provided for the purpose of cranking range into the computer. The position of the bomb release contact point 254 is changed by way of the differential 248 whenever an adjustment is made in the speed of rotation of the rate-pulse phase Shifters for maintaining pulse coincidence. This automatic adjustment is accomplished by coupling the adjustment shaft of the differential unit 246 through a multiplier unit 26| to the speed adjustment crank 246. Since range is a product of rate" and "time of fall, the time of fall is cranked into the computer from a crank 266 through a rack and pinion 26T-268 and through the multiplier 26| to the adjustment shaft of the differential 248. The "time of fall that is cranked in is shown in seconds on a counter 259.

It will be apparent that time of fall" of the bomb (which is a function of altitude) and the rate (which is the speed at which the aircraft is moving away from or toward the rate ground station) are multiplied in the unit 26| to obtain range. It will also be apparent that while the rate station pip and the marker pip are being held coincident, the correct value of rate is being set automatically into the multiplier 26|.

'I'he multiplier unit 26| may be of any suitable type. In the example illustrated, it is designed the same as the variable speed drive 231.

Operation with computer First it should be noted that when'the rate pulse pip and the marker pip are aligned, the reading of the counter 81 is the distance of the bomber from the rate ground station, the bomber referred to being the one carrying the equipment being described. Actually, the counter 81-and the counter 258 read a maximum of miles which is more than the maximum length of a bombing run. Therefore, if the counter 81 is used to determine the full distance from the rate station, the number of times it counts 10 miles must be noted as the bomber is own toward the target. In practice, the bomber is navigated by any suitable method to the point where the bomb The reading of the target distance counter 258 the distance from the rate station to the target, tins distance being set in before the bomber takes o on the bombing mission.

ffThe presetting of the computer prior to take oli for a bombing mission is done as follows:

(I) The bomb release contact point i254 is brought into contact with the contact point 256, i. e., it is set to the bomb release position.

(II) Next the contact point 254 is run back by turning the crank 251 until the target distance counter 258 reads distance from rate station to target. The number of times the counter passes through the maximum reading of ten miles must be noted as the crank 251 is operated. It will be understood that now if the crank 13 or the contact speed motor 236 is operated so as to align the rate station pip and the marker pip, the target distance counter 258 will then read distance from the bomber itself to the target.

(III) 'I'he distance known as "trail is set in by means of the crank 262, the trail distance counter 263 and a differential unit 264. Trail ls due to the air resistance presented to the bomb after its release and is the distance that the bomber would be past the target when the bomb hit the target if the bomber continued its course. The trail distance may be preset because the bombing is to be done while maintaining a predetermined air speed and altitude. Preferably, a windage correction is included in the trail setting.

(IV) "Time of fall is set in by the crank 265 through the multiplier 26|. This may be preset into the computer because the bomber is to bomb from a predetermined altitude. The output of the multiplier gives the range which is the product of time of fall and .ratej the latter being fed into the multiplier fduilingvlthe bombing run while the rate plsep" (ndfmarker pip are being held coincidentigg, y '1 f' Note is made of the fac t `the rate fed into the multiplier 26| depends-upon the angle o the bombing run with respect to the line from rate station to target. Thus there is an automatic correction for this angle and no special setting or adjustment for it is required.

(V) 'I'he drift station phase Shifters are set by means of the crank 13 and the knob 89 so that the drift station pip and the marker pip will be coincident at a predetermined bomb run distance from the drift ground station. This distance appears on the counter 81.

The bombing run It will be understood that the course for av marker pip. He also holds the altitude and air speed at the predetermined values.

The bombardier, by adjusting the crank 246, holds the rate station pip coincident with the marker pip. At the proper time the bomb release contact points close and the bombs are automatically released.

