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FM25A 

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Ramsey Electronics Model No.           FM25A 

Own and operate your own FM Stereo broadcast station.  
Definitely not a toy, the FM-25A has an exceptional synthesized 
transmission range and improved audio quality that puts your 
favorite radio station to shame. 

Great for transmitting your tape deck or CD player throughout the 
house, yard or even your car. 

Powerful enough for college or neighborhood radio stations - in use 
all over the world. 

Fantastic improved audio quality, sounds better than most stations 
on the dial.  And we’ll tell you why! 

Easily connects to the line-level outputs on any tape deck, stereo 
system or CD player. 

Some users hook up one channel to the scanner and the other to 
their two way radio.  Now you can hear what’s going on around town 
or a couple blocks away from your house with a simple stereo 
receiver... and adjust the volume of each individually with your 
balance control! 

Add a mike-mixer and tape or CD deck for a “PRO” sounding radio 
station. 

Operates on 8 to 14 volts DC, 12 volt DC power supply provided. 

Easily tunable anywhere in the 88-108 MHz FM band. 

Clear, concise instructions guide you step-by-step to a finished 
product that works FIRST time. 

SYNTHESIZED FM 
STEREO TRANSMITTER 

Summary of Contents for FM25A

Page 1: ...on the dial And we ll tell you why Easily connects to the line level outputs on any tape deck stereo system or CD player Some users hook up one channel to the scanner and the other to their two way radio Now you can hear what s going on around town or a couple blocks away from your house with a simple stereo receiver and adjust the volume of each individually with your balance control Add a mike m...

Page 2: ...ITS 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 SYNTHESIZED FM STEREO TRANSMITTER KIT INSTRUCTION MANUAL Ramsey Electronics p...

Page 3: ...agram 16 Case and Knob Assembly 18 Choosing an Operating Frequency 19 Adjusting and Alignment 19 At Home Use 21 Projects and Experiments 21 Antenna Ideas 22 Troubleshooting 23 FCC Rules and Information 24 Understanding Field Strength 26 Summary 28 Warranty 31 KIT ASSEMBLY AND INSTRUCTION MANUAL FOR RAMSEY ELECTRONICS INC 793 Canning Parkway Victor New York 14564 Phone 716 924 4560 Fax 716 924 4555...

Page 4: ...uency stability and stereo channel separation of this build it yourself synthe sized FM stereo transmitter If you follow our assembly directions carefully and use your FM25A in accordance with applicable FCC rules a whole new world of sharing music news and views with friends and neighbors awaits you Since the sharing of music and information is vital to the culture of our late 20th century global...

Page 5: ... the transmitted frequency feedback for the PLL to compare the crystal frequency to It is also fed to Q2 through C29 and R19 Q2 provides further am plification before the signal goes to the low pass filter The low pass RF filter consisting of C35 L2 C36 L3 and C37 allows us to pass the fundamental operating frequency while rejecting the harmonics Harmonics are multiples of the fundamental frequenc...

Page 6: ...ng the FM25A s out put frequency back on frequency If the desired frequency is higher than the ref erence pin 13 is driven low If the frequency is just right then pin 13 becomes a high impedance basically disconnecting it from the circuit so it will cause no change in the voltage on D21 The voltage changes on pin 13 are filtered by R8 C16 R10 and C19 to provide a steady noise free tuning voltage f...

Page 7: ...FM25A 7 FM25A PARTS LAYOUT DIAGRAM ...

Page 8: ...c capacitor C4 1 1000 µF electrolytic capacitor C5 Resistors 1 100 ohms brown black brown R12 2 220 ohms red red brown R14 17 1 270 ohms red violet brown R13 2 470 ohms yellow violet brown R2 R10 1 1K ohms brown black red R31 3 2 2K ohms red red red R9 R19 R15 2 3 3K ohms orange orange red R9 R15 3 4 7K ohms yellow violet red R21 R28 R30 9 10K ohms brown black orange R1 R4 R5 R18 R20 R23 R24 R25 R...

