GB2234622A

GB2234622A - An FM signal transfer-recording system for a VTR

Info

Publication number: GB2234622A
Application number: GB8915557A
Authority: GB
Inventors: Oh-Kwang Kwon; Jong-Kyung Yun
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1989-07-10
Filing date: 1989-07-07
Publication date: 1991-02-06
Anticipated expiration: 2009-07-07
Also published as: GB2234622B; DE3922681A1; DE3922681C2; GB8915557D0

Abstract

A VTR FM signal transfer-recording system having a video signal reproduction circuit (30) and a video signal recording circuit (40), the system comprising: an RF signal output from a low pass filter (6) of the reproduction circuit (30), which output is to be connected via a high frequency compensation unit (15) to the recording head (H2) of the recording circuit (40); a synchronisation-separating unit (14) which derives a synchronisation signal in the reproduction circuit (30); and a switching pulse generator (20) in the recording circuit (40) which applies the said synchronisation signal to synchronise operation of the recording circuit (40) with operation of the reproducing circuit (30). Recording directly the reproduced RF signal without FM demodulation and modulation and applying the synchronisation signal of the reproduction circuit (30) to the recording circuit (40) so as to synchronise the control pulses (21) and the drum servo (22) of the recording circuit (40) with the synchronisation signal of the reproduction circuit (30) enables image degradation during copying to be mitigated. <IMAGE>

Description

1 1 An FM signal transfer-recording system for a VTR The present invention

relates to an FM signal transfer-recording system for a VTR, particularly to a system which can reduce image degradation during copying, by directly recording the signal as read from the master tape on to the duplicate tape without involving the usual FM modulation and demodulation.

Generally, in a VTR, image signals recorded on the tape are read by a pick-up head and the amplified and FM modulated signals are used to generate brightness signals by FM demodulation. The low band (625KHz + 50OKHz) colour signals are demodulated and, subsequently, the brightness and colour signals are summed to form a complex image signal.

Similarly, for recordal, a complex image signal is received and the brightness and colour signals are separated therefrom. The separated signals are recorded on tape after FM modulation of the brightness signals and the low frequency modulation of the colour signals. Conventional tape-to-tape copying involves use of the normal reproduction and record functions and this results in image degradation.

Of course, because of the repeated FM modulation and demodulation, further image degradation occurs where a copy is made from a tape which is itself a copy.

I 2 With a view to mitigating the above mentioned disadvantage, the present invention has as its object the provision of an FM signal transfer- recording system in which a tape copy operation can be carried out by directly transmitting an RF signal from the reproduction circuit to the recording circuit with synchronisation of the switching pulse of the recording circuit with the synchronising signal of the reproduction circuit. Thus, the usual FM modulation and demodulation is avoided and image degradation upon copying is mitigated.

According to the present invention, there is provided a VTR FM signal transfer-recording system having a video signal reproduction circuit and a video signal recording circuit, the system comprising: an RF signal output from a low pass filter of the reproduction circuit, which output is to be connected via a high frequency compensation unit to the recording head of the recording circuit; a synchronisation-separating unit which derives a synchronisation signal in the reproduction circuit; and a switching pulse generator in the recording circuit which applies the said synchronisation signal to synchronise operation of the recording circuit with operation of the reproducing circuit.

An embodiment of the invention will now be described, by way of example only and with reference to the accompanying drawing, in which:- Fig.1 is a circuit diagram of an embodiment of the 3 present invention.

The illustrated circuit is formed of two major parts: a reproduction circuit 30 for reproducing image signals from a tape, and the recording circuit 40 for recording the output signal from the reproduction circuit 30. The reproduction circuit 30 and the recording circuit 40 can be implemented by two different VTRs or by a single, double-deck type, VTR.

The reproduction circuit 30 is similar to a conventional reproduction signal-processing circuit. Image signals are read by pick-up head H1 and amplified by a pre-amp 1. The signals are then applied to an AGC (automatic gain controller) 5, via a switch 4. If a drop-out occurs at any stage, a drop-out detecting unit 3 operates switch 4 as indicated in a figure. That is, an 1H delay unit 2 causes a signal delayed by 1H to be applied to the AGC 5.

