around this by amplifying this very weak Radio wave before it
reaches the detector by using Radio frequency amplifiers ahead
of the detector, then amplifying this again by the audio frequency
amplifier. R.F. amplification is also accomplished by
means of vacuum tubes. Modern receivers vary, in having from
1 to 4 stages of R.F. amplification.
From what we have just said, it is clear that a receiving
set can be thought of as having 4 main divisions--Tuning
apparatus, R.F. amplifiers, Detector, and A.F. amplifiers.
APPARATUS USED IN A RADIO RECEIVER
We have made considerable progress in the short time we
have spent in reading over this lesson. Let us go a step further
--and look at the actual apparatus used in receiving sets.
Fig. 15--Photo showing modern Radio receiver with apparatus shielded.
The one shown in the photograph (Fig. 14) employs seven
vacuum tubes, that serve various purposes, depending upon what
they are supposed to do. The first three vacuum tubes from the
left (center) of the picture are the radio frequency tubes used
to amplify the weak signals which come in from the aerial. The
next tube is the detector which takes the amplified radio signals
and changes them into audio signals so that they can be converted
into sound by using headphones or further amplified for
loudspeaker operation. The next two tubes are used to amplify
the audio signals so that they can satisfactorily operate a
loudspeaker.
We also see the coils of wire used for coupling one circuit
