US2466531A - Radio bomb release system - Google Patents

Description

D. BLITZ RADIO BOMB RELEASE SYSTEM April 5, 1949.V

Filed oct. 18. 1946 2 Sheets-Sheet 1 Q. n nfl va l N z mw L ku AN L? HTL w n L bk la A7 rom/Y I April 5, 1949. D. BLITZ 2,466,531

I RADIO BOMB RELEASE SYSTEM Filed oct. 18. 1946 2 sheets-sheet 2 v ATTUP/VY framed Apr. s, i949 .UNITED STATES. vmiTENT omer.

Daniel aslio Radio Corporation of America, a corporation of Wale ynem- Appueauon october 13,1946, serial 16.104.244

4 claims. (ci. 34a- 7) This invention lrelates to radio bomb release systems, and more particularly to improvements in systems of the type which-transmita signal from the bombing craft to a selected. target. receive the signal after reilection by the targ'et, and compare the transmitted and' received signals to determine the instant at which a bomb should be released to hit the target. One such system, using frequency modulated signals, is described in copending U. S. patent application Serial No. 524,794, filed March 2, 1944, by Royden C'. Sanders, Jr., and William R. Mercer, nowv Patent No. 2,412,632, issued December 17, 1946, and en-`v titled Radio bomb release system.

Owing to occasional transmission over multiple paths, caused by reflection from the sea or terrain lying between the bomber and its target, the signal received at the bombing craft will fade, disappearing and returning at intervals as the target is approached. When the signal disappears, the effect is similar to that of a remote target, and' the computer circuit tends to adjust itself accordingly. Upon reappearance of the signal, a certain amount of time is required for the computer to readjust to the true conditions. If this occurs just prior to the proper instant of release, no bomb will be dropped until the signal reappears, and the computer reaches its proper a minimum of additional circuits and components, avoiding any substantial increase in weight land complication of the equipment.

The invention will be described with reference to the accompanying drawing. wherein:

Figure 1 is a schematic diagram of a bomb release, system embodying the present invention,

Figure 2 is a graph showing the variations in frequency of the signals transmitted and received in the operation of the system of Figure 1,

Figure 3 isa graph showingthe variations in frequency, of 'a beat signal produced in the operation of 'thesystem of Figurel,

Figure 4 is ra graph showingv typical variation, as a targetis approached. of a control voltage produced in the operation of the system of Figure 1,7and

Figure 5 is a graph illustrating ideal variations of said control voltage at high and low speeds of the bomber craft, and a compromise between said extremes.

Refer to Figurel 1, which illustrates a system like that disclosed in the aforementioned copend ing Sanders application. A radio transmitter l. `provided with an antenna 3, is connected to a frequency modulator 5. The modulator 5 may be of the vibratory variable capacitor type described in patent application Serial No. 471,003, filed January 1, 1943, by Sydney V. Perry and entitled Capacity modulator unit. A square Wave generator 'l excites the modulator 5 through a wave I3. The transmitter l is also coupled to the detector i3 througha transmission line l5. The output vof the detector I3 is applied to an amplilier Il, and thence through an `amplitude limiter i9 to a differential counter circuit 2l. The counter circuit 2| is of the type described in said Sanders application Serial No.v 524,794, now Patent No. 2,412,632, issued December 17, 1946, comprising two averaging cycle counters provided with a common load resistor 23, arranged so that one provides a current flowing upward in the resistor 23 and the other provides a current flowing downward in the resistor 23. The counter 2| is electronicallyv switched by square wave voltage from the generator l, so that current flows down in the resistor 23 whenA the frequency of the transmitter i is increasing, and up when the vtransmitted frequency is decreasing.y

switch 28 is included between the relay 21 and the release mechanism. The relay circuit 21 is designed .to actuate the release when the voltage of its input decreases to a predetermined value. One such relay circuit, using a cathodeinput amplifier, is described in'the above-mentioned Sanders application.

In the system of said Sanders application, the counter output is applied directly to the relay circuit. The present system diifers therefrom in that a so-called memory circuit is provided between the counter and the relay. A capacitor 29 is connected across the input terminals of the relay 27. The upper terminal of the capacitor 29, together with the corresponding input terminal of the relay, is connected through a diode 3| to the counter load resistor 23. The diode 3l is arranged to allow conduction only from the capacitor 29 to the resistor23. A low pass lter comprising a resistor 33 and a capacitor 35 may be included between the resistor 23 and the diode 3l.