I claim as my invention:

l. I n a position determining system foi` a craft wherein there is a radio repeater ground station for receiving and re-transmitting periodically recurring radio pulses, craft borne equipment that'comprises a radio transmitter for transmitting said radio pulses to said ground station, means Lfor receiving said radio pulses after retransmission from said ground-station, means for producing periodic timing pulses, said craft borne equipment further comprising a cathode ray iiidicator tube having a viewing screen, means for deiiecting the cathode ray along a time axis periodically to producea trace onr said screen said deflections having a definite time relation, with respect to the timing pulses, means for causing said periodic timing pulses to produce an index mark on said trace, means for causing said retransmitted pulses to produce indications on said trace, a continuously rotatable phase shifter unit for shifting the time of transmission of said radio pulsesfrom said craft with respect to said timing pulses, said phase shifter unit comprising a plurality of goniometers having their rotors eff 3. Thefinvention according to claim 1 wherein,

means is' provided for indicating as a function of the setting of the phase shifter unit the instant that a predetermined position of h i c been reached. t e mart han 4. In a position determining system for a craftl wherein there are two ground radio repeater stations rfor receiving and retransmitting,periodically recurring rate pul=esl and drift pulses re s ec craft borne .equipment p twel'y ground stations, :specradio means for receiving said 4rate Iand drift pulses after retransmission.,l fromsaid ground stations, means for producing periodic timing pulses, said craft borne equipment funther comprising a cathode ray indicator tube having a viewing screen, means for deflecting the cathode ray along a time axis periodically'to produce a trace on said screen, said deflectionshaving a definite time relation with respect to the timing pulses, means for causing said periodic timing pulses to produce an index mark on said trace, means for causing said received rate and vdrifv4 pulses to produce indications on said trace, la continuously rotatable phase shifter unit for shifting the time of transmission of said rate pulses from said craft with respect to said timing pulses, said phase shifter unit comprising a plurality of goniometers having their rotors effectively coupled to each other so that they rotate at different speeds, and means for continuously rotating the rate-pulse phase shifter unit whereby the indication produced by the retransmitted rate pulses may be caused to remain coincident with said index mark as the craft moves away from or toward the rate-pulse ground station.

5. In a position determining system for a craft, radio equipment on said craft for transmitting radio pulses to a ground station and for receiving said pulses after retransmission by said ground station, additional equipment on said craft which comprises a master oscillator having an output signal of constant frequency, a chain of frequency dividers connected to said oscillator for supplying signals that have frequencies which are submultiple frequencies of the oscillator frequency, a cathode ray indicator tube having a viewing screen, means for deflecting the cathode ray of said tube along a time axis in synchronism with a selected one of said submultiple frequency signals to produce a trace on said screen, means for producing submultiple pulses from said multiple frequency signals, respectively, pulse selector means, means for supplying to said selector means said oscillator output signal and said submultiple frequency pulses for selecting fractional cycle pulses from said oscillator output signal which recur at the lowest submultiple frequency, means for causing said selected pulses to produce index mark indications on said cathode ray trace, means for causing the pulses received from said ground station to produce indications on said trace, a continuously rotatable phase shifter unit for shifting the time of transmission of said radio pulses from said craft with respect to said timing pulses, said phase shifter unit comprising a plurality of goniometers to which said oscillator output and said submultiple frequency signals are applied, respectively, said goniometers having their rotors geared to each other with the gear ratio between successive rotors proportional to the frequencies of the signals applied to the goniometers, respectively, means for continuously rotating the phase shifter unit whereby the indication produced by the retransmitted radio pulses may be caused to remain coincident with said index mark as the craft moves away from or toward said ground station.

