Solid State Shortwave Receivers For Beginners - The Listeners Guide

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One final point is that with S.W. receiver designs it is not a good idea to deviate from the specified component values. These tend to be a little more critical than with other types of equipment and even if changing a component value does not prevent a receiver from working all together, it may well result in a loss of performance. 40
CHAPTER 3 General Purpose Receivers In this chapter a number of general purpose S.W. receiver designs will be described. These will all give good results on both the amateur and broadcast bands. Some of the circuits are extremely simple and inexpensive to construct, and others are a little more sophisticated. In general, and as one would expect, the more complex designs offer the best performance and greater flexibility in use, but even the more simple designs will provide excellent results. Regenerative FET Receiver (Fig.17) Field effect transistors (FETs) have several advantages over ordinary bipolar transistors in the stages of a S.W. that handle R.F. signals. There are two basic types of FET, Junction Gate FETs, and Metal Oxide Silicon FETs. These names are usually abbreviated to JUGFET and MOSFET respectively. Most MOSFETs currently in use have two gates, and are called Dual Gate MOSFETs. Any of these devices will work well in simple S.W. receiver designs, provided of course, that they are intended for use at high frequencies. In the present design a JUGFET is used, and this is the widely available and inexpensive 2N3819 device. The complete circuit diagram of the ‘Regenerative FET Receiver’ is shown in Fig.17, and as will be seen from this, apart from the FET, only one other active device is used. This is a 748C operational amplifier which is used here as a high gain audio amplifier. If we consider this circuit in greater detail, the aerial signal couples to the primary winding of T1, and the secondary winding of T1 together with VC2 forms the tuned circuit. VC2 is the normal tuning capacitor. The signals induced into the tuned circuit are coupled direct into the gate of Tr1. An FET has three terminals, and these are termed the gate, drain and source. These are the equivalents of the base, collector and emitter, respectively, of a bipolar transistor. The direct coupling to the gate of Tr1 will seem a little unusual to those who are unfamiliar with FETs. Unlike a bipolar device, a FET has quite a low resistance between its drain and source terminals with no bias applied to its gate. Whereas an ordinary transistor must be forward biased before it can be used as a practical amplifier, a FET must be reverse biased. This is achieved by using source resistor R2 and holding the gate at chassis potential. Usually a resistor is used to tie the gate to chassis, but in this case the tuned winding of T1 performs this task. 41
Page 1 and 2: Solid State Short Wave Receivers Fo
Page 3 and 4: SOLID STATE SHORT WAVE RECEIVERS FO
Page 5 and 6: CONTENTS Page CHAPTER 1 Frequency S
Page 7 and 8: CHAPTER 1 There is a strange fascin
Page 9 and 10: Propagation The reasons for the ama
Page 11 and 12: 41 Metres 7.1 to 7.3 MHZ 31 Metres
Page 13 and 14: e. A length of wire is connected to
Page 15: Crystal Set CHAPTER 2 Ultra Simple
Page 18 and 19: Components List for Fig.6 T1 Denco
Page 20: To those unfamiliar with this metho
Page 23 and 24: The completed chassis and panel are
Page 25 and 26: crystal set is not very high. This
Page 27: ted it would look something like th
Page 30 and 31: eceivers it does have too low a val
Page 32: to have on. connection earthed. In
Page 35 and 36: It is very worthwhile experimenting
Page 37 and 38: layer, acts as the dielectric of th
Page 39: level that reaches the detector of
Page 44 and 45: The output of Tr1 is developed acro
Page 47 and 48: Components List for Fig. 18 Resisto
Page 50 and 51: Components List for Fig.19 Resistor
Page 55 and 56: A.F. noise from Tr2 from reaching s
Page 57: The gain of the I.C. is fixed at ap
Page 60: Like MOSFETS, CMOS I.C.s can be dam
Page 63: CHAPTER 4 Portable Receivers One mi
Page 66: Normally the telescopic aerial shou
Page 72 and 73: A.M. Signal It will be helpful to f
Page 74 and 75: As should be apparent by now, if th
Page 78 and 79: the mains earth (regardless of whet
Page 80 and 81: Blank page 80
Page 82 and 83: Components List for Fig.30 R1 3.3k
Page 84 and 85: Components List for Fig.32 R1 3.3k
Page 86 and 87: Apart from increasing the sensitivi
Page 89 and 90: Components List for Fig.36 R1 390 o
Page 91 and 92:
prevent the oscillator from operati
Page 93:
BERNARDS No 222 Solid State Short W
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