1 Watt PLL FM Broadcast Transmitter


1 Watt PLL FM Broadcast Transmitter


This is a 1 Watt PLL FM broadcast transmitter. The RF output varies from 500mW to about 1.2W depending on the frequency selected and RF output transistor used. Motorola 2N4427 always seems to work well. Transmitter uses CMOS PLL VCO that prevents the frequency drifts. The frequency is selected via DIP switches. The transmitter is supplied by 12V DC and can also be powered from the battery.

1 Watt PLL FM Broadcast Transmitter

This is a rather crude PCB layout i did using MS Paint. Not the best but it should work

This shows the test point for the PLL lock voltage. Ideally, it should be set for 3Volts (in the middle) using the oscillator coil. If the voltage doesn't change, oscillator may be at the end of its range in which case then c3 should be either increased slightly for a lower frequency and decreased for higher frequency. Try 22pf plus/minus 10pf

Component Values for VHF PLL


R1 - 10K
R2 - 10K
R3 - 10K
R4 - 10K
R5 - 10K
R6 - 100R
R7 - 1K
R8 - 10K
R9 - 470R
R10 - 10K
R11 - 470R
R12 - 100R
R13 - 470R
R14 - 10K
R15 - 10R
R16 - 47R
R17 - 10R
R18 - 100K
R19 - 1K
R20 - 10K
R21 - 10K
R22 - 1M
R23 - 100K
R24 - 100K
R25 - 100R

RP1 - 9 Pin 100K Commoned Resistor array
RP2 - 9 Pin 100K Commoned Resistor array


C1 - 1uF electrolytic
C2 - 27pF ceramic
C3 - 22pF ceramic (tuning cap- change to extend tuning range)
C4 - 27pF ceramic
C5 - 100pF ceramic (101)
C6 - 100pF ceramic (101)
C7 - 100pF ceramic (101)
C8 - 1000uF electrolytic
C9 - 100nF ceramic (104)
C10 - 100nF ceramic (104)
C11 - 100pF ceramic (101)
C12 - 4.7pF ceramic
C13 - 100nF ceramic (104)
C14 - 100nF ceramic (104)
C15 - 100nF ceramic (104)
C16 - 100nF ceramic (104)
C17 - 100nF ceramic (104)
C18 - 39pF ceramic
C19 - 39pF ceramic
C20 - 39pF ceramic
C21 - 39pF ceramic
C22 - 1nF ceramic (102)
C23 - 10nF ceramic (103)
C24 - 47uF electrolytic
C25 - 1uF electrolytic
C26 - 10uF electrolytic
C27 - 100nF ceramic (104)
C28 - 100nF ceramic (104)
C29 - 100nF ceramic (104)
C30 - 100nF ceramic (104)
C31 - 100pF ceramic (101)
C32 - 100nF ceramic (104)
C33 - 47uF electrolytic
C34 - 100nF ceramic (104)

VC1 - 2..22pF green trimmer
VC2 - 5..60pF yellow trimmer
VC3 - 2..22pF green trimmer
VC4 - 2..22pF green trimmer


L1 - Toko tuning coil with screening can 5.5 turns 100-075
L2 - Toko S18 Yellow
L3 - Toko S18 Yellow
L4 - Toko S18 Green
L5 - Toko S18 Green
L6 - Toko S18 Orange
L7 - Toko S18 Orange
L8 - RF choke 10uH-100uH


VD1 - Variable capacitance diode
VD2 - Variable capacitance diode
VD3 - Variable capacitance diode
D1 - 1N4841
ZD1 -BZX 6.2V Zener Diode

Q1 - BSX20
Q2 - BSX20
Q3 - BSX20 (or ztx313 on older boards)
Q4 - BSX20 (or ztx313 on older boards)
Q5 - 2N4427 with clip on heatsink (Motorola will give more power)

74HC4024 - Binary Counter
74HC4060 - Binary counter with oscillator
74HC4046 - Phase locked loop IC
74HC4059 - Divide by N counter


6.4 Mhz Quartz Crystal
DIP1 - 8 Way DIL DIP Switch
DIP2 - 8 Way DIL DIP Switch

Update: I finally got round to redrawing this in EAGLE. You can download the EAGLE PCB files below.
Here are some 3D renders of the Gerber files.

1 Watt PLL FM Broadcast Transmitter

1 Watt PLL FM Broadcast Transmitter

1 Watt PLL FM Broadcast Transmitter

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