PREREQUISITES FOR MAGNETIC RECORDING

To perform magnetic recording, you need three things:

• An input signal you wish to record.
• A recording medium. (This is a recording surface that will hold the signal you wish to record.)
• A magnetic head to convert the input signal into a magnetic field so it can be recorded.

If any one of these are missing, magnetic recording cannot take place.

Input Signal

An input signal can come from a microphone, a radio receiver, or any other source that's capable of producing a recordable signal. Some input signals can be recorded immediately, but some must be processed first. This processing is needed when an input signal is weak, or is out of the Frequency response range of the recorder.

Recording Medium

A recording medium is any material that has the ability to become magnetized, in varying amounts, in small sections along its entire length. Some examples of this are magnetic tape and magnetic disks. These are thoroughly discussed in chapter 2 of this module.

Magnetic Heads

Magnetic heads are the heart of the magnetic recording process. They are the transducers that convert the electrical variations of your input signal into the magnetic variations that are stored on a recording medium. Without them, magnetic recording isn't possible.

Magnetic heads actually do three different things. They transfer, or record, the signal information onto the recording medium. They recover, or reproduce, the signal information from the recording medium. And they remove, or erase, the signal information from the recording medium.

MAGNETIC HEAD CONSTRUCTION. - A magnetic head is a magnetic core wrapped with a coil of very thin wire (see figure 1-4). The core material is usually shaped like the letter C, and is made from either iron or ceramic-ferrite material. The number of turns of wire placed on the core depends on the purpose of that specific head. The gap in the core is called a head gap. It's here that magnetic recording actually takes place. We'll go into more detail of magnetic head construction in chapter 3.

Figure 1-4. - Magnetic field distribution around the head gap.

MAGNETIC HEAD OPERATION. - Whether you're recording on magnetic tapes or disks, all magnetic heads operate the same way. When an electric current passes through the coil of a magnetic head, magnetic field lines associated with the electric current follow paths through the core material. When the magnetic fields get to the head gap, some of them spread outside the core to form a fringing field. When a recording medium is passed through this fringing field, it is magnetized in relation to the electric current. This is called magnetic recording. Figure 1-4 illustrates this process.

Q.6 What three things are required to perform magnetic recording?
Q.7 What is the meaning of the term recording medium as it pertains to magnetic recording?
Q.8 What are the three functions of the magnetic heads on a magnetic recording device?