AM/FM RADIO KIT MODEL AM/FM-108CK SUPERHET RADIO CONTAINS TWO SEPARATE AUDIO SYSTEMS: IC AND TRANSISTOR Assembly and Instruction Manual ELENCO ® Copyright © 2012 by ELENCO® All rights reserved. No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.
The AM/FM Radio project is divided into two parts, the AM Radio Section and the FM Radio Section. At this time, only identify the parts that you will need for the AM radio as listed below. DO NOT OPEN the bags listed for the FM radio. A separate parts list will be shown for the FM radio after you have completed the AM radio. PARTS LIST FOR THE AM RADIO SECTION If you are a student, and any parts are missing or damaged, please see instructor or bookstore.
PARTS LIST FOR THE AM RADIO SECTION (continued) MISCELLANEOUS Qty. Description Part # Qty. Description Part # r r r r r r r r r r r PC board, transistor audio amplifier PC board, main Switch Battery holder Speaker Header male 4-pin Speaker pad Knob (dial) Knob (pot) Earphone jack with nut Radio stand 510007 517055 541023 590096 590102 591004 780128 622040 622050 622130 626100 r r r r r r r r r r r Earphone Screw M1.8 x 7.5mm (battery holder) Screw M2.5 x 7.5mm (dial) Screw M2.5 x 3.
IDENTIFYING RESISTOR VALUES Use the following information as a guide in properly identifying the value of resistors. BAND 1 1st Digit Color Black Brown Red Orange Yellow Green Blue Violet Gray White BAND 2 2nd Digit Digit 0 1 2 3 4 5 6 7 8 9 Color Black Brown Red Orange Yellow Green Blue Violet Gray White Multiplier Digit 0 1 2 3 4 5 6 7 8 9 Color Black Brown Red Orange Yellow Green Blue Silver Gold Resistance Tolerance Multiplier 1 10 100 1,000 10,000 100,000 1,000,000 0.01 0.
INTRODUCTION The Elenco® Superhet 108C AM/FM Radio Kit is a “superheterodyne” receiver of the standard AM (amplitude modulation) and FM (frequency modulation) broadcast frequencies. The unique design of the Superhet 108 allows you to place the parts over their corresponding symbol in the schematic drawing on the surface of the printed circuit board during assembly. This technique maximizes the learning process while keeping the chances of an assembly error at a minimum.
CONSTRUCTION Introduction • Turn off iron when not in use or reduce temperature setting when using a soldering station. The most important factor in assembling your Superhet 108C AM/FM Radio Kit is good soldering techniques. Using the proper soldering iron is of prime importance. A small pencil type soldering iron of 25 watts is recommended. The tip of the iron must be kept clean at all times and well tinned. • Tips should be cleaned frequently to remove oxidation before it becomes impossible to remove.
SEMICONDUCTOR PARTS FAMILIARIZATION This section will familiarize you with the proper method used to test the transistors and the diode. TRANSISTOR TEST (NPN and PNP) Refer to the parts list and find a NPN transistor. Refer the Figure J (page 16) for locating the Emitter, Base and Collector. Using an Ohmmeter, connect the transistor as shown in Test A. Your meter should be reading a low resistance. Switch the lead from the Emitter to the Collector. Your meter should again be reading a low resistance.
SECTION 1A INTEGRATED CIRCUIT (IC) AUDIO AMPLIFIER This radio kit contains two separate audio systems. The first is an integrated circuit (IC) and the second is a five-transistor circuit. The objective is to show you how these two circuits function and to compare the performance of each. We will begin the radio project by building the IC audio amplifier first. The purpose of the Audio Amplifier is to increase the audio power to a level sufficient to drive an 8 ohm speaker.
ASSEMBLY INSTRUCTIONS We will begin by installing resistor R43. Identify the resistor by its color and install as shown on page 4. Be careful to properly mount and solder all components. Diodes, transistors and electrolytic capacitors are polarized, be sure to follow the instructions carefully so that they are not mounted backwards. Check the box when you have completed each installation. Wear safety goggles during all assembly stages in this manual.
