FM STEREO TRANSMITTER Ramsey Electronics Model No. FM10A Own and operate your own FM Stereo broadcast station. Definitely not a toy, the FM-10A has an exceptional transmission range... and the audio quality puts your favorite radio station to shame. See why this is one of our most popular kits! • 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 • FM25B FM Stereo Transmitter • AM1, AM25 AM Transmitters • TV6 Television Transmitter • FM100B 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, MX-10 Mixers • MD3 Microwave Motion Detector • PH14, 15, 16 Peak hold Meter Kits • TFM3 Tri-Field M
Ramsey Publication No. MFM10A Manual Price Only: $5.00 KIT ASSEMBLY AND INSTRUCTION MANUAL FOR FM10A FM STEREO TRANSMITTER TABLE OF CONTENTS Introduction to the FM10A........................................ 4 FM10A Circuit Description ....................................... 5 Schematic Diagram.................................................. 5 Parts List .................................................................. 6 Parts Layout Diagram ..............................................
INTRODUCTION The Ramsey FM10A is a true 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 FM10A's low-power broadcasting capability and other practical uses can be fun and interesting for people of all ages, but the FM10A is definitely not a toy.
CIRCUIT DESCRIPTION A quick glance at the Schematic Diagram shows that the custom FM stereo transmitter IC (U1) is at the heart of the FM10A. The control of U1 is determined by its surrounding circuitry. Potentiometers R1 and R4 allow for adjustment of input level. Resistors R3 and R6 set the pre-emphasis characteristics (75uS for USA and 50uS for Europe). R7 permits adjustment of stereo balance. L1 and C16 form an adjustable resonant circuit to set the carrier operating frequency.
PARTS LIST CAPACITORS 4 10 pf disc capacitor (marked 10 or 10K) (C7,8,14,15) 1 18 pf disc capacitor (marked 18) (C16, see note below) 1 22 pf disc capacitor (marked 22) (C16, see note below) 1 27 pf disc capacitor (marked 27) (C16, see note below) NOTE: Selecting 18, 22 or 27 pf for C16, establishes the FM-band frequency adjustment range. See “Choosing an Operating Frequency.” 1 220 pf disc capacitor (marked 220 or 221) (C9) 8 .001 µF disc capacitor (marked .
REQUIRED, NOT SUPPLIED: 9-volt alkaline or heavy-duty battery Shielded stereo audio cables Line-level output audio source (such as a tape deck or CD player) External antenna, small gauge coax and RCA plug, OR PC board mounted telescoping whip antenna (included with the Ramsey CFM case and knob set.
ASSEMBLY INSTRUCTIONS Building your FM10A Stereo Transmitter The following FM10A step-by-step assembly and adjustment directions are written with newcomers in mind. While many Ramsey kits are purchased by experienced hobbyists and ham radio operators, our instructions presume that this stereo transmitter could be your first ever kit project. Ramsey Electronics Kit instruction manuals are designed around our "Learn as You Build" philosophy.
• • SOLDER ALL wires or pins of the part, whether the two wires of a resistor or the 18 pins of an IC socket. Nip or "trim" all excess wires extending beyond each solder connection, taking care that wire trimmings do not become lodged in PC board solder connections. Enough said. . . Let's get building! 1. Install S1, the DPDT 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.
Wiring the audio input circuits We encourage you to peek at the schematic diagram and learn the functions of the following parts. However, the sequence of installation is in the order of convenience and speed. If you wish, insert the parts groupings as one operation, then solder and nip all connections. 8. Install R1, one of the small yellow trimmer potentiometers marked "102". Don't confuse it with R7 which is marked "104". 9. Install R4, the other yellow trimmer marked "102".
17. Install glass bead diode D1. 18. Install glass bead diode D2. 19. Install glass bead diode D3. 20. Install R7, the small yellow trimmer potentiometer marked "104". 21. Install C19, the 470 µF electrolytic. Be sure to position for correct polarity. 22. Install C11, 4.7 to 10 µF electrolytic. Observe polarity. 23. Install R11, 4.7K [yellow-violet-red]. 24. Install R12, 150K [brown-green-yellow]. 25. Install C9, 220 pf [marked 220 or 221]. 26. Install C10, .001 µF [marked .
35. Install R10, 10K ohms [brown-black-orange]. The following two capacitors have the identical functions of coupling the RF output from the collector of Q1 to the RF output jack (J3) and also the mounting point provided if you wish to use an on-board whip antenna. 36. Install C13, .001 µF (marked .001 or 102 or 1 nf). 37. Install C21, .001 µF (marked .001 or 102 or 1 nf). 38. The 3 holes for Q1, the 2SC2498 or 2SC2570A RF power amplifier transistor, should now be quite clear.
