Electronic Circuits, Diagrams and Schematics

Dual Power FM VHF Xtal Voice Transmitter

The DPT ( Dual Power Radio Frequency FM Transmitter Circuit is a dual powered Voice Transmitter that came about from quite a few requests for a transmitter that would function both at power when long range was needed and with a "switch that could be thrown" for a smaller battery consumption when longer battery life was required. It operates in the low power range of 100 MW and at the high power range of 250 MW. Frequency of operation is in the upper to high VHF range. 

Dual Power Transmitter
© 2011 By John S. Wilson Jr.
john@bugplan.com

Parts List: Circuit # DPT -  Dual Power - 100/250 M.W.
Vhf Crystal Controlled - "Voice" Transmitter

Resistors: 1/4 Watt

R1 = 10K
R2 = 1 MEG
R3 = 4.7K
R4 = 100 Ohm
R5 = 10K
R6 = 220K
R7 = 10 Ohm
R8 = 5.6K
R9 = 1K
R10 = 1K Note: This resistor controls the deviation. It can be replaced with an adjustable pot between 500 ohms to 2K.
R11 = 10K
R12 = 10K
R13 = 10 Ohm
R14 = 100 Ohm
R15 = 4.7K
R16 = 4.7K
R17 = 10 Ohm
R18 = 4.7K
R19 = 2.2K
R20 = 100 Ohm
R21 = 10 Ohm

Capacitors: - Disc Or Electrolytic ( Electrolytic Shown with +/- )  All Low Voltage
C1 = .1
C2 = .001
C3 = .1
C4 = .01
C5 = 6.8 MFD
C6 = .1
C7 = .001
C8 = .01
C9 = 22 pf
C10 = 9 to 50 pf trimmer ( Adjustable ) capacitor
C11 = 5 pf
C12 = .001
C13 = .001
C14 = 9 to 50 pf trimmer ( Adjustable ) capacitor
C15 = 100 pf
C16 = .001
C17 = .1
C18 = 33 pf
C19 = 5 pf
C20 = 9 to 50 pf trimmer ( Adjustable ) capacitor

Transistors:
Q1 and Q2 = PN3904 - Dig-Key Electronics
Q3 and Q4 = PN918 - Digi-Key Electronics
Q5 =  2N2219A - Digi-Key Electronics                          

                                                          
Antenna
18 " Of small Diameter Flex wire

ON/OFF Switch:
Any, On / Off Switch Will Do - connecting the + side of the 6 volt battery to the circuit

BATTERY:
6 Volts D.C. ( FlatPack - Duracell # 7K67 ) The Negative Side Of The Battery Connects To The
 On/Off Switch to ground

M1:
Electret Mic. Element. Any small electret element will do. Digi-Key Electronics

L1:
15 Turns of # 26 Magnet Wire Wound tight on a Dig-Key Electronics Part Number 3368K-ND Fiber Washer

L2:
7 Turns of # 26 Magnet Wire Wound tight on a Dig-Key Electronics Part Number 3368K-ND Fiber Washer
 

L3: 6 Turns of # 22 Magnet Wire, Air Wound - using the smooth end of a 1/8" drill bit

L4: 3 Turns of # 22 Magnet Wire, Air Wound - using the smooth end of a 1/8" drill bit

XT1: ( CRYSTAL ) This circuit uses a 5th overtone crystal. Example: If I used a crystal with a cut of 79.25 Mhz - My end frequency ( Transmit ) would be 158.5 Mhz.

The circuit incorporates a X2 multiplier. Order your crystals - for a custom frequency at: 1/2 of your desired transmit frequency - SPECS: series resonance / 5th Overtone / .001% Tolerance / and then specify you choice of crystal design, ie - various sizes.

Order your crystal at 1/2 of the frequency of your desired transmit frequency! This circuit is fully functional from 150 to 170 Mhz.

Switch S2: Any small on/off type switch will do.

When the switch is open, the transmitter has an output power ( R.F. Transmit ) of 100 M.W.. When the switch is closed, the unit transmits an output power of 250 M.W.

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