The output of AGC 5 is applied to a low pass filter 6 and the output therefrom is subsequently applied to a low pass filter 7 of cut-off frequency 1.1 MHz. The output of filter 7 is applied to a colour reproduction unit 8 and from there to a mixer 13. The output of the low pass filter 6 is also applied to a limiter 9, whereby a signal of suitable level is obtained for demodulation. The signal from limiter 9 is applied to an FM demodulator 10, from there to a low pass filter 11, and next to a de-emphasiser 12. The output from de-emphasiser 12 is applied to a synchronisation-separating unit 14 and to mixer 13. The thus formed brightness signals and the colour signals are summed by the mixer 13, thereby reproducing the stored video signals. A separate synchronisation signal is derived by the synchronisation-separating unit 14.

The RF output signal (FM signal plus low band modulated colour signal) of the low pass filter 6 is also applied direct to a high frequency compensation unit 15 in the recording circuit 40. The signals from unit 15 are recorded on the duplicate tape by head H2, after passing through a pre-amp 16. The synchronisation signal from the synchronisationseparating unit 14 is applied, via a switch 17 to a vertical synchronisation-separating unit 18. Signals from unit 18 are applied to a momostable multivibrator 19 and from there to a 30Hz switching pulse generator 20. The 30Hz switching pulse is applied to a control pulse unit 21, a drum servo 22, and to pre-amp 16. In the case of normal VTR operation, the synchronisation signal 23 of the brightness signal system, in circuit 40, is selected using switch 17. When it its desired to copy a tape from circuit 30, the synchronisation signal from synchronisation signal separating unit 14 is instead selected using switch 17.

Operation of the circuits will now be explained.

First, the pre-amp 1 amplifies the FM modulated brightness signal and the low-band modulated colour signal as read from the tape by head H1. This RF signal (FM modulated signal plus low-band modulated signal) is normally applied to AGC 5 through switch 4. However, if drop-out occurs in the RF signal, the 1H delay unit 2 applies a 1H delayed RF signal to AGC 51 by operation of switch 4. The drop-out detector 3 transmits only the FM main carrier frequency component of the RF signal level. If the level is low, it is regarded as a drop-out, and the switch is connected as shown in figure 1. Thereby a 1H delayed signal is applied to the AGC 5 by the 1H delay part 2.

The low pass filter 6 is controlled to transmit only the neesssary component of the output of pre-amp 1. From low pass filter 6 the RF signal is applied to the low pass filter 7 which has a out-off frequency of 1.1MHz. Thus, only low-band modulated colour signals (629 KHz + 50OKHz) are transmitted the colour signal reproduction unit 8 and subsequently to mixer 13.

The output of low pass filter 6 is also applied to limiter 9 so that the signal is limited to a level suitable for FM demodualtion. The limited signal is applied to FM demodulator 10, the output of which is applied to a low pass filter 11. The output of filter 11 is applied to-deemphasiser 12 and the thus obtained brightness signal is applied to mixer 13 and to synchronisation-separating unit 14.

Thus, the brightness signal and the colour signal are -1 6 summed at the mixer 13 so that the recorded video signal is reproduced. Mixer 13 transmits the video signal to a video output for review, if desired.

moni Synchronisation-separating unit 14 separates the synchronisation signal out of the brightness signal.

The reproduction circuit 30 which performs these operations is similar to the conventional VTR. However, in the illustrated embodiment, an RF output signal from low pass filter 6 and a separated synchronisation signal from synchronisation-separating unit 14 are provided and are directly connected to the recording circuit 40. That is, the high fr- equency compensation unit 15 of recording unit 40 receives the RF signal transmitted from the low pass filter 6 and the synchronisation signal is applied to switch 17.

The RF signal is recorded on the duplicate tape by head H2, after passing through the pre-amp 16. The synchronisation signal is used to generate the 30Hz switching pulses by being passed via switch 17 to vertical synchronisation-separating unit 18, and then to momostable multivibrator 19 and finally being applied to switching pulse generator 20.

The 30 Hz switching pulses can be recorded on the control track.of the duplicate tape through the control unit 21. The pulses are also applied to the drum servo 22, thereby controlling the speed of the drum. Further, the pulses are also applied to the pre-amp 16, for channel 1 1 k 7 switching of the recorded signal.

