Ramsey Electronics AM1 Guía del usuario

AM1 •1

AM BROADCAST

TRANSMITTER KIT

Ramsey Electronics Model No. AM1

Ever want to be your own disc jockey or talk show host ? Build

and run your own AM broadcast station with this exciting kit !

The AM1 transmitter is designed specifically for simplicity of

construction and use - an ideal first kit !

•Great for transmitting your tape deck, CD player, or voice

throughout the house, yard, or car !

•Powerful enough for high school, college, or neighborhood radio

station - in use the world over !

•Easily tunes to any clear channel on the AM broadcast band. - from

530 to 1750 KHz.

•Operates on the same principle as the “big-boys”, learn how

commercial transmitters work as well !

•Superior performance - transmits up to 1/4 mile !

•Adjustable input level - can be configured for line level or

microphone input.

•Unit runs on 9 - 12 volts DC.

•Handy information on FCC rules and antenna hints.

•Complete and informative instructions guide you to a kit that works

the first time, every time - enhances resale value, too !

AM1 •2

PARTIAL LIST OF AVAILABLE KITS

RAMSEY TRANSMITTER KITS

• FM10A FM Stereo Transmitter

• MP3FM Synthesized MP3 Transmitter

• FM25 Synthesized FM Stereo

Transmitter

• AM25 Synthesized AM Transmitter

• AM1 AM Transmitter

RAMSEY RECEIVER KITS

• FR1 FM Broadcast Receiver

• AR1 Aircraft Band Receiver

• AA7 Active Antenna

• SC1 Shortwave Converter

RAMSEY HOBBY KITS

• SG7 Personal Speed Radar

• SS70 Speech Scrambler

• TT1 Telephone Recorder

• SP1 Speakerphone

• MD3 Microwave Motion Detector

• PH10 Peak hold Meter

• LC1 Inductance-Capacitance Meter

RAMSEY AMATEUR RADIO KITS

• FX 146 VHF Transceiver

• HR Series HF All Mode Receivers

• QRP Series HF CW Transmitters

• CW7 CW Keyer

• CPO3 Code Practice Oscillator

• QRP Power Amplifiers

RAMSEY MINI-KITS

Many other kits are available for hobby, school, scouts and just plain FUN. New

kits are always under development. Write or call for our free Ramsey catalog.

AM1 AM BROADCAST TRANSMITTER KIT INSTRUCTION MANUAL

Ramsey Electronics publication No. MAM1 Revision 1.2 First printing: August, 1994

written permission of Ramsey Electronics, Inc. Printed in the United States of America.

AM1 •3

AM BROADCAST

TRANSMITTER AM1

Ramsey Publication No. MAM1

Manual Price Only $5.00

TABLE OF CONTENTS

Introduction to the AM1................. 4

AM1 Circuit Description ................ 4

Schematic Diagram....................... 6

Parts Layout Diagram ................... 7

Parts List ........................................ 8

Assembly Instructions ................... 9

Antenna Considerations............... 13

Alignment Procedures.................. 14

Experimental Broadcasting .......... 14

Troubleshooting ........................... 15

FCC Information........................... 16

Antenna Experimenting................ 18

Ramsey Kit Warranty ................... 19

KIT ASSEMBLY

AND INSTRUCTION MANUAL FOR

RAMSEY ELECTRONICS, INC.

793 Canning Parkway

Victor, New York 14564

Phone (716) 924-4560

Fax (716) 924-4555

AM1 •4

INTRODUCTION

Many times we wish to be heard via wireless communications. Whether

transmitting music or voice, what’s required is a stable transmitter tunable to

an unused frequency on the broadcast band. Here at Ramsey, we have

produced several models of FM wireless units for years. Recent requests for

an AM type transmitter have been answered with this kit.

The Ramsey AM1 transmitter is a true broadcast transmitter, which any

person may build and use in accordance with the rules of one’s national

telecommunications authority. For U.S. residents, that authority is the

Federal Communications Commission (FCC). The AM1’s low power

broadcasting capabilities make it practical for many uses, but one should

remember that this transmitter is definitely not a toy. We will refer to the FCC

regulations frequently in this manual and provide you with some information

necessary to enjoy the AM1’s capabilities in accordance with the law.

Typical uses for the AM1 include:

•Student operated school radio stations.

•Re-broadcasting received audio for shortwave or HAM radio use.

•Listening aid for auditoriums, churches, or other events.

•Short range experimentation.

We think that you will be very pleased with the transmitting range, audio

quality, and frequency stability of this build it yourself AM transmitter. If you

follow our assembly instructions carefully and use your AM1 in accordance

with applicable FCC rules, a whole new world of sharing news, views, and

music with friends and neighbors awaits you.