FM10A frequency range selection Capacitor C16 sets the frequency range of the FM10A. Values for C16 are as follows: Desired Transmitter Frequency Range C16 Value Lower end of FM band.......... (88-94 MHz) .... 27 pf Middle portion of FM band ... (91-100 MHz) ... 22 pf High end of FM band ........... (95-108 MHz) ...
ADJUSTING YOUR FM10A TRANSMITTER Keep all tests very brief until you have carefully chosen an open operating frequency in the FM broadcast band. 1. Transmitting Frequency: After finding a suitable "open" frequency in the 88-108 MHz FM band, adjust L1 with the plastic alignment screwdriver until you hear the carrier frequency on a nearby FM radio. No audio input is needed to make this first adjustment, you can simply listen for a "quieting" in the normal background noise "hiss." 2.
USING THE FM10A WITHIN THE HOME A most practical use for the FM10A 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 out 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 FM10A.
to the negative battery wire. The resistor is omitted if you are using a 1.5 volt battery for prolonged short-range operation. EXPERIMENTAL "BROADCASTING" PROJECTS To use the FM10A successfully as a "broadcasting" service to interested listeners in a school or immediate neighborhood, most of your effort will be concentrated on smoothly "managing" or mixing the audio signals fed into the transmitter input. Operation of the transmitter itself consists simply of the following: 1.
Although many sources exist for audio mixers, the Radio Shack No. 321105 is the least expensive commercial device currently available. Bear in mind that specifications and model numbers for such accessory equipment can change from year to year. Also, some home-entertainment audio equipment includes simple mixing capabilities which will permit you to fade and "cue" music and microphone inputs.
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. ANTENNA ALTERNATIVES If your situation involves a single large building or multi-level home where reception from the FM10A antenna tends to be uneven because of walls and other VHF path obstacles, you might set up the FM10A's output in a "carriercurrent" configuration. If you know how to do correctly, then do so - safely.
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 FM10A 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.
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. Previous editions of Part 15 discussed "wireless microphones" (such as Ramsey FM-1, FM-4, etc.), while the June 23, 1989, revision eliminates this discussion in favor of more detail regarding computer and TV peripherals and other modern electronic conveniences.
space for several different FM stations, this is a "generous" limitation designed to accommodate cruder FM devices. Properly built and adjusted, the FM10A 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. • c. FCC Rule 15.215(a) says: "Unless otherwise stated, there are no restrictions as to the types of operations permitted under these sections.
APPENDIX B: UNDERSTANDING LEGAL "FIELD STRENGTH" A "microvolt" is one-millionth of one volt and designated "µV" in the following explanations. The new FCC Part 15 Rules specify a maximum "Field Strength" of your transmitted signal.
DISTANCE FROM TRANSMITTER ANTENNA METERS FEET FIELD STRENGTH (µV) TOTAL RECEPTION 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 1260 1.9 11.4 ACRES 768 2520 .95 458 ACRES 1536 5036 .5 1830 ACRES broadcast on a school campus, campground or local neighborhood, as long as you do not cause interference to broadcast reception.
In fact, the most significant distance in the above chart is the 1.9 µV signal strength permissible at 1260 feet (about 1/4 mile), covering a circular area of about 114 acres. A quick glance at stereo FM receiver specifications shows typical sensitivity of 1.7 µV before considering high-gain antennas or preamplifiers.
4. Check your intended operating frequency very carefully, as clearly explained in this instruction manual, to ensure you will not cause interference to reception of licensed broadcasting. 5. If you receive ANY complaint about your transmissions interfering with broadcast reception, stop or change your operation IMMEDIATELY. 6. If you are contacted by the FCC regarding use of this device, cooperate fully and promptly. 7.
[1] This device may not cause harmful interference, and [2] this device must accept any interference received, including interference that may cause undesired operation. Final comment A well-informed person will see today's FCC Rules to be evolving and progressively less-restrictive.
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.
FM10A STEREO TRANSMITTER KIT Quick Reference Page Guide Introduction .......................................4 Circuit description .............................5 Schematic diagram ...........................5 Parts list ............................................6 Parts layout board .............................7 Assembly instructions .......................8 Adjusting your FM10A ......................14 Troubleshooting guide ......................18 Appendix A: FCC rules and info .......