DPT - Crystal Controlled ( Dual Power ) FM Transmitter
The Original
Circuits Below Were Built and Sold - In The Thousands To Law
Enforcement. Their Original Research and Development Cost , By Today's
Standards, Would Total - Well Over A Million Dollars.
 |
| The DPT Transmitter is a dual powered Voice Transmitter that came about from quite a few request 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, I.E. - 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.