6. In a position determining system for a craft, radio equipment on said craft for transmitting radio pulses to a ground station and for receiving said pulses after retransmission by said ground station, additional equipment on said craft which comprises a master oscillator for supplying an output signal, a chain of frequency dividers connected to said oscillator for supplying signals that have frequencies which are submultiple frequencies of the oscillator frequency, a cathode ray indicator tube having., a viewing screen, means for deiiecting the cathode ray of said tube along a time axis in synchronism with a selected one of said submultiple frequency signals to produce a trace on said screen, means for producing timing pulses, means for causing said timing pulses to produce index mark indications on said cathode ray trace, means for causing the pulses received from said ground station to produce indications on said trace, a continuously rotatable phase shifter unit for shifting the time of transmission of said radio pulses from said craft with respect to said timing pulses. said phase shifter unit comprising a` plurality of goniometers to which said oscillator output signal and said submultiple frequency signals are applied, said goniometers having their rotors geared to each other with the gear ratio between successive rotors proportional to the frequencies of the signals applied to the goniometers, means for producing submultiple pulses from said submultiple frequency signals, respectively, after they have passed through said goniometers, pulse selector means, means for supplying to said selector means said oscillator output signal and said submultiple frequency pulses for selecting fractional cycle pulses from said oscillator output signal for utilization as modulating pulses for producing the radio pulses transmitted from the craft, and means whereby the phase shifter unit may be continuously rotated for keeping the indication produced by the retransmitted rate pulses coincident with said index mark as the craft moves away from or toward the ground station.

7. In a position determining system for a craft, radio equipment on said craft for transmitting radio pulses to a ground station and for receiving said pulses after retransmission by said ground station, additional equipment on said craft which comprises a master oscillator having an output signal of constant frequency, a chain of frequency dividers connected to said oscillator for supplying signals that have frequencies which are submultiple frequencies of the oscillator frequency, a cathode ray indicator tube having a viewing screen, means for deflecting the cathode ray of said tube along a time axis in synchronism with a selected one of said submultiple frequency signals to produce a trace on said screen, means for producing submultiple frequency pulses for utilization as timing pulses, means for causing said timing pulses to produce index mark indications on said cathode ray trace, means for causing the retransmitted pulses received from said ground station to produce indications on said trace, means including a continuously rotatable phase shifter unit for shifting the time of transmission of said radio pulses from said craft with respect to said timing pulses, said phase shifter unit comprising a plurality of goniometers to which said oscillator output signal and said submultiple frequency signals are applied, respectively, said goniometers having their rotors geared to each other with the gear ratio between successive rotors proportional to the frequencies of the signals applied to the goniometers, re-

` spectively, a modulating-pulse selector means,

means for producing submultiple pulses from the submultiple frequency signals after they have passed through said goniometers, respectively, means for supplying to said modulating-pulse selector means said last-mentioned submultiple frequency pulses and also said oscillator output signal after it has passed through one of said goniometers whereby fractional cycle pulses from said oscillator. output signal are selected for utilization as said modulating pulses the timing of which depends upon the adjustment of said phase shifter unit, said modulating pulses being supplied to the craft borne radio transmitter` for transmission to the ground station as said radio pulses, and means whereby the phase shifter unit may be continuously rotated for keeping the indication produced by the retransmitted radio pulses coincident with said index mark as the craft moves away from or toward said ground station. .a

8. In a position determining system for a craft, radio equipment on said craft for transmitting radio pulses to a ground station and for receiving said pulses after retransmission by said ground station, additional equipment on said craft which comprises a master oscillator having an output signal of constant frequency, a chain of frequency dividers connected to said oscillator for supplying signals that have frequencies which are submultiple 'frequencies of the oscillator frequency, a cathode ray indicator tube having a, viewing screen, means for deiiecting the cathode ray of said tubealong a time axis in synchronism with a selected one of said submultiple frequency signals to produce a trace on said screen, means for producing submultiple pulses from said multiple frequency signals, respectively, a timing-pulse selector means, means for supplying to said timing-pulse selector means said oscillator output signal and said submultiple frequency pulses for selecting fractional cycle pulses from, said oscillator output signal for utilization as timing pulses, means for causing said timingpulses to produce index mark indications on said cathode ray trace', means for causing the retransmitted pulses received from said ground station to produce indications on said trace, means including a continuously rotatable phase shifter unit for shifting the time of transmission of said radio pulses from said craft with respect to said timing pulses, said phase shifter unit comprising a plurality of goniometers to which said oscillator output signal and said submultiple frequency signals are applied, respectively, said goniometers having their rotors geared to each otherwith the gear ratio between successive rotors proportional to the frequencies of the signals applied to the goniometers, respectively, a, modulating-pulse selector means, means for producing additional submultiple pulses from the submultiple frequency signals after they have passed through said goniometers, respectively, means for supplying to said modulating-pulse selector means said additional submultiple frequency pulses and also said oscillator output signal after it has passed through one of said goniometers whereby fractional cycle pulses from said oscillator output signal are selected for utilization as said modulating pulses the timing of which depends upon the adjustment of said phase shifter unit, said modulating pulses being suppliedto the craft borne radio transmitter for transmission to the ground station as said radio pulses, and means whereby the phase shifter unit may be continuously rotated for keeping the indication produced by the retransmittedradio pulses coincident with said index mark asl the craft moves away from or toward said ground station.

