This is the schematic for an FM transmitter with 3 to 3.5 W output power that can be used between 90 and 110 MHz. Although the stability isn't so bad, a PLL can be used on this circuit. This is a circuit that I've build a few years ago for a friend, who used it in combination with the BLY88 amplifier to obtain 20 W output power. From the notes that I made at the original schematic, it worked fine with a SWR of 1 : 1.05 (quite normal at my place with my antenna).
Schematic
Parts
| Part | Total Qty. | Description | Substitutions |
| R1,R4,R14,R15 | 4 | 10K 1/4W Resistor |
|
| R2,R3 | 2 | 22K 1/4W Resistor |
|
| R5,R13 | 2 | 3.9K 1/4W Resistor |
|
| R6,R11 | 2 | 680 Ohm 1/4W Resistor |
|
| R7 | 1 | 150 Ohm 1/4W Resistor |
|
| R8,R12 | 2 | 100 Ohm 1/4W Resistor |
|
| R9 | 1 | 68 Ohm 1/4W Resistor |
|
| R10 | 1 | 6.8K 1/4W Resistor |
|
| C1 | 1 | 4.7pF Ceramic Disc Capacitor |
|
| C2,C3,C4,C5,C7,C11,C12 | 7 | 100nF Ceramic Disc Capacitor |
|
| C6,C9,C10 | 3 | 10nF Ceramic Disc Capacitor |
|
| C8,C14 | 2 | 60pF Trimmer Capacitor |
|
| C13 | 1 | 82pF Ceramic Disc Capacitor |
|
| C15 | 1 | 27pF Ceramic Disc Capacitor |
|
| C16 | 1 | 22pF Ceramic Disc Capacitor |
|
| C17 | 1 | 10uF 25V Electrolytic Capacitor |
|
| C18 | 1 | 33pF Ceramic Disc Capacitor |
|
| C19 | 1 | 18pF Ceramic Disc Capacitor |
|
| C20 | 1 | 12pF Ceramic Disc Capacitor |
|
| C21,C22,C23,C24 | 4 | 40pF Trimmer Capacitor |
|
| C25 | 1 | 5pF Ceramic Disc Capacitor |
|
| L1 | 1 | 5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm |
|
| L2,L3,L5,L7,L9 | 5 | 6-hole Ferroxcube Wide band HF Choke (5 WDG) |
|
| L4,L6,L8 | 3 | 1.5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm |
|
| L10 | 1 | 8 WDG, Dia 5 mm, 1 mm CuAg, Space 1 mm |
|
| D1 | 1 | BB405 | BB102 or equal (most varicaps with C = 2-20 pF [approx.] will do) |
| Q1 | 1 | 2N3866 |
|
| Q2,Q4 | 2 | 2N2219A |
|
| Q3 | 1 | BF115 |
|
| Q5 | 1 | 2N3553 |
|
| U1 | 1 | 7810 Regulator |
|
| MIC | 1 | Electret Microphone |
|
| MISC | 1 | PC Board, Wire For Antenna, Heatsinks |
|
Notes
- Email Rae XL Tkacik with questions, comments, etc.
- The circuit has been tested on a normal RF-testing breadboard (with one side copper). Make some connections between the two sides. Build the transmitter in a RF-proof casing, use good connectors and cable, make a shielding between the different stages, and be aware of all the other RF rules of building.
- Q1 and Q5 should be cooled with a heat sink. The case-pin of Q4 should be grounded.
- C24 is for the frequency adjustment. The other trimmers must be adjusted to maximum output power with minimum SWR and input current.
- Local laws in some states, provinces or countries may prohibit the operation of this transmitter. Check with the local authorities.
website:http://www.aaroncake.net
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