Switch 17 is set so as to apply the synchronisation signal from synchronisation-separating unit 14 to the vertical synchronisationseparating unit 18 during the tape copy operation. In its alternative setting, switch 17 enables conventional operation of VTR circuit 40. In this setting, the synchronisation signal 23 of the brightness signal system of VTR 40 is applied to the vertical synchronisation-separating unit 18.

As mentioned above, the first part of the illustrated circuit reproduces the video signals to be copied, and the second part of the circuit rerecords the signals. The circuits can be implemented in separate Ms or in a single, double-deck VTR. The signals being reproduced in the reproduction circuit 30 can be simultaneously viewed on a monitor.

The reproduced RF signal is applied to the recording circuit 40 after drop-out compensation. A separated synchronisation signal is also applied to the recording circuit 40.

Thus, after the recording circuit 40 has compensated the RF signal applied from the reproduction circuit 30, using the high frequency compensation unit 15, and after the recording-pre-amplification by pre- amp 16, circuit 40 directly records the RF signal, using head 2.

The synchronisation signal derived by the synchronisation-separating unit 14 of the reproduction A 0 8 circuit 30 is processed to provide a vertical synchronisation signal by the vertical synchronisation separating unit 18 of circuit 40. The synchronisation signal is applied via monostable multivibrator 19 to switching pulse generator 20. The 30Hz switching pulse signals can be recorded on the control track of the duplicate tape. The signals are also applied to pre-amp 16, for channel switching of the recorded signal.

As mentioned above, the present invention can avoid image degradation, sometimes referred to as "blazing", which is caused by FM demodulation and modulation. This is achieved by directly recording the reproduced RF signal without FM demodulation and modulation, and by applying the synchronisation signal of the reproduction circuit to the recording circuit - so that the control pulse and the drum servo thereof can be synchronised with the synchronisation signal of the reproduction circuit.

The invention is not limited to the embodiment described herein above. Various modifications of disclosed embodiment as well as other embodiments of the invention will be readily apparent to persons skilled in the art upon reference to the above description of the invention. All such modifications and embodiments fall within the scope of the invention.

k 9

Claims

CLAIMS:

1. A VTR FM signal transfer-recording system having a video signal reproduction circuit and a video signal recording circuit, the system comprising: an RF signal output from a low pass filter of the reproduction circuit, which output is to be connected via a high frequency compensation unit to the recording head of the recording circuit; a synchronisation-separating unit which derives a synchronisation signal in the reproduction circuit; and a switching pulse generator in the recording circuit which applies the said synchronisation signal to synchronise operation of the recording circuit with operation of the reproducing circuit.

2. A signal transfer-recording system as claimed in claim 1, wherein the recording circuit comprises in addition to the head, high frequency compensating unit and the switching pulse generator, a two-position switch, a head pre-amp, a vertical synchronisation separating unit, a monostable multivibrator, a control pulse unit, a drum servo and a brightness signal system, the switch selectively connecting the said synchronisation signal or the brightness signal system to the vertical synchronisation separating unit which unit supplies signals to the multivibrator, the multivibrator suppling signals to the switching pulse generator and the output -110- thereof being applied to the pre-amp, the control pulse unit and the drum servo.

3. A signal transfer-recording system as claimed in claim 1 or 2, wherein in addition to the low pass filter, synchronisation-separating unit and RF signal output, the reproducing circuit comprises a drop-out detection unit, a second low pass filter, a colour reproducing part, a limiter, an FM demodulator, a third low pass filter, a de-emphasiser and a mixer, the output of the said low pass filter being applied to the second low pass filter and from there to the colour reproducing part so as to derive colour signals, the output of the said low pass filter also being applied to the limiter which is connected to the FM demodulator, which is in turn connected to the third low pass filter which is itself connected to the deemphasiser whereby brightness signals are derived, the brightness signals being applied to the synchronisation separating unit and the brightness signals and colour signals being summed by the mixer.

4. A signal transfer-recording system, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

Published 1991 at The Patent Office. State House. 66/71 High Holborn. LondonWClR4T?.FurLher copies maybe obtained froin Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Keys. Newport. NPI 7HZ- Printed by Multiplex techniques ltd. St Mary Cray. Kent 1