9. The invention according to claim 8 wherein means is provided for interrupting the operation of said chain of frequency dividers at a periodic rate.

10. The invention according to claim 8 wherein periodic radio pulses are transmitted alternately to rate and drift ground stations and wherein the operation of said chain of frequency dividers is interrupted between the periods of said transmissions to said rate and drift groundvstations. y

11. In a position determining system Afor a craft wherein there are two ground radio repeater stations for receiving and retransmitting l 8 periodically recurring rate pulses and drift pulses,

respectively, craft borne equipment that com` prises a radiotransmitter for transmitting said rate pulses and said drift pulses to said ground stations. respectively, means for receiving said rate and drift pulses after retransmission from said ground stations, means for producingl pe.-

riodic timing pulses, said craft-borne equipment further comprising'a cathode ray indicator tube having a viewing screen, means for deilecting `the cathode ray along a time axis periodically said trace, continuously rotatable phase shifter units for shifting -the time of transmission of said rate vand drift pulses, respectively, from said craft with respect to said timing pulses,

motor driving means for continuously rotating the rate-pulsephase shifter unit, and means for adjusting the vrate at which said driving means rotates said rate-pulse phase shifter unit whereby the indication produced by the retransmitted rate pulses may' be caused to remain coincident with said index mark as the craft moves away from or toward the pulse-rate ground station.

12. Inv a position determining system for a craft wherein there are two ground radio repeater stations for receiving rate pulses and dri-ft pulses, respectively, craft-borne equipment that comprises a radio transmitter for transmitting said rate pulses and said drift pulses to said ground stations, means on said craft for receiving said rate and drift pulses after retransmission from said ground stations, said craft-borne equipment further comprising a cathode ray indicator tube and means .for producing a time sweep thereon, means for producing a periodic timing pulse vthat appears on said sweep as an index mark, means for causing said received rate and drift pulses to appear on said sweep, continuously rotatable phase shifter units for shifting the time of transmission from the craft of said rate and drift pulses, re pectively, a computer which includes a motor f iving'means, means for coupling said rate-puls phase shifter means to rsaid driving means forl continuously rotating said phase shifter, and means for adjusting the rate at which said driving means rotates said rate-pulse phase shifter unit whereby a received rate pulse indication may be caused to remain coincident with said index mark as the craft moves away from or toward the rate-.pulse ground station and whereby the rate of travel' of said craft away from or toward said ratepulse ground station is fed into said computer.

13.- In a position determining system for a craft wherein there are two ground radio repeater stations for receiving and retransmitting rate plses and drift pulses, respectively, craft-borne equipment that comprises a radio transmitter for` and drift pulses after retransmission from said ground stations, said' craft equipment further comprising a cathode ray indicator tube and means for producing a time sweep thereon,

means for producing periodic timing pulses that appear on said sweep to produce an index mark,v

means for causing said received -rate and drift pulses toappear on said sweep, continuously roground station and whereby the rate of travel 0f said craft away from or toward saidrate-pulse ground station is fed into said computensaid computer further including a bomb-release contact point and means for moving it towardits bomb-release position at a rate that is a function of the rate at which said rate pulse phase shifter unit is rotatedand means for changing the position of said contact point with respect to its bomb-release position in response to an adjustment of the rate at which said rate-pulse phase shifter unit is driven.