AM1 CIRCUIT DESCRIPTION

Before we dive into the circuit description of the AM transmitter, first we’ll

describe exactly what we mean when we say “AM”. An (A)mplitude (M)

odulated signal is actually a combination of two signals. The high frequency

carrier is the frequency that one will tune on the radio receiver’s dial, from

530 to 1750 KHz. The modulation is the audio information that rides “on top”

of the high frequency carrier, resulting in a changing of the level, or

amplitude, of the output waveform. Take a glance at the schematic and

follow along at how we produce this AM waveform.

The RF oscillator consists of Q6 and associated components. The

frequency of operation is determined by selecting the proper values for C9

and C10, and adjusting the inductance of coil L2. The “buffer” amplifier (Q5)

is connected to the base of Q6 in order to use the undistorted oscillator

AM1 •5

output for the RF carrier frequency.

The audio input path is routed from J1, the audio input source, to transistor Q2

to amplify the incoming signal. Notice that the transistor is biased to be linear

using resistors R3, R5, and R6. The incoming audio signal is therefore

amplified undistorted (for great sounding audio). Optional capacitor C4 is used

only when a microphone input is used to provide additional gain from transistor

Q2. The audio input level to the amplifier can also be adjusted using R12, the

input level adjustment.

The resulting audio output is fed to transistor Q1, which does not provide any

gain, but supplies enough current to modulate the RF carrier. Inductor L1

allows the low frequency audio to pass through but “chokes” the RF signal and

does not allow it to get “back into” the audio circuitry.

Transistors Q3 and Q4 comprise the “power amplifier” section of the circuit.

Their collector supply voltage is furnished by Q1, thus producing an AM output

waveform. This signal is then low pass filtered using C13, C14, and L3.

Notice also that the audio information is applied at the power amplifier stage.

This is referred to as “high level” modulation, and is commonly used for high

power AM broadcast stations. The distinct advantage to this is that the RF

amplifiers need not be biased for linear operation. It is much cheaper to

manufacture a linear amplifier for the relatively low frequency audio, than to

produce the AM waveform at a low level and amplify it to a higher power level

without distortion. The main disadvantage of high level modulation is that the

audio modulator’s power must be half that of the final transmitter, not too tough

for our low power kit, but try to imagine the amplifier for a 50,000 watt AM

broadcast station! Boy, that audio amp would sure crank the ‘ol car stereo!

It should also be stated that, due to the linear operation of the amplifiers in this

circuit (transistors Q1 and Q2 biased “on”), this circuit will consume some

power. It is not recommended that a common rectangular 9V battery be used

to power this kit. Instead, a battery “pack” consisting of eight 1.5 volt cells, a

12V sealed battery, or other external 12V DC supply may be used.

Low Frequency Audio Waveform

High Frequency Radio Carrier

Amplitude Modulated Signal

AM1 •6

PARTS LAYOUT DIAGRAM

AM1 •7

PARTS LIST

Please verify that the following items are in your kit before beginning

assembly.

RESISTORS

4 270 ohm [red-violet-brown] (R6,7,9,11)

2 1K ohm [brown-black-red] (R5,10)

1 2.2K ohm [red-red-red] (R1)

4 10K ohm [brown-black-orange] (R2,3,4,8)

1 5K PC mount potentiometer [marked 502] (R12)

CAPACITORS

1 220 pF disc capacitor [marked 220 or 221] (see text C9,10,16)

1 470 pF disc capacitor [marked 470] (see text C9,10,16)

1 .001 µF disc capacitor [marked .001 or 102] (see text C9,10,16)

4 .002 or .0022 µF disc capacitor [marked .002,.0022 or 2000,2200]

(C13,14, see text C9,10,16)

7 .01 µF disc capacitor [marked .01 or 103 or 10nF] (C3,5,6,7,8,11,12)

3 10 µF electrolytic capacitors (C1,2,4)

1 220 µF electrolytic capacitor (C15)

INDUCTORS

1 48 µH inductor [enameled copper wire wound on ferrite core] (L1)

1 10 µH inductor [marked 100] (L3)

1 slug tuned variable inductor [fine wire wound on plastic and

cardboard cylinder] (L2)

SEMICONDUCTORS

6 NPN transistors [marked 3904] (Q1,2,3,4,5,6)

MISCELLANEOUS PARTS AND HARDWARE

2 RCA type PC mount connectors (J1,2)

1 2.5mm power jack (J3)

1 DPDT pushbutton switch (S1)

1 AM1 printed circuit board

1 “diddle stick” plastic alignment tool

AM1 •8

ASSEMBLY INSTRUCTIONS

There are numerous solder connections on the AM1 printed circuit board.

Therefore, PLEASE take us seriously when we say that good soldering is

essential to the proper operation of your transmitter!

•Use a 25-watt soldering pencil with a clean, sharp tip.

•Use only rosin-core solder intended for electronics use.

•Use bright lighting, a magnifying lamp or bench-style magnifier may

be helpful.

•Do your work in stages, taking breaks to check your work. Carefully

brush away wire cuttings so they don't lodge between solder

connections.

