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Modulation aided recording on magnetic tape
                     
Patent application no. - 395/BOM/96
 
MAGNETIC TAPE RECORDER PLAYER TO RECORD AND RETRIEVE MULTIPLE MODULATED ELECTRICAL SIGNALS ON MAGNETIC TAPE.

This invention relates to recording of information on magnetic tape and retrieving the information recorded on magnetic tape.

Present method of recording information on magnetic tape is The information is converted into an electrical signal. The electrical signal is amplified and then fed to magnetic writing head that converts the electrical signal into magnetic field corresponding to the electrical signal that is generated by information to be recorded on the tape. These tiny magnetic fields are stored on a tape coated with magnetic material. Passing the magnetic tape over reading head retrieves the information. The tiny magnetic fields recorded on the tape create corresponding electrical signal in the coil of the reading head. This electrical signal is amplified and fed to output device  to reproduce the information that is recorded on the magnetic tape.  

Invention

The invention records more than one information signals on one magnetic tape. The information signals are converted into electrical signals and are used as modulating signals by modulating circuits to modulate carrier signals of higher frequencies. More than one carrier signals are modulated by information signals. Each information signal modulates one carrier signal. All modulated carrier signals are recorded simultaneously on a magnetic tape. The signal that is recorded on magnetic tape is resultant of mixture of all carrier signals, each modulated by one separate modulating signal (information signal).

Information is retrieved by reading the information on magnetic tape by magnetic reading head. The magnetic tape is passed over the reading head that creates electrical signals in the wire coil of magnetic reading head corresponding to information recorded on the tape. Signal red by this head is mixture of all carrier signals recorded on the tape, each carrier signal modulated by one separate modulating signal (the signal that is recorded on the tape). Adjustable tuning circuit selects one carrier signal. The tuning circuit selects only one carrier signal of specified frequency to which the tuning circuit is tuned and all other signals are suppressed (exactly like radio receiver that receives signal of specified frequency to which the receiver is tuned suppressing signals of other frequencies). The selected carrier signal is amplified and demodulated to obtain the modulating signal. The modulating signal obtained after demodulation is the actual information signal by which selected carrier signal was modulated at the time of recording the carrier signal on magnetic tape.

The frequency of the carrier signal that is selected can be changed since the tuning circuit is an adjustable tuning circuit (like user changes frequency of radio receiver).

The information recorded in modulated form on selected carrier signal is obtained after demodulating the selected carrier signal.

This recording and retrieving is done by one of the two types of modulation.
 



 


1.   Amplitude-modulation: Amplitude of carrier signal is changed in proportion to amplitude of the modulating signal.

2.   Frequency-modulation: Frequency of carrier signal is changed in proportion to amplitude of the modulating signal

Recording modulated electrical signal on magnetic tape. (Figure 1)

Figure 1 is a block diagram for recording multiple modulated electrical signals on a magnetic tape.

In Figure 1

S1, S2 and S3 are sources of information signals, like microphones; each source provides one information signal in electrical form that is to be recorded on magnetic tape.

Blocks 1, 4, and 7 are information signal amplifiers. Output of each amplifier is fed to separate electrical signal modulators.

Blocks 2, 5, and 8 are electrical signal modulators. Each signal modulator modulates the carrier signal fed to it by using information signal as a modulating signal. All modulators modulate carrier signals of different frequencies.

Blocks 3, 6, and 9 are carrier signal generators. Each carrier signal generator generates one carrier signal of specific frequency that is fixed for each generator and each carrier signal is fed to one modulator for modulating the carrier signal. The output signals of modulators are carrier signals, each of different frequency and each modulated by different information signal. At this stage there are more than one carrier signals each of different frequency and each modulated by different information signal.

The output signals of signal modulators are fed to block 10 that amplifies the signals. Output of block 10 is resultant signal of mixture of more all modulated carrier signals. Output of block 10 is recorded on magnetic tape by a magnetic tape writing head.

Retrieving modulated electrical signal recorded on magnetic tape.

Figure 2 is block diagram for retrieving modulated signal recorded on magnetic tape.

In figure 2

Block 1 is a reading device (playback head for reading magnetic tape)

Block 2 is an amplifier that amplifies electrical signal retrieved by the reading head. The retrieved electrical signal is resultant of mixture of all carrier signals that are recorded on the tape, each carrier is modulated by one information signal that was recorded on the magnetic tape.

Block 3 is an adjustable tuning circuit (Same circuit that is used in radio receiver to select one broadcasting station transmitted at specific frequency). The tuning circuit selects one carrier signal of specified frequency for which it is tuned by the user. All other signals are suppressed, except one signal of specified frequency to which the adjustable tuning circuit is tuned.

The selected carrier signal is amplified and demodulated in block 4. Block 4 is a demodulating circuit that demodulates the selected carrier signal to obtain the modulating signal. (Demodulating circuit is same circuit that is used in radio receiver to demodulate signal of the frequency selected by the user)

Output of block 4 is an original modulating signal that was used to modulate the selected carrier signal at the time of recording it on magnetic tape. The obtained signal is the information in the form of electrical signal.

Block 5 is a signal amplifier that amplifies output of block 4. Output of block 5 is the original information signal. This signal is fed to output devices for reproduction (block 6).

SALIENT FEATURES

In this recording, more information is stored on one magnetic tape. If four carrier signals are used to record information on one tape, one magnetic tape stores four times more information since each carrier signal carries one information signal.

To read information from the tape, selection of different carrier signals enables the user to retrieve information recorded over other carrier signal filtering out other signals. It is not necessary to load another tape  since one tape contains more  information.

Limitation

While erasing the information, all information recorded on the tape is erased since only one carrier signal cannot be erased from the tape.


 

 

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