A resistor 31 is connected at one end to the upper terminal of the capacitor 29. The other end' of the resistor 31 goes to two switches, 33 and 4I. The switch 39, when closed, connects the resistor 30 to the tap on the voltage divider 25. 'I'he switch 3l, when closed, connects the resistor 39 to the positive end of the divider 25, which is at a potential in excess of that at which the relay 21 operates.

The switch 5I is ganged with the arming switch 28 so that when the switch 2B is open, the switch Ill is closed, and vice versa. The switch 39 is arranged to be held open normally by an electromagnet 43, and to close when the magnet 43 is deenergized. The coil of the magnet 43 is con nected to the output of a rectifier 45, which is supplied from the output of the amplier I'I.

The operation of the described system is as follows:

The transmitter I Aprovides a frequency modulated signal which is radiated by the antenna 3. Some of the radiated energy strikes the target and is reected back to the antenna I I and applied to the detector I3, where it is mixed with transmitter output reaching the detector through the line I5.

Referring to Figure 2.- the frequency of the transmitter output varies as shown by the solid line L The frequency of the signal received at the antenna I varies-as shown by the dash line 203. The variations in the received signal are delayed with respect to those of the transmitted signal by a time Td, which is the period required for radiation to travel from the antenna 3 to the target and back to the antenna I I, and hence is proportional to the distance, d. In addition (assuming the bomber is going towardthe target) the frequency of the received signal is shifted upward owing to doppler effect. This upward shift fs is proportional to the speed of approach s of the bomber to the target.

The output of the detector I3 includes a beat signal whose frequency fb is the difference in frequency of the transmitter output and the received signal. The beat frequency fb is lower during upsweep, or increase of transmitter frequency, than it is during downsweep, or decrease of transmitter frequency. Thedifference between the upper and lower values of fb is proportional to the speed s. The average value of fb is proportional to the distance d.

The beat output of the detector I3 is amplified by the amplifier I1, then limited toa constant amplitude by the limiter I9 and applied to the differential counter 2 I. The counter 2l provides; during upsweep. a current iu in the resistor 23, proportional to the lower value of the beat frequency jb. During downsweep, the counter 2l produces a current id in the opposite direction to the current i and proportional to the upper value of the beat frequency fb.

iu=kl (ad-bv) and id=ka(ad+bv) where a and b are constants determined in the design of the system, and k1 and k2 are the sensitivities of the counter circuit when operating positive and negative respectively. The average current in the resistor 23 (ilowing downward) is a= (k1-k2) ld-(k1+k2) bv and the resulting voltage drop (positive at the upper end of the resistor 23) is` The total potential at the upper end of the resistor 23, referred to ground, is

As the bomber approaches the target, Ec decreases because d is decreasing. The bias voltage E1 and the constants a. b, Ici and k2 are determined with respect to each other in advance, making due allowance for the altitude H at which the bombing run is to be made, so that Ec becomes equal to the voltage ED at which the relay is set to operate when was where g is the acceleration of gravity, 32.2 feet per second per second.

.The quantity is referred to hereinafter as the time from target, and is defined as the time which will be required under present conditions for the bomber to reach a point directly over the target. The quantity is the time of fall, i. e. the time required for a bomb released at an altitude H to reach the ground. If release is effected when the time from target equals the time of fall, the bomb will strike the target.

Owing to the fact that the radio equipment measures the slant speed and slant distance rather than the horizontal components of speed and distance, the equipment must be adjusted so that E1 follows an approximation rather than the true relation between speed and distance. This is described in detail in the above-mentioned Sanders application. It is suiiicient for the purpose of the present description to note that Ee decreases with decreasing time from target, and becomes equal toED when the time from target is equal to the time of fall.

Now suppose that as the bomber approaches the target, the received signal fades out. The control Voltage Ec, which has been decreasing in a substantially continuous manner (see Figure 4) immediately starts up to a maximum value corresponding to that which appears normally when the targetlE is remote. This results from-thermal c noise in the detector I I, which causes the counter age bearing a predetermined relationship to the time from target, relay means responsive to decrease of input voltage to a predetermined value to effect bombrelease, a storage device connected across the input terminals of said relay means,

means for initially charging said storage device d and o. However, the control voltage Ec does not return immediately to the proper value, because the filter capacitor 26 must be discharged down to Ec. As illustrated in Figure 4, this may not occur until after the time from target has decreased to less than the time of fall, and in the.

above-described Sanders system release will take place too late, or not at all, depending upon whether or not Ec gets down to ED before the bomber passes over the target and loses the signal entirely.

