|
|
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.
|