ASSEMBLY INSTRUCTIONS Battery holder 3 Screws M1.8 x 7.5 3 Nuts M1.8 ** Solder and cut off excess leads. ** Volume/S2 (50kΩ Pot / SW) with nut & washer Plastic washer Knob (pot) Figure E Nut Foil (green) side Jack Knob Nut Washer Legend (blue) side of PC board Cut off locating pin 3 Plastic washer 2 ** Solder all 5 tabs to PC board ** 1 1 - GND 2 - Tip 3 - N.C.
STATIC MEASUREMENTS POWER TEST For all measurements, connect your equipment GND to circuit GND TP15. Set your VOM (Volt-OhmMillimeter) to read 2 amps DC. Connect the meter to the circuit as shown in Figure 6. Make sure that the volume control is in the OFF position (turned fully counter-clockwise). While watching your VOM, turn the volume to the ON position (rotate clockwise until a “click” is heard). The VOM should indicate a very low current. Adjust your meter for a more accurate reading if necessary.
If you do not have an audio generator, skip the following test and go directly to Section 1B. DYNAMIC MEASUREMENTS GAIN Connect the VOM and audio generator to the circuit as shown in Figure 8. lead of your VOM to the Jumper J3. Record the AC input voltage to the amplifier here: Normally the AC gain is measured at a frequency of 1kHz. Your VOM however, may not be able to accurately read AC voltages at this frequency. Therefore, it is recommended that this test be performed at 400Hz.
If an oscilloscope is not available, skip the following test and go directly to Section 1B. AC BANDWIDTH or 2.8 divisions. This frequency is called the low frequency 3dB corner. Record your answer. Connect the oscilloscope and audio generator to your circuit as shown in Figure 9. Set the audio generator for a frequency of 1kHz and minimum voltage output. Set the oscilloscope to read 0.5 volts per division. Turn on the power and slowly increase the volume control to a comfortable level.
MAXIMUM POWER OUTPUT The maximum power output before distortion due to “clipping” can be calculated using the voltage Vclp obtained in the Distortion Step as follows: Clipped Vpeak (Vp) = Vclp/2 Vroot mean squared (Vrms) = Vp x 0.7 Max power out = (Vrms)2/8 ohms = (Vclp x 0.35)2/8 Maximum power output should be greater than 200 milliwatts. Figure 10 EFFICIENCY By measuring the DC power taken from the battery at the maximum power output level, the efficiency to the audio amplifier can be calculated.
If you do not have a power supply, use a 9 volt battery instead. Generator – + Power Supply GND TP15 Oscilloscope GND TP15 Figure 11 Vp = Vclp/2 Vp = ______ Vrms = Vp x 0.
SECTION 1B TRANSISTOR AUDIO AMPLIFIER If you have successfully completed the IC audio amplifier, you are now ready to build the five-transistor audio amplifier. The transistor audio amplifier is built on a separate PC board and will plug into the IC socket. It will be necessary to remove the IC from its socket. The ratio of the power delivered to the speaker and the power taken from the battery is the efficiency of the amplifier.
ASSEMBLY INSTRUCTIONS Be careful to properly mount and solder all components. Diodes, transistors and electrolytic capacitors are polarized, be sure to follow the instructions carefully so that they are not mounted backwards. Check the box when you have completed each installation. Wear safety goggles during all assembly stages in this manual. ' TP18 - Test Point Pin (see Figure A) Q11 - 2N3904 Transistor NPN (see Figure J) C46 - 0.001μF Discap (102) Q13 - JE8550 Transistor PNP (see Figure K) R46 - 3.
Remove IC from socket and install transistor audio amplifier PC board on the same socket. STATIC MEASUREMENTS POWER TEST Set your VOM (Volt-Ohm-Millimeter) to read 2 amps DC. Connect the meter to the circuit as shown in Figure 13. Make sure that the volume control is in the OFF position (turned fully counter-clockwise). While watching you VOM, turn the volume to the ON position (rotate clockwise until a “click” is heard). The VOM should indicate a very low current.
Adjust your VOM to read 9 volts and connect it as shown in Figure 14. Make sure that the battery, or a 9 volt power supply (if available), is properly connected and turn the power ON. The voltage at TP19 should be between 3 to 6 volts. If you get this reading, go on to the next test. If your circuit fails this test, turn the power OFF and check that all of the transistors are correctly inserted in the correct locations.