We have a two-fold "strategy" for the order of the following kit assembly

steps. First, we install parts in physical relationship to each other, so there's

minimal chance of inserting wires into wrong holes. Second, whenever

possible, we install in an order that fits our "Learn-As-You Build" Kit building

philosophy. This entails describing the circuit that you are building, instead of

just blindly installing components. We hope that this will not only make

assembly of our kits easier, but help you to understand the circuit you’re

constructing.

For each part, our word "Install" always means these steps:

1. Pick the correct part value to start with.

2. Insert the part, oriented correctly, into its correct holes in the PC-

board.

2. If helpful, gently BEND the part's wire leads or tabs to hold it into

place, with the body of the part snugly against the top side

("component side") of the PC-board. The top side is the

side that does not contain metal traces, but does have an

outline of each part printed on it.

3. Insert it into the correct PC board location.

4. Orient it correctly, follow the PC board drawing and the written

directions for all parts - especially when there's a right way

and a wrong way to solder it in. (Diode bands, electrolytic

capacitor polarity, transistor shapes, dotted or notched ends

of IC's, and so forth.)

AM1 •9

5. Solder all connections unless directed otherwise. Use enough

heat and solder flow for clean, shiny, completed connections.

6. Trim or nip all excess wires extending beyond each solder

connection, taking care that wire trimmings do not become lodged in

PC-board solder connections.

Now, let's get building!

Since you may appreciate some “warm-up” soldering practice as well as a

chance to put some “landmarks” on the PC board, we’ll first install some

“hardware” components. This will also help us to get acquainted with the up -

down, left - right orientation of the circuit board. Remember that the

components will be mounted on the “component” (printed) side of the circuit

board and then soldered on the “solder” (foil) side of the circuit board.

1. Install DPDT switch S1. Position it so that the plunger of the switch

extends over the edge of the PC board. Be sure to push the switch flat

to the circuit board. Solder all six connections.

2. Install RCA phono jacks J1 and J2. These connectors will “snap” into

place before soldering. Don’t be afraid to completely solder all three

ground connections as these will also limit the “stress” on the input and

antenna connections.

3. Install the 2.5 mm power connector in the J3 position.

We’ll now begin to construct the RF oscillator section of the AM1. Be sure to

mount the components as close as possible to the PC board to avoid

“radiating” any unwanted signals due to long lead lengths.

4. Install L2, the slug tuned inductor. Solder all three tabs.

5. Install C8, .01 µF disc capacitor [marked .01 or 103 or 10nF].

6. Install R8, 10K ohm [brown-black-orange].

7. Install C6, .01 µF disc capacitor [marked .01 or 103 or 10nF].

8. Identify Q6, a 2N3904 NPN transistor. When installing Q6, observe

correct placement of the flat side. Press the transistor snugly into the PC

board so that only a minimum amount of wire lead is exposed above the

board. In soldering, do not be afraid of using enough heat to make a

good solid connection.

9. Install R11, 270 ohm [red-violet-brown].

10. Install R7, another 270 ohm [red-violet-brown].

AM1 •10

11. Install Q5, a 2N3904 transistor. Be sure to orient it correctly! See the

parts diagram for correct orientation.

12. Install C7, .01 µF disc capacitor [marked .01 or 103 or 10nF].

13. Install R9, 270 ohm [red-violet-brown].

14. Install C15, 220 µF electrolytic capacitor. Electrolytic capacitors are

polarized with a (+) and a (-) lead and must be installed in the correct

orientation. Ordinarily, only the negative side is marked on the capacitor

body with a dark band and the (-) sign clearly shown, while PC boards

will usually show the (+) hole location. Use care to ensure proper

polarity.

Whew ! Now that wasn’t so bad was it? You have just completed most of the

oscillator. Notice that we have excluded a few capacitors, C9, 10, and 16.

We will install these later while testing the unit. Take a moment now to

recheck your work for clean, shiny solder connections. Resolder any

connections that are less than perfect.

We’ll get back to building now, starting at the audio input and working

through the audio circuitry.

15. Install trimmer potentiometer R12. Solder all three leads.

16. Install C2, 10 µF electrolytic capacitor. Be sure to orient the part

correctly. See the parts placement diagram for correct orientation.

17. Install R5, 1K ohm [brown-black-red].

18. Install C12, .01 µF disc capacitor. This capacitor act as a RF bypass

component. It effectively “shorts” the high frequency signals to ground

while not effecting the low frequency audio.

19. Install Q2, 2N3904 NPN transistor [marked 2N3904]. Pay attention to

the orientation!

20. Install R3, 10K ohm [brown-black-orange].

21. Install R1, 2.2K ohm [red-red-red].

22. Install R2, 10K ohm [brown-black-orange].

23. Install R6, 270 ohm [red-violet-brown].

24. Install C1, 10 µF electrolytic capacitor. Watch the polarity!

25. Install R4, 10 K ohm [what colors were those ??!!] [brown-black-

orange].

26. Install C11, .01 µF disc capacitor [marked .01 or 103 or 10nF].

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