SYNTHESIZED FM STEREO TRANSMITTER 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.
PARTIAL LIST OF AVAILABLE KITS RAMSEY TRANSMITTER KITS • FM25, MP3FM FM Stereo Transmitters • AM1 AM Transmitter • TV6 Television Transmitter • FM100 Professional FM Stereo Transmitter RAMSEY RECEIVER KITS • FR1 FM Broadcast Receiver • AR1 Aircraft Band Receiver • SR2 Shortwave Receiver • AA7 Active Antenna • SC1 Shortwave Converter RAMSEY HOBBY KITS • SG7 Personal Speed Radar • SS70A Speech Scrambler • MX5, MX10 Mixers • MD3 Microwave Motion Detector • PH10 Peak hold Meter • STC1 Stereo Transmitter Compani
Ramsey Publication No. MFM25A Price $5.00 KIT ASSEMBLY AND INSTRUCTION MANUAL FOR SYNTHESIZED FM STEREO TRANSMITTER KIT TABLE OF CONTENTS Introduction ...................................... 4 Circuit Description ............................ 5 Parts Layout Diagram ...................... 7 FM25A Parts List.............................. 8 Assembly Procedure ........................ 10 Schematic Diagram .......................... 16 Case and Knob Assembly ................ 18 Choosing an Operating Frequency ..
INTRODUCTION The Ramsey FM25A is a true SYNTHESIZED STEREO FM broadcast transmitter, which any person may build and use in accordance with the rules of your nation’s telecommunications authority. For U.S. residents, that authority is the Federal Communications Commission (FCC). The FM25A’s low-power broadcasting capability and other practical uses can be fun and interesting for people of all ages, but the FM25A is not a toy.
CIRCUIT DESCRIPTION We will begin by talking about the power supply of your new FM25A. While a DC power source is provided with the FM25A, the DC isn’t ‘proper’ enough to provide us with the low-noise, stable supply that we would like for good audio quality. Voltage regulator VR3 provides us with a means to take the raw DC output from the wall transformer and ‘smooth’ it out, keeping it at a constant 12 volts. Filter capacitor C5 reduces ripple noise from the DC wall transformer.
may think that all this would take a long time but in fact the whole process from the time you press the program switch until the data is completely sent is less than 1/100th of a second! U1 is a phase locked loop (PLL) synthesizer IC. It takes the 6 MHz crystal frequency and divides it by 60 to obtain a stable reference frequency of 100KHz.
FM25A PARTS LAYOUT DIAGRAM FM25A • 7
PARTS SUPPLIED WITH FM25A TRANSMITTER KIT Capacitors 8 .001 µF disc capacitors (marked .001, 102 or 1nF) [C10,C12,C13,C26, C27,C28,C29,C31] 7 .01 µF disc capacitors (marked .01 or 103 or 10 nF) [C7,C8,C15,C23, C24,C42,C43] 2 .1 µF disc capacitor (marked .1 or 104 or 100 nF) [C9,C16] 2 .022 uF ceramic capacitors (marked .
Hardware, Misc. 1 6 MHz crystal (thin shiny rectangle marked 6.00) [Y1] 1 38 KHz crystal (small silver cylinder with two small leads), taped to paper. [Y2] 1 78L05 +5 volt voltage regulator [VR1] 1 78L02 +2.
RAMSEY "LEARN-AS-YOU-BUILD" ASSEMBLY STRATEGY As you can see in examining the circuit board and components, there is a bit more to this kit than just soldering a few parts. So that you don't spend extra time "troubleshooting" instead of getting on the air, we strongly recommend that you follow the assembly strategy and step-by-step procedures we provide. Our strategy in installing parts on our PC board is to install the larger and more obvious parts such as the connectors and controls.
1. Install S1, the DPDT horizontal push-button switch. It fits correctly only one way. Ensure that the white plastic switch extends out over the edge of the printed circuit board. Solder all six pins. 2. Install S2, the small black mini push-button switch. Solder all 4 or 2 pins depending on the switch provided. This switch snaps into place and sits flush with the top of the board. 3. Install J2, the Right Channel input jack. Solder all 4 points of the jack securely. 4.
Audio Input Circuits We encourage you to refer to the schematic diagram and learn the functions of the following parts. If you wish, insert the parts groupings as one operation, then solder and nip all connections. Most of the resistors will be installed in a stand up fashion. That is, one lead will go straight into the board while the other is bent around to go back down into the other hole. The straight lead goes into the hole with the circle around it. 1a.
Power Supply 1b. Install C5, the large 470 - 1000 µF electrolytic capacitor. Be sure to position for correct polarity. 2b. Install VR3, the 7812 12 volt regulator. Make sure the metal tab is oriented as shown in the parts layout. The text side of the component should be facing S1. 3b. Install VR1, the 78L05 5 volt regulator. Make sure the flat side of the component is facing the same direction as shown. 4b. Install C7, a .01µF ceramic capacitor (marked .01, 103, or 10n). 5b.
and insert back into the can. Make sure L1 is squarely against the top of the PC board before soldering. Solid installation of L1 is essential to the frequency stability of your transmitter. 16c. Install R8, 47K ohms (yellow-violet-orange). 17c. Install C16, .1 µF disc capacitor (marked 104 or .1). 18c. Install VR2, the 78L02 2.6 volt regulator (TO-92 transistor style package). Make sure the flat side is oriented the same way as shown in the parts layout diagram. 19c.
8d. Install Q2, the other transistor marked C2498 (or 2570). Again watch the placement of the flat side and mount as flush as possible. 9d. Install R18, 10K ohms (brown-black-orange). 10d. Install R14, 220 ohms (red-red-brown). 11d. Install C23, .01 µF (marked .01 or 103 or 10 nF). RF Lowpass Filter 1e. Install C35, a 47pF ceramic capacitor (marked 47 or 47K). 2e. Install C27, a .001µF ceramic capacitor (marked .001, or 102).
