Elenco FM Wireless Microphone Kit User Manual

FM WIRELESS MICROPHONE KIT

MODEL K-30/AK-710

ight © 2006, 1994 b

yr

Cop

t of this book shall be reproduced b

No par

Assembly and Instruction Manual

Elenco®Electronics, Inc.

y Elenco

®

Electronics

y means; electronic, photocopying, or otherwise without written permission from the publisher.

y an

, Inc.

ights reser

All r

ved. Revised 2006 REV-J 753016

PARTS LIST

If you are a student, and any parts are missing or damaged, please see instructor or bookstore.
If you purchased this kit from a distributor, catalog, etc., please contact Elenco®Electronics (address/phone/e-mail is at the
back of this manual) for additional assistance, if needed. DO NOT contact your place of purchase as they will not be able
to help you.

RESISTORS

Qty. Symbol Value Color Code Part #

1 R5 150Ω 5% 1/4W brown-green-brown-gold 131500
2 R8, R10 1kΩ 5% 1/4W brown-black-red-gold 141000
1 R7 1.5kΩ 5% 1/4W brown-green-red-gold 141500
1 R3 4.7kΩ 5% 1/4W yellow-violet-red-gold 144700
1 R1 8.2kΩ 5% 1/4W gray-red-red-gold 148200
1 R6 10kΩ 5% 1/4W brown-black-orange-gold 151000
1 R2 27kΩ 5% 1/4W red-violet-orange-gold 152700
2 R4, R9 47kΩ 5% 1/4W yellow-violet-orange-gold 154700

CAPACITORS

Qty. Symbol Value Description Part #

1 C4 10pF (10) Discap 211011
1 C5 12pF (12) Discap 211210
1 C6 33pF (33) Discap 213317
2 C3, C7 .001
2 C1, C2 .1

µF (102) Discap 231035

µF (104) Discap 251010

SEMICONDUCTORS

Qty. Symbol Value Description Part #

3 Q1 - Q3 2N3904 Transistor 323904
1 LED Light Emitting Diode (LED) 350001
1 Coil FM Mic 468751

MISCELLANEOUS

Qty. Description Part #

1 PC Board 517710
1 Switch (S1) 541024
1 Mic 568000
1 Battery Clip (+) 590091
1 Battery Clip (–) 590093
1 Foam Cover 620002
1 Top Case 623105
1 Bottom Case 623205
1 Stand 626010

Qty. Description Part #

1 Battery Cover 627002
1 Alignment Tool 629011
1 Screw 2.5mm x 4mm 641310
3 Screw 2.6 x 8mm 642109
12” Wire 22ga. Gray 814810
6” Wire 26ga. Black 816210

10.5” Wire 26ga. Red 816220
1 Solder Tube 9ST4

Caution: Do not mix alkaline, standard (carbon-zinc), or rechargeable (nickel-cadmium) batteries.

PARTS IDENTIFICATION

Resistor

Capacitor Transistor

SwitchLED

Stand

Battery Cover

FM Coil

Microphone

Battery Clips

-1-

Case

To p

(–)(+)

Bottom

IDENTIFYING RESISTOR VALUES

Use the following information as a guide in properly identifying the value of resistors.

BAND 1

1st Digit

Color Digit
Black 0
Brown 1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Gray 8
White 9

BANDS

BAND 2

2nd Digit

Color Digit
Black 0
Brown 1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Gray 8
White 9

1

IDENTIFYING CAPACITOR VALUES

Multiplier

Color Multiplier
Black 1
Brown 10
Red 100
Orange 1,000
Yellow 10,000
Green 100,000
Blue 1,000,000
Silver 0.01
Gold 0.1

2 Multiplier Tolerance

Resistance

Tolerance

Color Tolerance
Silver +
Gold +5%
Brown +1%
Red +2%
Orange +3%
Green +
Blue +0.25%
Violet +0.1%

10%

0.5%

Capacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or µF (microfarads). Most
capacitors will have their actual value printed on them. Some capacitors may have their value printed in the following
manner. The maximum operating voltage may also be printed on the capacitor.