14. In a position determining system for a craft wherein radio equipment on said craft transmits radio pulses to a ground station and receives said pulses after retransmission by said ground station, additional enuipment on saidcraft v-hch comprises an oscillator for supplying an output signal, a chain of frequency dividers connected to said oscillator for supplying signals that have frequencies which are submulfiple frequencies of the oscillator frequency, a cathode ray indicator tube having a viewing screen, means for deflecting the cathode ray of said tube along a time axis in synchronism with a selected one of said signals to produce a trace on said screen, means for producing submultiple pulses from said submultiole frequency signals, respectively, pulse selector means, means for supplying to said selector means seid oscillator output signal and said subrnultiple frequency pulses for selecting fractional cycle pvlses from said oscillator output signal, said selected fractional cycle pulses recurring at the repetition rate of the lowest frequency submultiple freqrency pulses, means for causing said selected pulses to produce index mark indications on said caihode ray trace, and means for interrupting ataa periodic rate the operation of said frequency divider chain.

15. In receiving apparatus for indicating the timing of signal pulses with respect to timing pu1sessaid signal pulses being transmitted from a point remote from said receiving apparatus, a. cathode ray indicator tube having a viewing screen, means at said receiving apparatus for producing timing pulses recurring at a predetermined repetition rate, means for deecting thev cathode ray of said tube along a time axis at a pulse-repetition rate to produce a plurality of superimposed traces on said screen, means for f causing one of said signal pulses to produce a signal indication pip on one of said traces during one sweep of the cathode ray along the time axis,

and means for causing one of said timing pulses to produce an index indication` pip on another of said traces during a successive sweep of said cathode ray along the time axis and before the next signal pulse occurs whereby said two pips may be superimposed without adding to each other to produce a single pip instead of the desired two separate pips.

16. In receiving apparatus for indicating the timing of signal pulses with respect to jtiming pulses, said signal pulses being transmitted from a point remote from said receiving apparatus, a cathode ray indicator tube having a viewing screen, means at said receiving apparatus for producing timing pulses'recurring at a predetermined repetition rate, means for deflecting the cathode ray of said tube along a time axis at as repetition rate that is a multiple of said timing pulse repetition rate to produce a.k plurality of superimposed traces on said screen in the absence ing one sweep of the cathode ray along the time,V

axis, means for causing one of said timing pulses to produce an index indication pippnanother of said traces during a successive sweep of said cathode" ray along the time axis and before the next signal ypulse occurs whereby said two pips may be adjusted to the position of coincidence and still remain as two separate pips, and means for blanking all of the cathode ray sweeps except said two sweeps on which said signal and index pips appear. l

17. In a position determining system for a craft. radio equipment on said craft forl transmitting radio pulses to a ground station and for receiving said pulses after retransmission by said ground station, additional equipmenton said craft which comprises an oscillator for supplying an output signal, a chain of frequency dividers connected to said oscillator for supplying signals that have frequencies which are svbmultiple frequencies of the oscillator frequency, a cathode ray indicatortube having a Vviewing screen, means for deflecting the cathode ray of said tube along a time axis in synchronism with a selected one of said submultiple frequency signals to produce a trace on said screen, means for maintaining said indicator tube biased to cathode-ray cut-off in the absence of applied sgnals, means for producing timing pulses, means for causing said timingr pulses and the pulses received from said ground station to produce an index mark indication and a signal indication, respectively, on the traces produced by different successive deflections of the cathode ray, means for unblanking saidcathode ray during said diierent successive deflections only, and a continuously rotatable phase shifter unit for shifting the4 time of transmission of said radio pulses from said craft with respect to said timing pulses.

