Home Projects RF circuits 3W FM Transmitter

 

 

3W FM Transmitter

source: http://www.aaroncake.net/

By Rae XL Tkacik

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

 

This is the schematic of the 3W FM Transmitter

 

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:

1. Email Rae XL Tkacik with questions, comments, etc.

2. 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.

3. Q1 and Q5 should be cooled with a heat sink. The case-pin of Q4 should be grounded.

4. C24 is for the frequency adjustment. The other trimmers must be adjusted to maximum output power with minimum SWR and input current.

5. Local laws in some states, provinces or countries may prohibit the operation of this transmitter. Check with the local authorities.

 

 
 

 

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