In `the operation of the instant system, the switches 28 and 4I are initially in the positions shown in Figure 1. As soon as a usable target signal is picked up, the coil t3 is energized to open the switch 39.` The capacitor 29 is then charged, through the switch 4| and the resistor 3l, to the full voltage appearing across the voltage divider 25. As the bombing run is started, the arming switch 28 is closed, opening the switch 4I; The capacitor 29 then discharges through I the diode 3|'A and the resistor 23 until the voltage across it is equal to the voltage Ec.

As Ec decreases in the manner shown in Figure 4, the capacitor 29 continues to discharge through the diode 3l to equalize its voltage with Ec. When the received signal fades, and Ecincreases, the diode 3l blocks, since it cannot conduct toward the capacitor 29. The switch 39 closes and the capacitor 29 continues to discharge through the resistor 31. The resistor 3l and the capacitor 29 are so proportioned that this discharge occurs at a rate approximating the normal decrease of Ec, which is indicated by the dash line 493 in Figure 4.

If the signal returnsl before the bomber reaches the release point, the magnet 43 reopens the switch 39 and the capacitor 29 starts to discharge through the diode as soon as Ec falls belowthe Voltage then existing across the capacitor 29. Thus if Ec returns to its correct value before the time from target becomes equal to the time of fall, the relay is controlled by current information, since the voltage applied thereto is kept equal to Ec. If Ec does not return to its proper value in time, release takes place anyway as soon as the capacitor 29 has discharged suiliciently through the resistor 31. y

Referring to Figure 5, the curve 50| represents the variation of Ec with time when the bomber is approaching the target at a relatively high speed, and the curve 503 shows how Ec varies when the bomber approaches at a relatively low speed. The resistor 3l and capacitor 29k are procraft, means transmitting a signal to a selected target and means for receiving said signal after reflection by said target to provide a control voltto a predetermined terminal voltage in excess of that which effects release, means normally discharging said storagedevice to a terminal voltage equal to said control voltage, a further discharge path, and means responsive to failure of said received signal to connect said further discharge path across said storage device to discharge said storage device at a rate approximating the normal rate of decrease of said control voltage.

2. A bomb release system including, on a mobile craft, means transmitting a signal to a selected target and means for receiving said signal after reflection by said target to provide a control voltage bearing a predetermined relationship to the time from target, relay means responsive to decrease of input voltage tc a predetermined value v to eiect bomb release, a capacitor connected across the input terminals of said relay means, means for initially charging said capacitor to a predetermined voltage in excess of that which eiects release, a discharge pathincluding a unilateral conductor connected to said capacitor and meansv to apply said control voltage to said discharge path to normally prevent discharge of said age, a resistor, and means responsive to failure of said received signal to connect said resistor across said capacitor to discharge said capacitor at a rate approximating the normal rate of de crease of said control voltage.

3. In a bomb release system including on a mobile craft means transmitting a signal to a selected target, means for receiving said signal after reflection by said target, computer means responsive to said transmitted and received signals to provide a control voltage bearing a predetermined relationship to the time from target, and relay means responsive to decrease of input voltage to a predetermined value to effect bomb release, a system for compensating the effects of fading or failure of said received signal including a capacitor connected across the input terminals of said relay means, means for initially charging said capacitor to a predetermined voltage in excess of that which effects release, a unilateral conductor connected between said computer means /and said capacitor to 'prevent conduction from resistor across' said capacitor to dischargel said capacitor at a rate approximating the normal rate of decrease of said control voltage.

4. In a bomb release system including on a mobile craft means transmitting a signal to a selected target, means for receiving said signal after reflection by said target, computer means responsive to said transmitted and received signals to provide a control voltage bearing a predetermined relationship to the time from target, and relay means responsive to decrease of input voltage to a predetermined value to eiect bomb release, a system for compensating the effects of fading or failure of said received signal including a capacitor connected across the input ter.- minals of said relay means, a direct current source of predetermined voltage in excess of that which emessi eiects release, an arming devicelncludmg means for initially connecting said capacitor to'l said source and, upon'arming,r to disconnectlt from said source, a unilateral rconductor connected between said computer means and said capacitor `to preventv conduction fromv said computer means received signal to connect said resistor 1: said capacitor to discharge said capacitor at a f rateapproximating the no1-mai rate of of said control voltage.

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'Emmons crrnn Y `The following references arey of record inthe n f f nient thispatent:y

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