It is advisable to use a digital meter because of the small voltage changes in the following test. Connect your VOM to the circuit as shown in Figure 15. Set your VOM to read 1 volt DC and turn the power ON. Record the base of Q10 here: Turn the radio ON and turn the power supply ON. Increase the supply voltage until the voltage at TP19 is equal to Vo. Now increase the voltage of the supply until the voltage at TP19 decreases by 1 volt.
You may have to change scales on your VOM for the most accurate reading. Turn the power OFF. The AC voltage gain of your audio amplifier is equal to the AC output voltage divided by the AC input voltage, or 1/Vin. The gain should approximately equal the calculated gain. Generator GND TP17 GND TP17 Figure 17 If an oscilloscope is not available, skip the following test and go directly to Section 2.
MAXIMUM POWER OUTPUT Slowly decrease the frequency of the generator until the output drops to 0.7 of its original reading, 1.4Vpp or 2.8 divisions. This frequency is called the low frequency 3dB corner - the low frequency 3dB corner or (f high 3dB) - (f low 3dB). Your calculated answer should be greater than 30kHz. The maximum power output before distortion due to “clipping” can be calculated using the voltage Vclp obtained in step 4 as follows: Vpeak (Vp) = Vclp/2 Vroot mean squared (Vrms) = Vp x 0.
If you do not have a power supply, use a 9 volt battery instead. Generator – + Power Supply GND TP17 Oscilloscope GND TP17 Figure 21 Vp = Vclp/2 Vp = ______ Vrms = Vp x 0.
SECTION 2 AM DETECTOR AND AGC STAGE charge to approximately the same voltage as the negative peak of the IF signal. After conduction stops in the diode (Off Condition), the capacitors will discharge through resistors R36 and R42. The discharge time constant must be small enough to follow the audio signal or high frequency audio distortion will occur. The discharge time constant must be large enough, however, to remove the intermediate frequency (455kHz) and leave only the audio as shown in Figure 22.
ASSEMBLY INSTRUCTIONS C34 - 100μF Lytic (see Figure B) R38 - 100Ω Resistor (brown-black-brown-gold) T6 - AM IF Coil (Yellow Dot) TP3 - Test Point Pin (see Figure A) R35 - 27kΩ Resistor (red-violet-orange-gold) T8 - AM IF Coil (Black Dot) TP5 - Test Point Pin (see Figure A) D4 - 1N4148 Diode (see Figure H) C32 - 10μF Lytic (see Figure B) C38 - .01μF Discap (103) R42 - 2.2kΩ Resistor (red-red-red-gold) R36 - 3.3kΩ Resistor (orange-orange-red-gold) C33 - .02μF Discap (203) or .
DYNAMIC MEASUREMENTS AM DETECTOR AND AGC TEST Connect your VOM and RF generator as shown in Figure 24. .001μF Generator GND TP15 GND TP15 Figure 24 Set the VOM to accurately read 2 volts DC and the output of the RF generator for 455kHz, modulation, and minimum voltage output. Turn power ON and slowly increase the amplitude of set no the the generator until the voltage at TP5 just starts to drop. This point is called the AGC threshold with no IF gain.
AM DETECTOR BANDWIDTH TEST Connect your test equipment as shown in Figure 25. Set the generator at 455kHz with 80% modulation at a modulation frequency of 1kHz. Set the oscilloscope to read 0.1 volts per division. Turn the power ON and set the volume at the minimum. Increase the amplitude of the generator until the signal on the oscilloscope is 4 divisions peak to peak. Check the signal to make sure that it is free of distortion.
ASSEMBLY INSTRUCTIONS R39 - 39kΩ Resistor (orange-white-orange-gold) T7 - AM IF Coil (White Dot) C36 - .02μF Discap (203) or .022μF Discap (223) TP4 - Test Point Pin (see Figure A) Q9 - 2N3904 transistor (see Figure J) R40 - 10kΩ Resistor (brown-black-orange-gold) C37 - .02μF Discap (203) or .022μF Discap (223) R41 - 470Ω Resistor (yellow-violet-brown-gold) STATIC MEASUREMENTS Q9 BIAS Connect your VOM as shown in Figure 27. Set the VOM to read 9 volts DC and turn the power ON.