Page 9: ... power jack J1 1 Horizontal push button switch S1 1 Small black mini push button switch S2 3 DIP switches 8 pin dip with 4 sliding tabs S3 S4 S5 1 Whip antenna ANT1 1 12 volt DC power transformer 1 Two pin jumper and jumper block JMP1 Required not supplied Shielded stereo audio cables Line level audio source such as a tape deck or CD player Case and Knob Parts Top Cover Bottom Base Tray 4 Short Ph...

Page 10: ...t jacks to antenna as faithfully as is practical as part of Ramsey s Learn As You Build kit assembly philosophy FM25A ASSEMBLY Use the boxes to check off your progress Check all received parts against the Parts list on page 8 and 9 The parts list describes the various markings that may be found on the kit parts Since you may appreciate some warm up soldering practice as well as a chance to put som...

Page 11: ...e been inserted Bend the two corner pins to hold it in place while you are soldering After soldering make sure that it is flat on the board Solder all 16 pins and then CAREFULLY check to ensure you have not caused any solder bridges between pins 8 Now that the IC socket has your prime attention carefully insert the mi crocontroller IC U2 marked with a white sticker into the socket taking gentle ca...

Page 12: ...resistors set the pre emphasis characteristic for the FM25A Pre emphasis is a tech nique used in FM transmitters to increase the high frequency signal to noise ratio 7a Install R9 3 3K orange orange red 8a Install R15 3 3K orange orange red 9a Install C14 022 µF disc capacitor marked 022 or 223 10a Install C22 022 µF disc capacitor marked 022 or 223 Electrolytic capacitors have a right and wrong w...

Page 13: ...apacitor marked 220 or 221 or 220K 5c Install C34 10µF electrolytic capacitor Observe polarity 6c Install C28 001 µF disc capacitor marked 001 or 102 7c Install C12 a 001 µF disc capacitor marked 001 or 102 8c Install C18 5 pF disc capacitor marked 5 or 5K 9c Install C20 5 pF disc capacitor marked 5 or 5K 10c Install C15 01 µF disc capacitor marked 01 or 103 or 10 nF 11c Install R7 100K ohms brown...

Page 14: ...ly careful when in stalling this part as its leads are very small You may elect to put a small dab of glue on the part to relieve stress and to keep it firmly attached to the PC board or use a piece of clipped off lead and form a loop to go around the crystal and through the holes in the board 27c Install JMP1 a 2 pin header A jumper block will be installed on this to enable stereo transmission RF...

Page 15: ...apacitor marked 47 or 47K Synthesizer 1f Install C26 001 µF disc capacitor marked 001 or 102 or 1 nF 2f Install R12 100 ohms brown black brown Note this part is a laydown 3f Install R23 10K ohms brown black orange 4f Install R24 10K ohms brown black orange 5f Install R25 10K ohms brown black orange 6f Install R26 10K ohms brown black orange 7f Install D9 D20 small glass diodes The banded ends go t...

Page 16: ... sure will also hide a number of not so pretty assembly mistakes Once the kit is enclosed your friends will never know that you were new to soldering Finally the enclosure will protect your electronics from many possible causes of damage so that you can receive years worth of enjoyment using talking about and remem bering the fun you had building your kit In short TAKE YOUR TIME when as sembling t...

Page 17: ...rd broadcasting frequencies In order to comply with Part 15 of FCC regulations it is your responsibility to determine carefully that your opera tion will not cause interference to broadcast reception Please study Appendix A of this manual before using your FM25A ADJUSTING YOUR FM25A TRANSMITTER Keep all tests very brief until you have carefully chosen an open operating fre quency in the FM broadca...

Page 18: ...out half otf their rotation This is a good starting position The best audio input for both testing and general operation are the stereo line level outputs of a cassette deck or CD player Most stereo systems have a variety of auxiliary output jacks of which one or more are line level outputs Hooking up an audio source to your FM25A is really quite simple However there are some general rules A terri...

Page 19: ...your effort will be concen trated on smoothly managing or mixing the audio signals fed into the transmit ter input Operation of the transmitter itself consists simply of the following 1 Correct construction and adjustment 2 Carefully checking for an open frequency between 88 108 MHz in accor dance with FCC Rules Part 15 3 Setting up a suitable antenna 4 Connecting the audio source to the Left and ...

