|Radio and Electronics (DED Philippinen, 66 p.)|
|5. MODULATION OF RADIOWAVES|
As we don't have to learn about the circuits for a radio transmitter within this course, we will only describe roughly how it works. For such a rough introductory description it is helpful to use a special kind of diagram. This diagram is called a BLOCKDIAGRAM, and it shows only rectangular blocks, which visualize circuits generally, by announcing their function only.
Fig. 31 shows the blockdiagram of a radio transmitter and fig 32 shows the signal how it will look like when it leaves the aerial.
This course will deal from now on, mainly with the following question:
HOW TO RECEIVE THIS SIGNAL IN A RADIO-RECEIVER?
HOW TO PROCESS THIS SIGNAL UNTIL IT CAN BE HEARD AT THE SPEAKER?
1. Explain how electromagnetic waves are produced!
2. Mention the parameters of electromagnetic waves!
3. Which different waves do you know and which are their special characteristics?
4. Which different bands of radiowaves do you know?
5. Which of these bands is useful for long distance communication?
6. Which of these bands is useful for short distance communication?
7. Give the frequency ranges of the different wavebands?
8. What does the term Fading meand, and what is its effect on reception?
9. Which band is used for communication from spaceships to earth and back?
10. What is the reason why long distance radio communication is not totally reliable?
11. What does the term modulation mean?
12. Which types of modulation do you know?
13. Calculate the % modulation for the shown case in fig. 30!