DYNAMIC MEASUREMENTS AC GAIN Connect your test equipment as shown in Figure 28. Generator Oscilloscope .001μF GND TP15 GND TP15 Figure 28 BANDWIDTH Set the generator at 455kHz, no modulation and minimum voltage output. Set the oscilloscope at 1 volt per division. The scope probe must have an input capacitance of 12pF or less or it will detune T8. Turn the power ON and slowly increase the amplitude of the generator until 4 volts peak to peak are seen on the scope.
SECTION 4 FIRST AM IF AMPLIFIER The operation of the first IF amplifier is the same as the second IF amplifier with one important difference. The gain of the first IF amplifier decreases after the AGC threshold is passed to keep the audio output constant at the detector and prevent overload of the second IF amplifier. This is accomplished by making the voltage on the base of transistor Q8 lower as the signal strength increases.
DYNAMIC MEASUREMENTS Generator Short TP3 to R38 as shown below. Oscilloscope .001μF GND TP15 GND TP15 Figure 29 AC GAIN probe to the base of Q8 and record the peak to peak level of the 455kHz signal here: Connect your test equipment as shown in Figure 29. Vb=___________Vpp. The scope probe must have an input capacitance of 12pF or less, otherwise it will detune transformer T7. Using a clip lead, short TP3 to R38 as shown.
The “difference frequency” is used as the intermediate frequency in AM radios. The collector of Q7 also contains an IF transformer (T6) tuned only to the difference frequency. This transformer rejects all frequencies except those near 455kHz. T6 also couples the 455kHz signal to the base of Q8 to be processed by the IF amplifiers. The antenna and the oscillator coils are the only two resonant circuits that change when the radio is tuned for different stations.
IMPORTANT: Before installing the antenna coil, determine if you have a 3 wire coil or a 4 wire coil. Assemble it to the PC board as shown below. Mount the antenna assembly to the PC board. r Put the tab of the first holder into the right hole and twist the tab 90°. r Put the tab of the second holder into the left hole and twist the tab 90°. Punch out one antenna shim from the front flap of the box.
ASSEMBLY INSTRUCTIONS Screw M2.5 x 7.5mm Knob Fasten the knob to the shaft of the capacitor with a screw. Rotate the knob fully clockwise. Peel off the protective backing on the label. Line up the long white lines on the label with the arrows on the PC board. Figure O PC Board Stand Insert the PC board into the stand as shown.
STATIC MEASUREMENTS Q7 BIAS Connect your VOM to the circuit as shown in Figure 30. Short TP6 to the collector of Q7 as shown. GND TP15 Figure 30 Connect a clip lead from TP6 to the collector of Q7. This short prevents Q7 from oscillating. Set the VOM to read 2 volts DC and turn the power ON. The DC voltage at TP7 should be about 1.6 volts. If the voltage in your circuit differs by more than 0.5 volts, leave the power ON and check the battery voltage. If the battery voltage is greater than 8.
AM FINAL ALIGNMENTS AM ALIGNMENT EQUIPMENT There are two different AM alignment procedures. The first alignment procedure is for those who do not have test equipment and the second is for those who do have test equipment. WITHOUT TEST It is best to use an earphone for this procedure. Make sure that the switch is in the AM position. With an alignment tool or screwdriver, turn coils L5, T6, T7 and T8 fully counter clockwise until they stop. DO NOT FORCE THE COILS ANY FURTHER.
ANTENNA ALIGNMENT Tune the radio for a station around 600kHz. With the “magic wand” place the brass end near the antenna coil as shown in Figure 32. If the signal heard at the output increases, it means that the antenna coil needs less inductance. To remove inductance, carefully slide the antenna coil along its ferrite core in the direction shown in Figure 32. Place the iron end of the “magic wand” near the antenna coil.
