the present invention will be now described in more detail with reference to accompanying drawings . fig4 shows an embodiment of the 90 ° phase - shift modulator according to the present invention . a main signal m 1 ( t ) applied through an input terminal i1 is provided to a first adder 2 through a buffer 1 , and is also provided to a pilot signal position controller 50 . next , the output of the pilot signal position controller 50 is multiplied by the output of a pilot signal generator 60 in a first multiplier 8 . an output of the first multiplier is applied through a pulse normalizer 3 to the first adder 2 and the output of the first adder is multiplied by an output of the pilot signal generator 60 in a second multiplier 5 . similary , an additional signal m 2 ( t ) applied through another input terminal i2 is provided to a third multiplier 15 through a time compensator 13 , thereby being multiplied by the image carrier wave applied through the 90 ° phase - shifter 29 from a reference signal generator . finally , an output of the second multiplier 5 is added to an output of a third multiplier 15 by the second adder 12 to generate the modulated signal xc ( t ). the pilot signal position controller 50 includes a horizontal synchronous - detector 9 with transistors and resistors , and a window generator 10 with a monostable multivibrator , and a position controller 11 with a monostable multivibrator . the pilot signal generator 60 includes an image carrier wave generator 4 with a crystal oscillator , a level converter 6 for converting ecl level to ttl level , and a divider 7 with counters . the first and second multiplier 5 and 15 , adders 2 and 12 are composed of the conventional gate circuits , while the time compensator 13 is composed of delay components . fig5 shows an embodiment of the 90 ° phase - shift demodulator according to the present invention . the modulated signal xr ( t ) received by the receiver is applied to both fourth and fifth multipliers 16 and 28 . low pass filters 17 , 30 and buffers 31 , 32 are connected to the output terminals of the multipliers 16 and 28 , respectively , to provide the demodulated main and additional signals . a pilot signal position detector 70 is connected between the low pass filter 17 and the buffer 31 , and outputs of an oscillating frequency generator 80 and the pilot signal detector 70 are applied to a phase detector 23 including mc4044 . the pilot signal position detector 70 includes a horizontal synchronous - detector 18 having transistors and resistors , a window generator 19 and a position controller 20 each having monostable multivibrator , and a pilot signal detector 21 and a waveform normalizer 22 having analog components . the oscillating frequency controller 80 includes a low pass filter 24 for filtering an output of the phase detector 23 , a voltage controlled oscillator 25 oscillating according to a dc level filtered by the low pass filter 24 , and a divider 26 for dividing the output of the voltage controlled oscillator 25 and applying the divided output to the phase detector 23 . also , an output of the voltage controlled oscillator 25 is applied to the fourth multiplier 16 after its level is converted to the same one as the modulated signal received by the receiver and at the same time an output of a level shifter 27 is applied to the fifth multiplier 28 through the second 90 ° phase - shifter 29 . fig6 shows a waveform diagram of a standard image level as a television signal adised by ccir and icc . fig7 is a waveform diagram representing the insertion of a pilot signal for a phase detection into an overscanning interval of a horizontal line of a standard image signal . fig8 shows an operation waveform diagram of fig4 where ( 8a ) represents a waveform of the main signal as the standard television signal , ( 8b ) represents a horizontal synchronous signal detected from the waveforms ( 8a ),( 8c ) represents the control signal for detection of only the pilot pulse which is made by shifting the position of the horizontal synchronous signal , i . e . the signal ( 8b ), as much as 7 . 8 μs and reducing its width to τ . subsequently , ( 8d ) is the output waveform of the divider 7 in fig4 which makes only one pulse transmitted during the time interval τ by dividing the output of carrier wave oscillator to be in the range of 680 khz to 2 mhz , and ( 8e ) is the output of the first multiplier 8 in fig4 which is extracted from the product of the control signal ( 8c ) by the waveform ( 8d ). ( 8f ) is a final modulated signal which is made by synthesizing ( 8e ) to ( 8a ) after shifting the level of ( 8e ). fig9 shows an operation waveform diagram of fig5 where ( 9a ) is a synchronous - detected waveform of signal ( 8f ) in fig8 through the transmission channel . ( 9b ) and ( 9c ) are the horizontal synchronous - detection and window generation signal and the position control signal , respectively , and ( 9d ) and is pilot signal which is detected from the product of signal ( 9a ) by ( 9c ). ( 9d ) is the same as signal ( 8e ). ( 9e ) is a normalized waveform by extending signal ( 9d ) used as a reference signal of the phase detector 23 in fig5 . ( 9f ) is the output waveform of the voltage controlled oscillator 25 in fig5 which is locked to ( 8d ) in fig8 . thus , ( 8d ) and ( 9f ) are waveforms with the same phase , being remotely locked by the pll . the present invention will now be explained by referring to fig4 to fig9 . the horizontal synchronous signal ( 8d ) is detected from the main signal m 1 ( t ) in fig4 i . e . the waveform ( 8a ) by the horizontal synchronous - detector 9 , and subsequently the output pulse ( 8c ) is generated by the window generator 10 and position controller 11 in fig4 . this signal acts as the control signal for the insertion of the pilot signal . similarly , the main signal m 1 ( t ) passing through the buffer 1 is added to the pilot signal provided through the pulse waveform normalizer by the first adder 2 to generate the waveform in the waveform ( 8f ). next , the added waveform ( 8f ) is applied to the second multiplier 5 and is subsequently applied to the second adder after it is modulated by the output of the image carrier wave generator 4 in the second multiplier 5 . the carrier wave of the image carrier wave generator 4 is converted to the proper level by the level converter 6 and the dividing number of the divider 7 which divides the frequency of the image carrier wave . this number should be correctly selected so that the output period of the divider is in the range of 0 . 