JPS5888809A - Recording and reproducing device for fm modulation signal - Google Patents

Abstract

PURPOSE:To increase the degree of pre-emphasis within a linear range of the input/output characteristics of a tape head system related to the exponent of modulation and to improve the S/N of a high band, by applying the pre-emphasis to the video signal. CONSTITUTION:The composite color video signal is converted into the signal S0 via a pre-emphasis circuit 7 and an FM modulating circuit 8. The circuit 7 has 10-14dB emphasis in terms of the ratio between a level near 10kHz and 3.58MHz for example. The FF10 and FF11 are triggered with the rise and the fall of the signal S0 respectively, and the output signals S1 and S2 are recorded on a tape via the output terminals 14 and 15 respectively. On the other hand, the reproduced FM modulation signal of each channel is synthesized through an exclusive OR gate 20. Then the signal S0 is extracted and then converted into the reproduced color composite signal via a demodulating signal 21, an LPF22 and a deemphasis circuit 23. Thus the reproduced signal S0 is set at 1/2<n> original exponent of modulation which is obtained before division.

Description

[Detailed description of the invention] 10. %FM modulated signal is divided into n (n=/-2, J...) signals each having its edge information. A recording and reproducing device for recording and reproducing FM modulated signals is used.

A modulation signal such as the one shown in Fig. 7, for example, F obtained by FM modulating a carrier signal with a frequency of f, using a video signal.
As shown in FIG. 1B, the M modulation signal 8 is composed of an FM modulation signal 81 whose level is inverted at each rising edge;
FM modulation signal 8 whose level is inverted at each falling edge
It is divided into 3 parts and recorded on magnetic tape. - As an example, as shown in Figure 1A, the circumference of the drum 1 is TIjJK/
gO @ Two rotating spatulas I'3A arranged at a spacing of /10'' on the magnetic tape 2 which is wound diagonally with a slightly larger winding angle.

By sliding contact of 3B alternately for each feel Y),
An FM modulated video signal is recorded. ■Transfer head 3
The configuration is such that one FM modulation signal is recorded as a separate I track by scanning A+1BtL/time. Tsuma 1
Three rotating heads have a track width of three,
Azimuth heads inclined in the same direction are located on both sides, and a spanner is located in the center.

FMgR1 for the heads on both sides/field
1 signal 81 t s= is respectively supplied, and track 4AI4B in the track pattern shown in #I diagram BK is formed. The other rotary head 3B has a similar configuration with a spade located in the center and λ heads located on both sides, and the direction of azimuth inclination is opposite to that of the rotary head 3A, so that it rotates once. As the head 3A continues scanning, a track indicated by 51.5B in Figure B is formed. Therefore, track 4 in FIG.
One FM modulation signal S is recorded as Al-51,
The other FM modulated signal 83 is recorded as track 4B, SB. Furthermore, the heights of heads ysA and 3B are shifted by l track for one rotation, n,)j? 5* and 5B are formed, and two new tracks are formed by the three K11 transfer students so that they do not overlap with the company and propositional tracks in the field of good law.

Nine FM modulated signals 81 and -1 reproduced from the magnetic tape 2
is threatened by Exclusideodate and is 5 yuan O
The signal is returned to the FM modulation signal 8 and then FM demodulated to obtain a reproduced video signal.

As mentioned above, the divided FM modulation method is used to record the FM that is played back.
The carrier frequency of the modulation signal can be reduced by %,
The transmission frequency band of the recording/reproducing device can be effectively utilized. For example, when FM modulating a conduit color video signal, FM modulation is performed such that the pedestal level is 9 MHz and the white level is 1 MHz, and the FM modulation signal 8 is as shown in Figure 3. ,9M
It has a frequency spectrum in which sidebands are distributed over frequencies corresponding to the color subcarrier frequency (<3-3 gMHz) for each of Hz and /JMHz. Since the frequency of the FM/modulated signal 818 divided into two is the same, the frequency spectrum thereof becomes as shown in FIG. 3B. As is clear from FIG. 3B, the L modulation index is reached when the frequency deviation between the pedestal level of the video signal and the white peak is half of JMHz/3MHz. In the case of FM modulation, as the modulation index becomes smaller, the second and higher sidebands become very small, and the ss/N ratio deteriorates.

The present invention aims to solve the problems of such a divided FM modulation system. There's more.

This invention calculates each modulation index of the divided signal.

Pre-emphasis is applied to the video signal so that the input/output characteristic of the modulation index via the tape head system is within a linear range and is approximately maximum.

