FM Stereo TransmitterCharlie RogersFM Stereo Transmitter
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| Capacitors: | |||
| 4 | 10pf disc capacitor | ||
| 1 | 18pf disc capacitor | ||
| 1 | 22pf disc capacitor | ||
| 1 | 27pf disc capacitor | ||
| 1 | 220pf disc capacitor | ||
| 8 | .001 mF disc capacitor | ||
| 2 | .0047 mF disc capacitor | ||
| 3 | 4.7 to 10 mF electrolytic capacitor | ||
| 1 | 470 mF electrolytic capacitor | ||
| 1 | 1000 mF electrolytic capacitor | ||
| Resistors: | |||
| 2 | 270 ohm | ||
| 1 | 470 ohm | ||
| 1 | 4.7 ohm | ||
| 3 | 10K ohm | ||
| 2 | 15K ohm | ||
| 1 | 150K ohm | ||
| 1 | 100K yellow trimmer potentiometer | ||
| 2 | 1K yellow trimmer potentiometer | ||
| Semiconductors: | |||
| 3 | Glass bead diodes | ||
| 1 | 2SC2498 or 2SC2570A NPN VHF transistor | ||
| 1 | 18-pin DIP Custom FM Transmitter integrated circuit (U1) with matching socket | ||
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Hardware and Miscellaneous: |
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| 1 | 38KHz crystal | ||
| 1 | Shielded inductor coil | ||
| 1 | Ramsey FM10A Printed circuit board | ||
| 1 | Plastic alignment screwdriver | ||
| 1 | PC board mounted push-button switch | ||
| 3 | RCA-type PC-mount jacks | ||
| 1 | 2.5 mm phone jack | ||
| 1 | 9-volt battery hold-down clamp | ||
| 1 | 9-volt battery snap connector | ||
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Required, Not Supplied: |
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| | 9-volt alkaline or heavy-duty battery | ||
| | Shielded stereo audio cables | ||
| | Line-level output audio source (tape deck or CD player) | ||
| | External antenna, small gauge coax and RCA plug, OR PC board mounted telescoping whip antenna | ||
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Optional: |
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| | Ramsey FM10A case and knob set | ||
| | LED power on indicator and 1K resistor | ||
| | Audio switching-mixing accessories of your choice | ||
| Pictures:
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| Theory: | |||
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The FM10A is a true stereo FM broadcast transmitter. Its low-power broadcasting capability and other practical uses can be fun and interesting, but it is definitely not a toy. The Federal Communications Commission (FCC) is the U.S. telecommunications authority, and proper observance of the FCC regulations in using the FM10A will allow you to enjoy its capabilities in accordance with the law. A quick look at the schematic shows that the main controller of the FM10A is the custom FM stereo transmitter integrated circuit (U1), and its control is determined by its surrounding circuitry. The 1K potentiometers allow for adjusting the levels for the left and right audio inputs. The 15K ohm resistors set the pre-emphasis characteristics for the FM10A. Pre-emphasis is a technique used to increase the high frequency signal to noise ratio. In North America and Japan, 15K ohm resistors are used, whereas Europe, Russia and some other countries use the 10K ohm resistors. The 100K potentiometer is used to permit adjustment of stereo balance between the left and right audio inputs. The shielded inductor coil and the disc capacitor set in slot C16 form an adjustable resonant circuit to set the carrier operating frequency. The C16 capacitor slot determines the frequency range for the FM10A. The values for C16 are as follows: Desired Transmitter Frequency Range
C16 Value The three glass bead diodes regulate the voltage to U1 at 2.1 volts of direct current. The radio frequency output of the VHF transistor at Q1 feeds on both the on-board whip antenna and the RCA port at J3 for an external antenna. The typical uses for the FM10A include: |
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| | Extension of home stereo system without wires | ||
| | Listening aid for auditoriums and churches | ||
| | Student-operated school radio station | ||
| | College dorm favorite music broadcast service | ||
| | Short-range, two-channel experiments and demonstrations | ||
| Problems: | |||
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As with all soldering projects, there are possibilities of bridging soldering points, causing the board to malfunction. I have had problems with this in the past, and I have had to double-check myself several times to keep from creating bridges. Broadcasting at the dorms at Southeast Housing proved to be difficult, mainly because the walls are reinforced concrete and that disturbs the transmission. |
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