18. In a position determining system for a. craft, radio equipment on said craft for transmitting radici pulses to a ground station and for receiving said pulses after retransmission by said ground station, additional equipment on said craft which comprises an oscillator for supplying an output signal, a chain of frequency dividers connected to said oscillatorl for supplying signals that have frequencies which are submultiple frequencies of the oscillator frequency, a cathode ray indicator tube having a viewing screen, means for deilecting the cathode ray of said tube along a time axis in synchrnism with a selected one of said submultiple frequency signals to produce a .trace on said screen, means for maintaining said indicator tube biased to cathode-ray cut-off in the absence of applied signals, means for producing timing pulses, means for causing said timing pulses and the pulses received from said ground station to produce an index mark indication and a signal indication, respectively, on the traces produced by different successive deflections of the cathode ray, means for unblanking said cathode ray during said different successive deflectionsonly,

a continuously rotatable phase shifter unit for shifting the time of transmission of said radio successiverotors proportional to the frequencies' of the signals applied tothe goniometers, means for producing submultiple pulses from said submultiple frequency signals,I respectively, after they have passed through said goniometers,

pulse selector means, means for supplying to said selector means said oscillator output and said submultiple frequency pulses for selecting fractional cycle pulses from said oscillator output signal for utilization as modulating pulses for producing the radio pulses transmitted from the craft, and means whereby the phase shifter unit may be continuously rotated for keeping the indication produced by the retransmitted rate pulses coincident with said index mark as the craft moves away from or toward the ground station.

19. In a position determining system for a craft, radio equipment on said craft for transmitting radio pulses to a ground station and for receiving said pulses after retransmission by said ground station, additional equipment on said craft which comprises a master oscillator for supplying an output signal, a chain of frequency dividers connected to said oscillator for supplying signals that have frequencies which are submultiple frequencies of the oscillator frequency, a cathode ray indicator tube having a viewing screen, means for deflecting the cathode ray of said tube along a time axis in synchronism with a selected one of said submultiple frequency signals to produce a trace on said screen, means for producing submultiple pulses from said submultiple frequency signals, respectively, means for producing a delayed submultiple frequency pulse from the lowest submultiple frequency signal, a timing-pulse selector means, means for supplying to said timing-pulse selector means said oscillator output signal and said submultiple frequency pulses for selecting fractional cycle pulses from said oscillator output for utilization as timing pulses, said last means including means for selectively applying to the selector either the delayed or the undelayed lowest submultiple frequency pulse whereby a regular timing pulse or an offset timing pulse may be obtained, means for causing the selected timing pulse to produce an index mark indication on a cathode ray trace, means for causing the retransmitted pulses received from said ground station to produce an indication on said trace, and means including a continuously rotatable phase shifter unit for shifting the time of transmission of said radio pulses from said craft with respect to said timing pulses.

20. The invention according to claim 19 wherel in means is provided for biasing said indicator tube to cathode-ray cut-off in the absence of applied signals and wherein means is provided for utilizing said submultiple frequency pulses for unblanking the cathode ray during the reception of signal pulses and the occurrence of offset timing pulses only.

21. The invention according to claim 19 wherein means 1s provided for biasing sala' malestar tubeto cathode-ray cut-off `in the absence of applied signals and wherein means is provided for utilizing alternate higher frequency submultiple frequency pulses for unblankingl the cathode ray during the occurrence of received t:signlgl pulses and offset` timing pulses, respec- 22. The invention according to claim 19 wherein means is provided for biasing said indicator .tube to cathode-ray cut-offin the absence of applied signals and vwherein means is providedv for utilizing said delayed and said undelayed lowest frequency submultiple 'frequency pulses forunblanklng the cathode ray during the occurrence of received signal pulses 'and oflfset` timing pulses, respectively.

