Spy FM Transmitter

  
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Build this circuit using a Digi-Key Electronics Barrel Crystal (CA-301), 15 Mhz for a standard output frequency of 150. 00 Mhz. If you want to customize the frequency, follow the directions below. I usually build this circuit to operate between 150 to 165 Mhz. The Crystals I use Are The Digi-Key Electronics Barrel Crystals CA-301 Type which cost a couple of bucks per crystal.
Spy FM Transmitter - schematic

This circuit uses a X5 Multiplier and then a X2 Multiplier In the Final. Example: If I use a 15 Mhz Barrel Crystal, the frequency at Q4s output is: Xtal X 5 Or: 75 Mhz into Q5. Q5 Multiplies 75 Mhz X 2 for an end frequency out of the final Q6 ( Desired Output Frequency ) of 150. 00 Mhz. Virtually any Fundamental Crystal between 14 and 17 Mhz will output a frequency of between 140 to 170 Mhz, if the crystal has a load capacitance of around 18 pf. If you wish to build this transmitter on A custom frequency simply use the X5 X2 formula below and order a custom cut crystal specifying an 18 pf CL. I would order the crystal at a Fundamental frequency of 15. 825 Mhz, tolerance of. 001% and a Crystal Load Capacitance of 18 pf. When I tune my transmitter, my output transmit frequency would be: 158. 250 Mhz. 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.



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