5 μs to 1 . 5 μs and the output frequency of the divider becomes 1 / n ( n ; integer ) times that of the image carrier wave . the reason why the dividing number of the divider should be selected to satify such conditions is that only one pulse must be inserted during the pilot signal insertion interval of 2 μs and its frequency must be within the pass region of the low pass filter 17 shown in fig1 . the output of the position controller 11 , namely the pilot insertion interval pulse ( 8c ), is then multiplied by the output signal ( 8d ) of the divider 7 in the first multiplier 8 , thereby producing the pilot pulse waveform ( 8e ). this pilot pulse signal is converted to the proper level by the pulse waveform normalizer 3 to be synthesized with the main signal , and generate the final waveforms ( 8f ). similarly , the additional signal m 2 ( t ) is applied to the third multiplier 15 after it is compensated by as much as the signal process time of main signal m 1 ( t ) by the time - compensator 13 . after the time - compensated additional signal is modulated by the output of the first 90 ° phase - shifter 14 consisting of a differentiator circuit with resistor and capacitor ( not shown in figure ) of which the output phase differs as much as 90 ° from that of the image carrier generator 4 , the modulated additional signal is added to the modulated main signal by the second adder 12 . at this time , the phase angle θ of the phase - shifter 14 should satisfy the following formula . ## equ4 ## where , θ is of course 90 ° and the capacitance value should be selected in the range of 10 pf to 50 pf and the resistance value is automatically determined by the above formula . the modulated main signal m 1 ( t ) and additional signal m 2 ( t ) are orthogonal , that is , the phase difference is 90 ° so that they are multiplexed in the same signal frequency band without crosstalk of the two channels . the modulated output in fig4 is provided as the received signal xr ( t ) to the receiver through the transmission channel . the received signal xr ( t ) as shown in the signal ( 9a ) is multiplied by the output of the voltage controlled oscillator 25 of which frequency is the same as that of the image carrier wave in the transmitter in the fourth multiplier . the multiplied output , that is , demodulated signal is filtered by the low pass filter 17 so that the main signal m 1 &# 39 ; ( t ) is detected . similarly , the additional signal m 2 &# 39 ; ( t ) is demodulated by multiplying xr ( t ) by the output of the second 90 ° phase - shifter 29 and filtering the multiplied signal by the low pass filter 30 . next , the main and additional signals are provided through the buffers 31 and 32 , respectively . the level converter 27 is for increasing the amplitude of the carrier waves , i . e . cos ωt and sinwt by two times since the received level is reduced to half the transmitted level during the demodulation if it is not increased by two times . as mentioned before , the point of the present invention is to reduce the phase error θ . first , the horizontal synchronous - detector 18 detects the horizontal synchronous signal ( 9b ) from the main signal m 1 ( t ) filtered by the low pass filter 17 . next , the synchronous signal ( 9b ) is changed to the waveform ( 8c ) by the window generator 19 and position controller 20 , and the pilot signal ( 9d ) is detected by the pilot signal detector 21 . in order to drive correctly the pll , the duty cycle of the signal ( 9b ) is increased by the waveform normalizer 22 , thereby producing the signal ( 9e ) which is used as a reference signal of the phase detector 23 . after the output of the voltage controlled oscillator 25 is divided by the divider 26 , the divided output is applied to the phase detector 23 . then , the phase difference between the divided output of the voltage controlled oscillator 25 and the reference signal of the phase detector 23 corresponding to the output of the waveform normalizer 22 is detected . subsequently , the detected signal is applied to a varactor diode in the voltage controlled oscillator 25 after being smoothed a dc signal by the low pass filter 24 , so that the phase error becomes more and more reduced and at last it is locked to the same phase . ultimately , the phases of the image carrier waves in the transmitter and receiver are locked with each other by remote pll , hence the attenuation of the signal and crosstalk due to phase error and phase unbalance are removed . in summary , by inserting the pilot signal into the overscanned interval of the horizontal line of the standard image signal and using the pilot signal as the reference signal of the remote pll , the phases of the image carrier waves between the transmitter and receiver are locked to the same reference . the phase error due to the 90 ° phase - shift modulation and demodulation is removed and the signal attenuation and crosstalk are then removed at the same time . the present invention is described in the limited range of a main signal as applied to the composite image signal of an ntsc broadcasting system . an additional signal is applied as the information signal for high definition of an image signal in the television system for reproducing the image of high definition . in the case of teletext broadcasting or character multiplex broadcasting system , the image signal may be applied as the main signal and the text signal for the characters may be applied as the additional signal . the invention is in no way limited to the embodiment described hereinabove . various modifications of disclosed embodiment as well as other embodiments of the invention will become apparent to persons skilled in the art upon reference to the description of the invention . it is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention .