Lesson 14:
Receivers
Objectives:
When the students have finished this lesson, they should be familiar
with the characteristics of receivers, including being able to identify
the different stages of various types of receivers, their functions, and
where they are located relative to each other.
Apparatus:
- HF receivers. One ideal prop for teaching this unit is a
communications receiver from the 1950's such a Hammarlund, National,
Racal or the like. Unlike modern integrated circuit receivers, these
receivers have discrete components for gain, tuning, bandwidth and so
forth that the student can see, and circuit test points that can be
monitored.
Explain that all of the same components are still in
modern receivers but that they may be integrated into a single chip or
simulated by a computer algorithm. The technology has not changed, only
the implementation.
- Frequency counter
It is suggested that you temporarily attach easily reached test
points to the receiver to avoid unfortunate accidents in class!
Handouts:
Receiver block diagrams.
Lesson Plan:
- Review any questions from the Chapter 13 homework.
- Using the receiver BFO show how the audio tone of a received
CW signal changes as the BFO frequency is varied, then show how
this affects the readability of an SSB signal. Use the
frequency counter to show that the BFO frequency is changing.
- Using the frequency counter, show the relationship between the
frequencies of the RF stage, IF stage, and the various oscillators that
control the frequency conversion. Do the calculations in detail
on the blackboard, even if these relationships seem trivial to
you.
- Change the bandwidth of the receiver using the CW and phone wide and
narrow filters. Make the point that you can't copy SSB through a
narrow CW filter and discuss why. If possible, extend this discussion to
an on-air demonstration of copying a narrow CW signal when the band will
not support a full SSB QSO.
- Discuss the differences, from a reception viewpoint, between AM
modes (CW, SSB and AM) and FM. Discuss why this leads to different
receiver requirements and point these differences out in the block
diagrams.
- When you are finished show a modern receiver as a
contrast; there are virtually no moving parts. This is the receiver on
a chip, a complete receiver on a single integrated circuit. There
are several available on the market.
- Demonstrate what one can determine from an S-meter. This is a good
place to review decibels.
- Emphasize that the exam requires that they know the relationship
between the various parts. The block diagrams are a help in mastering
this.
Homework:
- Read Chapter 14.
- Master the block diagrams.
- Do the Chapter 14 Quiz Questions.
- Skim Chapter 15.
Chapter 14 Quiz:
Printable copy of the Review
Quiz
Answers to Chapter 14 Quiz
1 |
D |
8 |
C |
15 |
B |
22 |
C |
29 |
D |
2 |
A |
9 |
B |
16 |
A |
23 |
D |
30 |
D |
3 |
C |
10 |
D |
17 |
A |
24 |
D |
31 |
C |
4 |
D |
11 |
C |
18 |
A |
25 |
D |
32 |
C |
5 |
C |
12 |
D |
19 |
B |
26 |
A |
* |
* |
6 |
A |
13 |
D |
20 |
B |
27 |
B |
* |
* |
7 |
C |
14 |
C |
21 |
A |
28 |
C |
* |
* |
Overhead Slide Versions of the Diagrams
- Slide 1
14.1
AM Audio Detector