16f. Install R31, a 1K ohm resistor (brown-black-red). Notice this resistor is a laydown component. 17f. Install C8, .01 µF disc capacitor (marked 103 or .01 or 10 nF). 18f. Install R1, 10K ohms (brown-black-orange). 19f. Install Q1, the transistor marked 2N3904. The flat side must be placed as shown on the PC board, facing C6. Mount it as close to the board as possible without forcing it. 20f. Install C6, 10 µF electrolytic capacitor. Check polarity! 21f.
CHOOSING AN OPERATING FREQUENCY (A) It really is NOT sufficient to just "check" the FM band for an empty frequency, using the FM portable radio closest at hand. It is your responsibility to carefully research what FM stations can be listened to with a good system within the transmitting range of your FM25A. This is especially important in the low end of the FM broadcast band (88-92 MHz), where there are numerous medium power National Public Radio stations.
After setting your DIP switches, recheck your ‘math’, depress the Program button and listen on a nearby FM radio for the carrier frequency. No audio input is needed to make this first adjustment, you can simply listen for a "quieting" in the normal background noise "hiss." Remember that if you have adjusted the FM25A outside of 88 MHz to 108 MHz range it will default to 88.1 MHz. This means that if you can’t hear anything on the radio near the frequency you are trying to transmit at, go to 88.
USING THE FM25A WITHIN THE HOME A most practical use for the FM25A would be to connect it to the main stereo system within a large home so that whatever is playing on the main system can also be tuned-in on portable FM radios in other rooms, the garage or in the yard. This connection consists of using shielded audio cables to connect the auxiliary "line audio" output of your cassette deck, CD player or other stereo device to the audio inputs of the FM25A.
RAMSEY’S HAS MIXER (MX) KITS! You can greatly add to the versatility and professionalism of your transmitting station by adding one of our audio mixers and processor. Mixers allow you to smoothly ‘blend’ from one audio source to another just like the commercial stations do. Our STC1, Stereo Transmitter Companion provides full audio processing in one easy package. The STC1 allows you to ‘sweeten’ the audio for more impact and punch.
Ham radio books and magazines are filled with antenna principles and ideas which can be adapted to your application. Also, you may wish to look at Radio Shack book No. 62-1083 on antennas. Our new TM-100 Tru-match FM antenna is an ideal mate to your transmitter. It features proper impedance matching for optimum power transfer and range. See our catalog for details.
APPENDIX A: FCC RULES AND INFORMATION The Rules of the FCC (Federal Communications Commission)and your kit built FM Stereo Transmitter. An interim explanation of applicable FCC regulations supplied as a personal assistance to FM25A builders, by Dan F. Onley (K4ZRA) It is the policy of Ramsey Electronics, Inc., that knowing and observing the lawful use of all kits is a first responsibility of our kit user/builders.
Here are the primary "dos and don'ts" picked from the current FCC Rules, as of May, 1990. This is only a brief look at the rules and should not be construed to be the absolute complete legal interpretation! It is up to you to operate within the proper FCC rules and Ramsey Electronics, Inc. cannot be held responsible for any violation thereof. 1. In the past, no "two-way communications" use of the 88-108 MHz FM broadcast band was permitted.This prohibition does not appear in the current edition of Part 15.
kit operates well within this limit. In fact, its signal should sound no "wider" than any other FM station when listening on an ordinary FM radio. • b. FCC Rule 15.215(a) says: "Unless otherwise stated, there are no restrictions as to the types of operations permitted under these sections." This general provision appears to leave you free to use your FM stereo transmitter in a manner similar to operations of an FM broadcasting station, or to use it for any other non-interfering, practical application.
chart to show the maximum permitted performance of a non-licensed FM band transmitter. The theoretical figures assume a simple 1 meter receiving antenna in all cases and do not take into consideration that reception can be greatly enDISTANCE FROM TRANSMITTER ANTENNA METERS FEET FIELD TOTAL AREA 3 10 250 314 FT 6 20 125 1256 FT 12 39 63 4800 FT 24 78 31 19113 FT 48 157 15 1.8 ACRES 96 315 7.5 7.2 ACRES 192 630 3.8 28.6 ACRES 384 1.9 11.4 ACRES 768 1260 2520 .
There are three reasons to translate our look at "field strength" into "acres". 1. The first one is easy: the numbers would get too cumbersome if we discussed your possible signal coverage in terms of square feet or square meters. 2. It's very easy to see that your signal can easily and legally serve a school campus or wilderness campground. 3.
to accomplish any objective which the FCC sees to be in the public interest and not interfering with other authorized uses of the radio spectrum. Lawful use suggestions 1. Build and adjust this kit strictly according to the published instructions. 2. Use the whip antenna supplied with the Ramsey case set, CFM. 3. Do not modify your kit in any way. 4.
NOTICE: The radio-frequency "intentional radiator" device which may be constructed from kit parts supplied by us is intended and designed by Ramsey Electronics, Inc. to conform to applicable provisions of Part 15 of FCC Rules. The individual kit-builder and all users of this device assume responsibility for lawful uses conforming to FCC Part 15 Rules. Operation is subject to the following two conditions: 1. This device may not cause harmful interference, and 2.
The Ramsey Kit Warranty Please read carefully BEFORE calling or writing in about your kit. Most problems can be solved without contacting the factory. Notice that this is not a "fine print" warranty. We want you to understand your rights and ours too! All Ramsey kits will work if assembled properly. The very fact that your kit includes this new manual is your assurance that a team of knowledgeable people have field-tested several "copies" of this kit straight from the Ramsey Inventory.
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.............
