f. The basic purpose of any receiver is to reproduce broadcast information in the audio range
(15Hz to 20KHz) as received from the transmitting station. The audio amplifier amplifies or magnifies
this information, after which the information may go through several stages or amplification to produce
a large enough signal to be processed by a power amplifier. After the information has been through the
power amplifier, it is then sent to the loudspeaker. The loudspeaker transforms the electrical signal
information back to sound waves where it is easily heard and understood.
g. The Automatic Gain Control operates the same in FM receivers as it does in AM receivers.
h. The Automatic Frequency Control can determine or sense deviation from a set frequency; its
job is to keep the receiver at the desired operations frequency.
2.
AM and FM receiver similarities and differences. There are both similarities and differences
between AM and FM receivers.
a. Comparing the input of both the AM and FM receivers shows they both have antennas, RF
amplifiers, mixers and a local oscillator. These blocks may be called "tuned," and will select one
broadcast station's composite-signal.
(1) The composite-signal consists of the carrier and the information. Amplify and mix the
composite-signal with the local oscillator signal and it will introduce an IF signal to the IF amplifier.
Here again, the composite-signal is amplified and sent to the detector.
(2) In the AM and the FM detector, the information is removed from the carrier, and sent to
the amplifier and converted to sound by the loud-speaker.
b. AM and FM differences.
(1) One difference between the two radio functions are the frequencies received and the
detection systems.
(2) Another difference is that the FM radio requires an AFC to stabilize the local oscillator,
thereby keeping the desired broadcast station tuned in.
NOTE:
Study and memorize the basic block diagrams of radios and of
televisions. Look for blocks that are common to all systems. Understand
the purpose and/or functions of the blocks. You will find by doing this
study and memorization, troubleshooting and servicing this unit will be a
lot easier.
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