Set the RF generator at 455kHz, modulation of 400Hz 80% and minimum voltage out. Set the oscilloscope to read 0.1 volts per division and turn the power ON. Increase the amplitude of the generator until the oscilloscope shows a 400Hz sinewave 5 divisions or 0.5 volts pp. With an alignment tool or screwdriver adjust T6 for a peak. Reduce the generator amplitude so that 5 divisions are maintained. Adjust T7 for a peak and reduce that amplitude again if necessary.
brass end of the “magic wand” near the antenna coil. If the signal increases, it means that the antenna coil needs less capacitance. Adjust the antenna trimmer for a peak. Refer to Figure N for the location of the AM antenna trimmer. Since the adjustment of both the antenna alignment is optimized. This process sets the AM tracking of the Superhet 108. Once the antenna is properly aligned, carefully apply candle wax or glue the antenna coil to the ferrite rod to prevent it from moving as shown in Figure 33.
DC VOLTAGES The voltage readings below should be used in troubleshooting the AM section (switch at AM position). Q7 B E C TP5 (AGC) Q8 Q9 1.5 1.0 8.8 U1 1.4 B E C 1.4 0.8 8.8 B E C 1.7 1.0 9.0 TP1 1 2 3 4 5 6 7 8 1.3 0 0 0 4.5 9.0 4.4 1.3 Q10 B E C 0.7 0.06 3.1 Q13 B E C 8.4 9.0 3.7 Q11 B E C 4.2 3.7 8.4 Q14 B E C 0.6 0 3.7 Q12 B E C 3.1 3.7 0.6 TP19 4.5 3.7 Test Conditions 1. Volume set to minimum. 3. Battery voltage = 9V 2.
PARTS LIST FOR FM SECTION RESISTORS Qty. Symbol Value Color Code Part # r r r r r r r r r r r r R9, 23 R25 R3 R18, 22, 24, 26, 27 R11 R6, 15 R2, 7 R10,12,14,16,19,20,28 R1, 8 R4, 5 R13, 17, 21 R29, 30 100Ω 5% 1/4W 220Ω 5% 1/4W 470Ω 5% 1/4W 1kΩ 5% 1/4W 1.8kΩ 5% 1/4W 2.2kΩ 5% 1/4W 6.
SECTION 6 THE FM RADIO Section 6 begins the construction of the FM radio. The stages that we will build are shown in the block diagram below. We will begin with the FM Ratio Detector and work back to the FM Antenna. Each stage will be tested before proceeding to the next stage.
ASSEMBLY INSTRUCTIONS R24 - 1kΩ Resistor (brown-black-red-gold) R23 - 100Ω Resistor (brown-black-brown-gold) C21 - .01μF Discap (103) C23 - .02μF Discap (203) or .022μF Discap (223) R21 - 47kΩ Resistor (yellow-violet-orange-gold) R25 - 220Ω Resistor (red-red-brown-gold) C19 - .
STATIC MEASUREMENTS Battery GND TP15 Figure 37 FM VOLTAGE Connect your VOM as shown in Figure 37. Switch the AM/FM switch to the FM position. Set your VOM to read 9 volts DC. Turn the power ON. The voltage at this point should be between 7 and 9 volts. Turn the power OFF. If you do not get this reading, check R25, C24 and the battery voltage. TRANSISTOR CURRENT TEST GND TP15 Figure 38 Connect your VOM to the circuit as shown in Figure 38. Turn the power ON.
If you don’t have an RF generator and oscilloscope, skip to Section 7. DYNAMIC MEASUREMENTS AC GAIN The AC gain of the ratio detector is set by the AC impedance of the primary side of T4 and the current through Q6. The current is set by R20, R21 and R22. Capacitors C22 and C19 bypass the AC signal to ground. Connect your RF generator and oscilloscope to the circuit as shown in Figure 39.
METHOD #2 ALIGNMENT OF RATIO DETECTOR USING A RF GENERATOR AND OSCILLOSCOPE Turn the power ON and set the volume control to a minimum. Increase the amplitude of the sweep generator until an “S” curve is seen (refer to Figure 41). Using an alignment tool or screwdriver, adjust the blue coil T5 until the “S” curve is centered, until each half of the “S” is equal. Repeat these steps until the alignment is optimized. Turn the power OFF.
ASSEMBLY INSTRUCTIONS R17 - 47kΩ Resistor (yellow-violet-orange-gold) R19 - 10kΩ Resistor (brown-black-orange-gold) Q5 - 2N3904 Transistor (see Figure R) TP10 - Test Point Pin (see Figure Q) C20 - .01μF Discap (103) T2 - FM IF Coil (Green Dot) C18 - .01μF Discap (103) C17 - .01μF Discap (103) R16 - 10kΩ Resistor (brown-black-orange-gold) R18 - 1kΩ Resistor (brown-black-red-gold) STATIC TESTS Q5 BIAS Connect your VOM to the circuit as shown in Figure 43. Turn the power ON.
