6.9. CONSTRUCTION OF A SUPERHETRADIO

fig. 44

It is done by coupling two portions of a variable capacitor together. One of the portions is the part determining the frequency of the tuned circuit. The second portion is determining the oscillatorfrequency.

So both portions are changed strictly synchronically (they are turned by the same shaft) the frequency difference can be kept constant. This construction of a radio has several big advantages

1. The amplifiers amplifying the INTERMEDIATE FREQUENCY (called IF-amplifiers) can be tuned amplifiers which are tuned only to the very IF of this radio.

2. The energy of the desired radiosignal is increased very much, so that other stations fail the energy of “calling through” (being heard even though not desired).

SUMMING UP

We came to know now a series of different constructions of radios which have been invented step by step through the “history of radio technology”.

From step to step there was a technical improvement, always heading in direction to more sensitivity (being able to listen to distant stations) and more selectivity (being able to select only one station even if there are stronger stations near to the receiver) radios.

Fig. 45 to 47 should give you a general view about this development

fig. 45

fig. 46

fig. 47

CHECK YOURSELF:

1. What is the function of the different blocks of a radio!
2. Explain how a tuned frequency radio receiver is made up!
3. How is a superhetradio working?
4. What is the advantage of a superhetradio compared with a TRF radio?
5. What is the IF? Where and how is it produced?