Conventionally, when recording and reproducing FM modulated carrier signals using composite color video signals, the modulation index is limited to a range in which the level ratio of the carrier signal and the first sideband is linear with the modulation index. ,in particular,
The maximum modulation index of a color signal in a copper signal is about 0.7, and in that case, the amount of emphasis is ff (dB). In the 1-division FM modulation method, the FM modulation signal after division through the tape head system is
Focusing on the modulation index, the modulation index before one division is increased, and in the case of the above example, a larger Nori-emphasis than before is applied, such as (0,7X co=/, da). It is.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. Q shows the circuit configuration on the recording side, and FIG. S shows the circuit configuration on the reproducing side.

In FIG. 9, a four-digit digital video signal is supplied from a terminal indicated by 6, and is supplied to an FM modulation circuit 8 via a Norien 7 assist circuit 1.

FM modulation signal8. is formed. This pre-emphasis circuit 7 is, for example, 10 as shown by 9 in FIG.
Around KHz and 3-! ; g MHz to O ratio”r:/
It is said to have an emphasis characteristic of 0-/II (aB). In Fig. 6, the dashed line shows the I
This is the characteristic of the electronic fax circuit of n.

The FM modulation signal 8. emerging from the FM modulation circuit 8 is supplied to fritunoflora f10 and f11. One 7 lip 7
The 0 tube 1o is triggered by the rise of the FM modulation signal 8, and the FM modulation signal 81 appears at its output. the other 7
Ritsuzo Flotuso 11 is.

A trigger is triggered at the falling edge of the FM modulation signal S, and the output is the FM modulation signal S! appears. These FM modulated signals 81
The 1B proverbs are output to output terminals 14 and 15 via recording tubes 12 and 13, respectively.

As mentioned above, the data is recorded on the magnetic tape by a %-rotary head.

In addition, rotating head 3 A # 3 B from the magnetic tape
The FM modulation signal of each channel reproduced by K is the S-th
The signal is supplied from an input terminal indicated by 16.17 in the figure, and is synthesized by an exclusive video adder 20 via a reproduction amplifier 18.19, and an FM modulated signal 8. is taken out as its output. The signal is then demodulated by the FM demodulation circuit 21, unnecessary signals are removed by the low-pass filter 22, and is supplied to the de-emphasis 1 path 23. This de-emphasis circuit 23 has a de-emphasis characteristic complementary to the pre-en-7 assist characteristic 9 of the pre-en-7 assist path T provided on the recording side. At the output terminal 24, a reproduced color composite signal is obtained.

As can be understood from the above description of the embodiment, according to the present invention, F
Since the M modulation signal has the original modulation index before being divided, the amount of pre-emphasis is made larger than before within the range where the input/output characteristics of the P system with respect to the modulation index are linear. This makes it possible to improve the high-frequency S/N ratio compared to the conventional split FM modulation method. In principle, if /2B division is performed, the modulation index becomes F, so 2B times the emphasis can be applied.

Note that the present invention is applicable not only to recording and reproducing composite color video signals, but also to recording and reproducing a YC separation method in which luminance signals and color difference signals are separated. In the conventional YC separation method, the ratio between 10KHz and around 7.5MHz is /2-/g (dB)
However, when this invention is applied, an emphasis of 20-30 CdB is applied. In this way, even if the amount of emphasis is increased, overmodulation does not occur and the high-frequency S/N ratio can be improved.

[Brief explanation of drawings]

Figure 1 is a waveform diagram used to explain the divided FM modulation method, the figure 3 is a schematic diagram showing the structure of the head system and track pattern of a recording device to which this invention can be applied, and Figure 3 is a waveform diagram used to explain the divided FM modulation method.
Frequency spectrum used to explain M modulation method, @'f
FIG. 6 is a block diagram showing the configuration of the recording side in an embodiment of the present invention, FIG. S is a block diagram showing the configuration of the reproduction side of the embodiment of the invention, and FIG. FIG. 3 is a diagram showing frequency characteristics of an emphasis circuit. ! A I 3B...Rotating head, 7...Pre-emphasis circuit, 8...? M modulation circuit, 10.11-...
Fritzoflots! , 21...FM demodulation circuit, 23...
-De-emphasis circuit. Agent Masatomo Sugiura

Claims (1)

[Claims] FM made by FM modulating a carrier signal with a video signal
A modulated signal is divided into n pieces (nx
In an FM modulation signal recording and reproducing device that records and reproduces signals divided into signals of = /, ko, 3... The FM modulation signal O is characterized in that the video signal is configured to be pre-emphasized so that the input/output characteristic of the modulation index is within a range of lll5 and is substantially maximum. Feng regeneration device.