Oscilloscope Generator .001μF GND TP15 GND TP15 Figure 44 DYNAMIC MEASUREMENTS AC GAIN BANDWIDTH Connect the RF generator and oscilloscope to the circuit as shown in Figure 44. The scope probe must have an input capacitance of 12pF or less otherwise the probe will detune T3 resulting in a false reading of the AC gain. Set the generator at 10.7MHz no modulation and minimum voltage output. Set the scope to read 50mV per division and turn the power ON.
SECTION 8 FIRST FM IF AMPLIFIER The operation of the first IF amplifier is the same as the second IF amplifier except that the gain is different. The gain is set by the AC impedance of the primary side of T2 and the current in Q4. The current in Q4 is set by the resistors R12, R13 and R15. Capacitors C14 and C15 bypass the AC signal to ground. C13 and C16 are bypass capacitors from V+ to ground to prevent feedback on the V+ line. R19 is used to widen the bandwidth of the transformer T2.
If you don’t have an RF generator and oscilloscope, skip to Section 9. Oscilloscope Generator .001μF GND TP15 GND TP15 Figure 46 DYNAMIC MEASUREMENTS AC GAIN BANDWIDTH Connect the RF generator and oscilloscope and oscilloscope to the circuit as shown in Figure 46. The scope probe must have an input capacitance of 12pF or less otherwise the probe will detune T2 causing an incorrect measurement of AC gain. Set the generator at 10.7MHz no modulation and minimum voltage output.
SECTION 9 FM RF AMPLIFIER, MIXER, OSCILLATOR, AND AFC STAGE In a superheterodyne receiver, the radio waves are emitted and then mixed with the local oscillator to produce the intermediate frequency (IF). The first stage is the RF amplifier which selects a radio station and amplifies it. The second stage is the local oscillator which oscillates at a frequency 10.7MHz above the desired radio station frequency.
STATIC MEASUREMENTS Q3 BIAS GND TP15 Figure 47 With the power turned OFF, connect your VOM to the circuit as shown in Figure 47. Set your VOM to read 9 volts DC and turn the power ON. The DC voltage at the base of Q3 should be approximately 1.8 volts. If your answer varies by more than 2 volts, turn the power OFF and check components R7, R8, R11 and Q3. If you don’t have an RF generator and oscilloscope, skip to the FM Oscillator Assembly Procedure. DYNAMIC MEASUREMENTS AC GAIN Turn the power OFF.
Oscilloscope Generator .001μF GND TP15 GND TP15 Figure 48 BANDWIDTH TEST Turn the power OFF. The bandwidth can be calculated as follows: Connect your test equipment to the circuit as shown in Figure 48. Set your generator at 10.7MHz no modulation and minimum voltage output. Set the scope for 10mV per division. Turn the power ON and slowly increase the amplitude of the generator until 40mVpp are seen on the scope. Increase the frequency until the voltage drops 0.707 of its original value, 2.
STATIC MEASUREMENTS Q2 BIAS Connect your VOM to the circuit as shown in Figure 49. Set your VOM to read 9 volts and turn the power ON. The voltage at the base of Q2 should be about 4 volts. Turn the power OFF. If you do not get this measurement, check R4, R5 and Q2. GND TP15 Figure 49 AFC diode called a varactor. A varactor will change its internal capacitance when a voltage is applied. The ratio detector diodes are positioned in such a way that when the 10.
If you don’t have an RF generator, skip to the RF Amplifier Assembly Procedure. Generator .001μF GND TP15 GND TP15 Figure 50 Connect the RF generator and VOM to the circuit as shown in Figure 50. Set your VOM to read 9 volts DC. Set your generator at 10.7MHz no modulation and moderate signal strength output. Turn the power ON. Record the voltage of D1 here: Increase the frequency of the generator until the voltage is equal to V(D1). While watching your VOM, increase the frequency of your generator.
