Method and circuit for the transmitting, recording, and/or reproducing of wide-band signals

A method and a circuit for transmitting or storing a wide-band signal in several, narrow-band channels, wherein frequency modulation and demodulation occur in the wideband channel. The uniformity of the transmission characteristics of the entire system is improved by obviating the necessity for multiple modulators and demodulators in the individual transmission channels.

The invention relates to a method for transmitting or storing wide-band 
signals in several narrow-band channels by sub-dividing the original 
signal into segments which are subjected to a first time transformation 
(expansion) prior to transmission or storage and subsequently to a second, 
reciprocal, time transformation (compression). 
BACKGROUND AND PRIOR ART 
A method for transmitting and recording signals covering a broad frequency 
band is known, for example, from German Pat. DE-PS 969 818 Ewerbeck. In 
the known method, the signal is split into several signals of narrow 
frequency width which are transmitted or recorded independently. In order 
to produce a plurality of signals equal in number to the number of 
available transmission channels, momentary values of the output signal are 
scanned with the aid of phase-shifted pulse trains. The chronologically 
correct recombination of the intermediate signals, which were transmitted 
or recorded in the individual channels, into the original signal, requires 
transmission of the scanning signal. 
The known method is not suitable for the transmission or recording of 
frequency-modulated signals in which the momentary values of the signal 
differ only in frequency but not in amplitude. Carrier frequency based 
transmission of the intermediate signals is basically conceivable and 
would also lead to a reduction of the required bandwidth of the individual 
transmission channels for the intermediate signals as compared to the 
bandwidth required for transmitting a frequency-modulated output signal. 
However, the equalization of the necessarily large number of modulators 
and the appearance of phase errors during recombination of the 
intermediate signals into the original signal cause extraordinary 
difficulties. In particular, where the intermediate signals are stored in 
several tracks of a magnetic tape, inaccuracies of the tape movement lead 
to intolerable phase errors among the individual channels and prevent 
satisfactory demodulation of the intermediate signals and gap-free 
recombination. 
Another system for decreasing the bandwidth requirement of a video 
recording and reproducing unit is known from the German published 
application DE-AS No. 22 37 255, to which U.S. Pat. No. 3,806,640, 
Furakawa, corresponds. As described there, a video signal containing 
arbitrary information is divided into a number of signals. These signals 
are recorded in several channels containing storage circuits. The video 
signal is shifted into a lower frequency range by performing the readout 
of the signal during a longer time interval than was used for recording. 
During reproduction, the recorded signals are again written into storage 
circuits and are then released in a shorter time interval than the 
write-in time interval. In this manner, the original time scale and the 
original video signal are restored. 
THE INVENTION 
It is a principal object of the present invention to provide a method for 
transmitting or storing wide-band signals in which the number of 
modulators and demodulators required for carrier-frequency transmission of 
the partial signals does not depend on the number of transmission 
channels, and in which, preferably, the tuning of the individual 
transmission channels is simple. Briefly, according to the invention, 
frequency modulation prior to sub-dividing the continuous signal into a 
plurality of signals distributed to individual channels. 
For use as television signals the signal segments subjected to time 
transformation advantageously correspond to one TV line length and the 
switching processes preferably occur in the gaps between signal-sensing 
intervals. 
A particular advantage of the invention is that transmission errors, 
especially amplitude errors of the transmission system, do not influence 
the level of the demodulated video signal, regardless of which of the 
transmission channels the signal is momentarily derived from. In this way, 
the component signals can be more readily re-combined to form the original 
signal with precisely correct timing and phase. 
In an advantageous feature of another embodiment of the invention, a color 
information signal is transposed into a frequency band which is largely 
free of FM sidebands, and is added in carrier-based form to the FM 
modulated composite television signal before signal division and time 
transformation. Analogously, the signal is retransformed and retransposed 
before being re-combined with the demodulated composite television signal. 
The elements needed for time transformation can thus be used for both 
signal components (luminance, chrominance) simultaneously. 
Advantageously, the separation takes place only after performing a time 
error compensation for both signal components.

DETAILED DESCRIPTION OF THE INVENTION 
The diagram of FIG. 1 represents an example of the current state of the 
art, according to which segments of television signals arriving at 
terminal 10 are subjected to a time transformation, e.g., time expansion 
in time stages Z. The time-transformed signal segments are simultaneously 
assigned to respective channels and are used to modulate in modulator 3 a 
carrier frequency, whereafter they are recorded by transducer 4.1, 4.2 . . 
. 4n of a tape. Because the modulation takes place after the segmentation 
and time transformation, the required number of modulators and of 
demodulators 5, as well of time retransformation stages 6 is equal to the 
number of channels or recording tracks used. A disadvantage of this system 
is the difficulty of obtaining exactly equal transmission characteristics 
for all channels and for the channel-related time transformations of the 
video signals. Success cannot always be achieved. 
In the method according to the invention which can be practiced with an 
exemplary system illustrated in FIG. 2, the video signal arriving at point 
10 is conducted to the input of a modulator 11, and is used to impress a 
modulation upon a carrier frequency in known manner. The 
frequency-modulated signal appearing at the output of the modulator 11 is 
distributed sequentially to n signal channels according to the position of 
the switches 12.1, 12.2, . . . 12.n. The switching sequencing control 
signal may be a timing signal present in the original signal, or a 
multiple or submultiple thereof. 
The signal segments in the individual channels for recording on individual 
tracks are expanded by a factor of "n" in the time expansion elements 
13.1, 13.2, . . . 13.n, resulting in a frequency transformation by the 
factor 1/n. The expanded and frequency-shifted signal segments are then 
recorded by means of transducer elements 14.1, 14.2, . . . 14.n onto 
adjacent tracks of a magnetic tape (not shown). For reproduction, the 
time-expanded signal segments stored on the magnetic tape are read out by 
means of the transducers 14.1, 14.2, . . . 14.n, and are transmitted to 
the time transformation elements 15.1, 15.2, . . . 15.n which perform a 
time compression. The signal segments present at the output of the time 
compression elements 15.1, 15.2, . . . 15.n once again correspond to the 
signal segments present at the output of the switches 12.1, 12.2, . . . 
12.n prior to expansion, and can thus be reassembled into a continuous, 
frequency-modulated signal by means of similar multiple switches 16.1, 
16.2, . . . 16.n. The reassembled signal passes through the demodulator 17 
and appears at its output as a demodulated, original video signal. 
The second embodiment of the invention, illustrated in FIG. 3, contains 
some of the same circuit elements shown in FIG. 2; they perform similar 
functions and carry the same reference numbers. In addition, the circuit 
according to FIG. 3 includes a filter and converter 18 for filtering the 
color information, or chrominance signal component out of the complete 
color video signal and shifting the carrier-based color selection, or 
chrominance signal component from, for example, 4.43 MHz to 0.562 MHz. 
This shifted color signal is superimposed onto the frequency-modulated 
composite television signal in the summing circuit 19. 
In a similar manner, the color component at 0.562 MHz is filtered out of 
the FM-modulated signal after the transmission, or storage, and is 
reconverted in the converter 20 to a frequency of 4.43 MHz, whereafter it 
is reassembled into the complete composite television signal in the 
summing circuit 21. 
The circuit according to the invention can thus carry out a method for 
storing frequency-modulated signals in several tracks or for transmitting 
them in several channels which makes it possible to equalize the 
transmission characteristics of the individual channels more easily than 
was heretofore possible. 
The method system and apparatus of the invention are capable of 
modifications and of combinations of individual features lying within the 
competence of a person skilled in the relevant art without departing from 
the scope thereof.