US 3792358 A
A single cycle transmitter at low and very low frequencies operates with an electrically short antenna. The transmitter produces an extremely short pulse of approximately one cycle duration. In response to a trigger signal, the transmitter's thyratron directly switches the antenna driving voltage, producing the first half cycle of a radiation pulse. The second half cycle is produced when diodes conduct. During this time, the thyratron deionizes, cutting off radiation.
Description (OCR text may contain errors)
United States Patent [191 Lewis et a1.
[ 1 SINGLE CYCLE TRANSMITTER  inventors: Edward A. Lewis, Harvard; John E. Rasmussen, Concord, both of Mass; James R. Stah1mann, Miramar, Fla.
 Assignee: The United States of America as represented by the Secretary of the Air Force, Washington, DC.
22 Filed: Dec. 15, 1972 21 Appl. No.: 315,745
 US. Cl 325/128, 325/162, 325/164, 325/169, 325/178, 325/186, 343/701  Int. Cl. H04b 1/04  Field of Search.... 315/346, 352, 356; 325/104, 325/105,125,l28, 120,121,141,161,162, 164, 166, 168, 169, 185, 186; 343/701 1 Feb. 12, 1974  Referenees Cited UNITED STATES PATENTS 3,659,203 4/1972 Rssn 325/105 Primary Examiner-Albert J. Mayer 57 ABSTRACT A single cycle transmitter at low and very low frequencies operates with an electrically short antenna. The transmitter produces an extremely short pulse of approximately one cycle duration. In response to a trigger signal, the transmitters thyratron directly switches the antenna driving voltage, producing the first half cycle of a'radiation pulse. The second half cycle is produced when diodes conduct. During this time, the thyratron deionizes', cutting off radiation.
2 Claims, 4 Drawing Figures ,5: H/Gf/ VdLT/ME Paws .surmy TIP/6G ER l/VP/JT' 5002c:
SINGLE CYCLE TRANSMITTER BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION A single cycle VLF, LF transmitter is provided which is designed to operate with an electrically short antenna. The transmitter includes a thyratron which in response to a trigger signal directly switches an extremely high DC antenna drive voltage to produce the first half cycle of a radiation pulse. The second half cycle is produced when a solid state high voltage diode conducts. During this time the thyratron deionizes, cut ting off the radiation.
DESCRIPTION OF THE DRAWINGS FIG. I shows in schematic form the basic embodiment for the single cycle transmitter;
FIG. 2 shows a typical waveform of the current from the antenna terminal of FIG. 1;
FIG. 3 shows the waveform of the transverse magnetic field at a distance of kilometers from the transmitter; and
FIG. 4 shows a second schematic circuit of the single cycle transmitter of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring in detail to FIG. 1, there is shown the basic embodiment of the VLF, LF single cycle transmitter for pulsing electrically short antenna 10. 48 KV DC high voltage power supply 11 having a negative output connects to ground and a positive output which charges transmitting antenna 10 through inductor l2 and diode 113. Antenna It) acts somewhat like an open ended section of a lossy transmission line, but the circuit may be understood by considering the antenna as a lumped capacitance C of about 6,000 pf (for an annal 10a. It is approximately one cycle of a sine wave, but the area under the second half cycle isslightly less than that of the first, so that for each actuation antenna 10 loses some charge. However, this is resupplied within 500 pisec by charge flowing through inductor 12 from high voltage power supply ll'l. Because of inductance 12, the voltage on the antenna 10 is about percent higher than the supply voltage. With antenna 10 charged to 60 KV, each actuation of the thyratron circuit consumes about 2 joules. For a 1.5 km antenna, the total radiated energy is estimated at 0.35 joule per actuation. When operated at 400 actuations per second the total radiated power is I40 watts, with a power consumption of 1,500 watts, resulting in an overall efficiency of about 10 percent for the basic transmitter. Of the total power consumed, 700 watts is used by the thyratron heaters. FIG. 3 shows the waveform of the trans verse magnetic field at a distance of IS km from the transmitter observed with a loop antenna resistively loaded to flatten the response.
FIG. 4 shows a second schematic circuit for a single cycle transmitter which is basically identical in structenna 1.5 Km long). Thyratron 15 is provided. It has control grid 15a, plate 15b, and cathode 150. When a trigger voltage from trigger input voltage source pulse generator 14 is applied to grid 15a of hydrogen thyratron 15, the charge flows from antenna 10 through inductance l9 (about 20 mh) for a time t 1r VLC 35 ,usec. The lumped capacitance C then has its maximum negative charge, thyratron 15 ceases to conduct, and charge flows back into antenna 10 through now conducting diode 18 for an additional 35 usec, at which time the lumped capacitance C is recharged positively. The system remains in this condition until thyratron 15 is triggered again. If the length of antenna 10 is reduced without charging inductance 19, the capacitance C is reduced and the transmitted pulse' is of shorter duration and smaller amplitude. FIG. 2 shows a typical waveform of the current from antenna termiture and operation to that illustrated in FIG. I. 50 KV high voltage supply 21 charges transmitting antenna 20 through charging inductor 22 and diode 23. Diode 23 consists of six high voltage diodes in series. Antenna 20 also has a fixed lumped capacitance C,. Antenna 20 is associated with tuning inductor 29. Tuning inductor 29 includes taps 29a 29d. Switch 31 selectively connects antenna 20 to the appropriate tape for antenna tuning purposes.
There is provided a pair of hydrogen thyratrons 2S and 25a operating inconjunction to handle more effectively the voltage required. Isolation transformers 26 and 26a provide the heater and :reservoir voltages to thyratrons 25 and 25a, respectively. Adjustable resistors 32 and 32a are utilized for control of the reservoir voltages of thyratrons 2S and 250, respectively. Resistors 33-38 conventionally utilized in association with thyratrons 25 and 25a to provide the proper operating voltages.Series arrangement of capacitor 39 and resistor 40 is in parallel arrangement with diode 28. A trigger voltage of 2,000 voltsof 2 user; duration is supplied from trigger source 24 to thyratrons 25 and 25a by way of isolation pulse transformers 27 and 27a, respectively. When the aforesaid'trigger is applied to thyratrons 25 and 25a, the charge flows from the antenna through the inductance for a time hereinbefore described. The lumped capacitance C of antenna 20 then has its maximum negative charge, the thyratrons cease to conduct, and charge flows back through diode 28 for an additional time substantially equivalent to the first named time, at which time lumped capacitance C, is recharged positively. The system remains in this condition until the thyratrons are triggered again.
What is claimed is:
I. A very high power single cycle transmitter at low and very low frequencies comprising electrically short antenna means for low and very low frequencies, said antenna means having a predetermined lumped capaci tance, first inductance means having a preselected magnitude, first diode means in a series arrangement with said first inductance means, a very high voltage power source having a positive and negativeoutput, with said negative output connected to ground, said positive output being connected to said antenna means by way of said series arrangement to charge said andiode means connected between said second inductance and ground becoming conductive upon the cessation of conduction in said thyratron means thus permitting a charge to flow back into said antenna means for a period substantially identicalto said preselected time, completing the second half of said single cycle at which time said lumped capacitance is recharged positively.
2. A very high power single cycle transmitter as described in claim 1 wherein said trigger means is comprised of a pulse generator.