STATIC MEASUREMENTS Q1 BIAS Connect your VOM to the circuit as shown in Figure 51. Set your VOM to read 9 volts and turn the power ON. The voltage at the base of Q1 should be about 1.6 volts. If you do not get this reading, check R1, R2, R3 and Q1. Turn the power OFF. GND TP15 Figure 51 ANTENNA FM ASSEMBLY Antenna FM 2 Screw M2 x 5mm (antenna) 2½” Wire #22AWG Insulated (extra wire in AM Section) (see Figure W) Threaded holes Mount the antenna to the PC board with two screws as shown.
ALIGNMENT WITH NO TEST EQUIPMENT With an alignment tool or screwdriver turn coils T1, T2 and T3 fully counter-clockwise. DO NOT FORCE THE COILS ANY FURTHER. Turn each coil in about 1¼ to 1½ turns. IF ALIGNMENT GND TP15 Figure 52 With an alignment tool or screwdriver turn coils T1, T2 and T3 fully counter-clockwise. DO NOT FORCE THE COILS ANY FURTHER. Turn each coil in about 1¼ to 1½ turns. Use the earphone provided for best results. Switch to the FM position.
is heard. Place the iron end of the “magic wand” near L3. If the station is heard, it means that L3 needs less capacitance. Carefully adjust the FM oscillator trimmer located on the back of the gang until the station is heard. Repeat this step until the pointer is aligned to the station’s frequency. Adjusting both the oscillator coil L3 and the oscillator trimmer capacitor will effect the oscillator’s frequency, so it is advisable to repeat this procedure until the FM oscillator alignment is optimized.
OSCILLATOR ALIGNMENT RF ALIGNMENT Remove the clip lead and set your generator at 88MHz modulator at 1kHz, 22.5kHz deviation and minimum voltage output. Tune the radio until a 1kHz signal is seen on the scope. It may be necessary to increase the amplitude of the generator. Rotate the dial until the white pointer is aligned to 88MHz. Using the “magic wand” place the brass end near L3 as shown in Figure 53. If the signal seen on the scope increases, this means L3 needs less inductance.
DC VOLTAGES The voltage readings below should be used in troubleshooting the FM section (Switch at FM position.) Q1 B E C 1.6 .9 7.0 Q4 B E C 3.3 3.0 7.1 Q5 B E C 1.3 .7 7.5 B E C 1.3 .6 7.5 Test Conditions 1. Volume set to minimum. Q2 2. Connect TP14 to TP15 with a jumper wire. 3. Battery voltage = 9V Q3 B E C 1.6 1.3 7.0 Q6 B E C 1.2 .6 6.6 4. All voltages are referenced to circuit common. 5.
QUIZ - FM RADIO SECTION INSTRUCTIONS: Complete the following examination, check your answers carefully. 1. The FM broadcast band is . . . r A) 550 - 1,600kHz. r B) 10.7MHz. r C) 88 - 108MHz. r D) 98.7 - 118.7MHz. 6. The ratio detector is used because ... r A) it is sensitive to noise. r B) it is insensitive to noise. r C) it provides amplification. r D) it doesn’t need a filter. 2. The maximum audio frequency used for FM is ... r A) 7.5kHz. r B) 15kHz. r C) 20kHz. r D) 10.7MHz. 7.
AM/FM-108 Radio Baffle it creates positive pressure on the air in front of it and negative pressure on the rear. At low frequencies, out of phase front and rear waves mix causing partial or total cancellation of the sound wave. The end result is a speaker less efficient and distorted. NOTICE: Keep the box the kit came in. After you have completed the radio and it operates satisfactorily, you may want to install a baffle to improve the sound.
3. Bend the top side upward as shown. 4. Bend the two sides upward. Attach the three sides using scotch tape or glue (Elmer’s, Duco Cement, or other). 5. Bend the bottom side upward and attach it to the other sides using scotch tape or glue. Bend the two mounting flaps down. Side View 6. Place the baffle over the speaker. Align the mounting holes and attach it using the two screws and two nuts supplied. The screws should go through the X mark on the baffle flap.
SCHEMATIC DIAGRAM - AM/FM RADIO ELENCO® 150 Carpenter Avenue Wheeling, IL 60090 (847) 541-3800 Website: www.elenco.com e-mail: elenco@elenco.
