(3) The "local oscillator" produces an electronic signal of its own. This signal is sent to the
mixer block and is tunable. The main purpose of this block is to provide the electronic signal that is
generated in the radio receiver. The electronic signal will mix with the signal selected by tuning
elements in the RF amplifier. Newer models have a single knob that will allow for the tuning of the RF
amplifier and the local oscillator at the same time.
(4) The mixer receives signals from the amplifier and the local oscillator. These signals are
then mixed together electronically and as a result, there is a third signal produced. This third signal is
known as the IF, or Intermediate Frequency signal. The IF signal operates on a frequency 455Kh for the
AM radio. The IF amplifier block processes the signal that contains the same information as the
receiver from the broadcast station, along with a signal known as the carrier.
(5) The "IF" or "Intermediated Frequency" is the output frequency from the mixer. This
frequency is normally a fixed frequency where the superheterodyne receiver is concerned. Because the
IF amplifier can be tuned for excellent performance, it is easy to acquire high gain and optimum
selectivity.
2.
AM carrier transmission. So far the radio we've been discussing has processed a signal
containing two parts. One part consists of the intelligent information such as voice or music and the
other part is the carrier. As stated previously, the carrier carries the information from the transmitter to
the receiver at a certain frequency (each broadcast station operates at its own carrier frequency).
a. After the carrier transmits the information to the receiver, the carrier itself is processed along
with the information through the mixer. This operation produces another carrier at the IF frequency.
b. This new carrier has included in it the information that is sent out on the broadcast station's
carrier. Also, the intelligence contained in the IF carrier is sent through the IF amplifier to the
"detector."
c. The carrier, after this process, is not needed for any reason; therefore, the radio acts as
though this signal no longer exists. The detector's job at this point is to separate the carrier from the
information, thus sending the information portion to the audio amplifier.
d. The input of the "audio amplifier" is designed to accept a tiny electrical signal. The
electronical design of this block is able to amplify the electronic signal and apply enough power to
operate the loudspeaker.
e. The "power supply" of all electronic devices are designed to provide certain operating
voltages and currents from external sources, i.e., line voltage, battery, etc.
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