10µF 16V

Multiplier

The value is
10 x 1,000 =
10,000pF or
.01µF 100V

For the No.01234589
Multiply By 1 10 100 1k 10k 100k 0.01 0.1

Note: The letter “R” may be used at times
to signify a decimal point; as in 3R3 = 3.3

The letter M indicates a tolerance of +
The letter K indicates a toler
The letter J indicates a toler

103K

100V

First Digit
Second Digit
Multiplier

olerance

T

Maximum Working Voltage

20%

ance of +10%

ance of +5%

FM MICROPHONE KIT

Your FM Microphone is really a miniature frequency
modulated transmitter operating in the standard FM

ange of frequencies f

broadcast band.
FM broadcast band is 90MHz (MHz = Megahertz or
90 million cycles per second). Because the FM
microphone has a variable tuned circuit, it can be
tuned to a quiet spot on your local FM broadcast
band for the best reception. When the small

The r

or the

microphone element is struck by sound, it converts
the audio to a change in current through resistor R1
(see schematic diag
amplified and eventually frequency modulates the
transmitter. The transmission range of the FM
microphone is approximately 100 feet, depending
on the efficiency of the antenna (properly tuned or
not) and the quality of the FM radio receiver.

r

This electr

am).

ical change is

-2-

BASIC MODULATION THEORY

There are many different methods for modulating
information onto a radio wave. The two most
popular methods are Amplitude Modulation (AM)
and Frequency Modulation (FM). Figure 1 shows
the basic difference between these two methods. In
an amplitude modulated radio wave, the audio
information (voice) varies the amplitude of the RF
carrier. To recover this information, all that is
needed is a peak detector that follows the carrier
peaks. This is fairly easy to understand. In a
frequency modulated radio wave, the information
changes the frequency of the carrier as shown in
Figure 1.

Amplitude Modulation

Frequency Modulation

Figure 1

The amplitude of the radio frequency carrier wave
remains constant.
determines how far the frequency is moved from the
unmodulated carrier frequency. In a normal FM
radio broadcast, the maximum deviation from center
frequency is set at +
A soft sound ma

umber of times the carrier deviates from the

The n
center frequency, each second depends on the
frequency of the audio. For example, if the carrier is
moved to +75kHz, then –75kHz 1,000 times each
second, the carr
with a 1,000 cycle audio tone.

One advantage of FM modulation over AM
modulation is the carrier amplitude is not important
since the information is carried by the frequency.
This means that an
signal after transmission (such as lightning, spark or
ignition noise in cars, etc.) can be reduced by
allowing the amplifiers before detection to limit or
saturate. This principle is shown in Figure 2.

The loudness of the audio

150kHz for the loudest sound.

y move the carrier only +10kHz.

ier is 50% modulated f

or loudness

y amplitude noise added to the

broadcast band has only 7,000 Hertz band width
(Figure 3). The FM band is therefore considered to
be “High Fidelity” compared to the older AM band.

Original Transmitted

Signal

Received Signal with

Noise and Fading

Received Signal

After Limiting

Amplifier

Figure 2

Audio Bandwidth for AM & FM

Narrow Band

Wide

Bandwidth

7kHz 25kHz

AM Broadcast Band FM Broadcast Band

Figure 3

Another big advantage that FM has over AM is the
“Capture” effect in FM broadcast. If two different
broadcasts are very close in frequency or on the
same frequency in AM, they will produce an audio

eet or beat.

tw
strongest signal and ignore the weaker one. In
other words, if a local transmitter and another
distant tr
FM receiver will lock in on the strong local station
and reject the w
conditions e
between the two stations, which is very annoying.

Capture works because the receiver “sees” radio

ves as the sum of each frequency present. Since

a

w
FM only looks at frequency
be eliminated b
The detector “sees” only the strong signal after the
limiting amplifier has stripped the weak one away.

o Frequencies

w

T

Transmitted

In FM, the receiver will “Capture” the

ansmitter are on the same frequency, the

eak one. In an AM radio, if the same

xist, you will hear a beat (a whistle)

, the weaker signal can

y the limiter as shown in Figure 4.

What Limiter “sees” Capture Effect

Output from limiter
F1 only . . . F2 removed

The standard broadcast band f

or FM w

as also
designed to have an audio range up to 25,000 Hertz
(Hertz = cycles per second). The standard AM

F1 F2 F1 + F2 Limiter Levels

Figure 4

-3-