Page 20: ...reat difference in antenna length from 88 to 107 MHz Some antenna designers have the view that an approximate dipole such as 2 5 ft on a side will do fine while others believe it is worth the effort to calculate the length for your exact frequency using the simple formula of Length of one side in feet 234 Frequency in MHz If the dipole is installed vertically the end connected to the center conduc...

Page 21: ...home or building Do not attempt such an installation unless you know exactly what to do and not to do Also because such an installation is be yond the original purpose of this kit and the safety standards intended for all Ramsey kits and because we have not tested the FM 25 in such an installa tion we cannot provide further details for such an installation TROUBLESHOOTING GUIDE If your FM25A does ...

Page 22: ...nited States this is how the FCC regards your transmitter kit Licensed FM broadcast stations and their listeners have ALL the rights Your use of a device such as the FM25A kit MAY have some limited privileges in lo cally unused band space but your non licensed use of the FM25A has abso lutely NO rights at all over the rights of licensed broadcast operators and the rights of their listeners to inte...

Page 23: ...d device to research and fully avoid any and all interference to licensed FM broadcast transmission and reception This instruction manual gives you practical advice on how to do a good job of finding a clear frequency if one is available 3 For some frequency bands the FCC sets 100 milliwatts 0 1 watt as the maximum permitted power output for unlicensed home built transmitting devices and that the ...

Page 24: ...his emission limit have your device checked by a technician with accurate measuring equipment Remember that the field strength of a signal is determined as much by the antenna as by the RF output of the transmitter itself APPENDIX B UNDERSTANDING LEGAL FIELD STRENGTH The new FCC Part 15 Rules specify a maximum Field Strength of your trans mitted signal Since it is unlikely that you have the equipm...

Page 25: ... over wider areas than you might have imagined For other kinds of radio services the FCC restricts such factors as transmitter power or antenna height which cannot really limit the possible range of a transmission under good conditions By restricting the maximum field strength at a specific distance from your antenna the FCC clearly plans for your signal to die out at a specific distance from your...

Page 26: ...d in the ARRL Radio Ama teur s Handbook can detect signals down to about 100 microvolts To measure RF field strength below such a level professional or laboratory equipment and sensitive receivers are required A sensitive receiver responds to a signal of 1 or even 5 microvolts delivered to the receiver input by antenna If the antenna is not good the receiver cannot respond to the presence of fract...

Page 27: ... identify your transmissions Only the FCC has the authority to issue such callsigns Use some other way to identify your transmitting activity such as This is Stereo 90 5 Seabreeze School Student Music Radio and so forth 9 Identify the location and purpose of your transmissions from time to time This is common courtesy toward other persons who may hear your signal The FCC is toughest about clandest...

Page 28: ... explore many frequency bands using many communica tions modes with no need for a formal license of any kind A thorough study of Part 15 of the FCC Rules which is completely beyond the purpose of this kit manual will show you many legal uses of radio transmitting devices which do not require licensing either amateur or commercial To provide more personal and club radio learning opportunities and t...

Page 29: ...ch be assured that the 1K ohm resistors are actually the missing 10 K parts Hum m m I guess the red band really does look orange Ramsey Electronics project kits are packed with pride in the USA If you believe we packed an incorrect part or omitted a part clearly indicated in your assembly manual as supplied with the basic kit by Ramsey please write or call us with information on the part you need ...

Page 30: ... RS64 2078 Holder for PC Board Parts Ramsey RTS13 RS64 2094 Desoldering Braid Ramsey RTS08 RS 2090 SYNTHESIZED STEREO TRANSMITTER KIT Quick Reference Page Guide Introduction 4 Circuit Description 5 Parts Layout Diagram 7 FM25A Parts List 8 Assembly Procedure 10 Schematic Diagram 16 Troubleshooting 23 FCC Rules and Information 24 Understanding Field Strength 26 Summary 28 Warranty 31 TOTAL SOLDER P...

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