23. In a position determining system for a craft. radio equipment on said craft for transmitting radio pulses to a ground station and for receiving said pulses after retransmission'by said ground station, Vadditional equipment on said craft which comprises a master oscillator for supplying an output signal. a chain of frequency dividers connected to said oscillator for supplying signals that have frequencies which are submultiple frequencies of the oscillator frequency,v

a cathode .ray indicator tube having a viewing screen, means for deflecting the cathode ray of said tube along a time axis in synchronism with a selected one; of said submultiple frequency signals to produce a trace on said screen, means for maintaining said indicator tube biased to s cathode-ray cut-off ink the absence of applied signals, means for producing submultiple pulses from said submultiple frequency signals, respectively, means for producing a delayed submultiple frequency pulse from the lowest submultiple frequency signal, a timing-pulse selector means, means for supplying to said timing-pulse selector means said oscillator output signal and said submultiple frequency pulses for selecting fractional cycle pulses from said oscillator output for utilization as timing pulses, said last means including means for selectively applying tothe selector either the delayed or the undelayed lowest submultiple frequency pulse whereby a regular timing pulse or an offset timing pulse may be obtained, means for causing the selected timing pulse to produce an index'mark indication on a cathode ray trace, means for causing the retransmitted pulses received from said ground station to produce an indicationl on said trace, a circle-lighting pulse selector means, means for supplying the highest frequency submultiple frequency pulses to said last selector means, means for supplying both the delayed and the undelayed lowest frequency submultiple frequency pulse to said last selector means for selecting two of said highest frequency submultiple frequency pulses, means for utilizing said last two pulses for unblanking the cathode ray, and means including a continuously rotatable phase shifter unit for shifting the time of transmission of said radio pulses from said craft with respect to said timing pulses.

24. In a position determining system for a craft, radio equipment on said craft for transmitting radio pulses to a ground station and for receiving said pulses after retransmission by said ground station, additional equipment on said craft which comprises a master oscillator for supplying an output signal, a chain of frequency dividers connected to said oscillator for supplying signals that have frequencies which are sub- 23 multiple -frequencies oi' the oscillator frequency, a cathode ray indicator tube having a `viewing screen, means for deflecting the cathode ray of said tube along a time axis in synchronism with a selected one of said submultiple frequency signals to produce a trace on said screen, means for producing submultiple pulses from said submultiple frequency signals, respectively, means for producing a delayed submultiple frequency pulse from the lowest submultiple frequency signal, a timing-pulse selector means, means for supplying to said timing-pulse selector means said oscillator output signal and said submultiple frequency pulses for selecting fractional cycle pulses from said oscillator output for utilization as timing pulses, said last means including means for selectively applying to the selector either the delayed or the undelayed lowest submultiple frequency pulse whereby a regular timing pulse or an offset timing pulse may be obtained, means for causing the selected timing pulse to produce an index marklndication on a cathode ray trace, means for causing the retransmitted pulses received from said ground station to produce an indication on said trace, means including a, continuously rotatable phase shifter unit for shifting the time of transmission of said radio pulses from said craft with respect to said timing pulses,

said phase shifter unit comprising a plurality oi' means for producing additional submultiple pulses from themultiple frequency signals after they have passed through said goniometers, respectively, means forv supplying to said modulating-puise selector `means said additional sub,- multiple frequency pulses and said oscillator output signal after it has passed through one `of said goniometers for selecting fractional cycle pulses from said oscillator output for utilization as said modulating pulses, the timing of vsaid modulating pulses depending upon the adjust ment of said phase shifter unit, said modulating pulses being supplied to the craft borne radio transmitter for transmission to the ground station as said radio pulses, and means for continuously rotating the phase shifter unit whereby the indication produced by the retransmitted radio pulses may be caused to remain coincident with said index mark as the craft moves away from or toward said ground station.

STUART W. SEELEY.

REFERENCES `CITEDV The following references are of record in the le of this patent:

UNITED STATES PATENTS Hayes Oct. 14, 1947