Explanation for a circuit?

FYI: THIS CIRCUIT IS ILLEGAL TO JAM RADIO STATIONS BY FCC REGULATIONS AND IS A FEDERAL CRIME !!! IT WILL COST YOU $25,000 AND SEISURE OF ALL EQUIPMENT.

http://www.fcc.gov/encyclopedia/jammer-enforcement

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C4 is a large "hold-up" or bypass cap to provide energy when the circuit is operating; like a small battery.

http://en.wikipedia.org/wiki/Bypass_capacitor

R1 and R2 is a voltage divider that sets the base of the transisitor at a specific bias point, which is:

9V * (3,900 / (3,900 + 15,000) = 9V * 0.2063 = 1.8571 V

http://en.wikipedia.org/wiki/Voltage_divider

C3 is a stabiliting cap for the divider network with a time constant for charging at

R1 * C3 = 15,000 ohms * 0.01E-6 F = 150 microseconds (μs)

http://en.wikipedia.org/wiki/RC_time_constant

Q1 is an NPN which is biased on and normally off; meaning than the current will not flow from collector to emitter when not biased. Most circuits use NPN since it is positive logic for current flow thru the transistor.

http://en.wikipedia.org/wiki/Bipolar_transistor

C1 and L1 form the resonant tank circuit for a parallel L-C circuit. It will resonate at the frequency of the FM band when tuned to a specific frequency (87.5–108.0 MHz band). C1 is a variable capacitor or vari-cap that is screwed to a specific capacitance to set the resonance frequency.

http://en.wikipedia.org/wiki/Variable_capacitor

http://en.wikipedia.org/wiki/LC_circuit

http://en.wikipedia.org/wiki/Fm_radio#Broadcast_ba...

C2 is a snubber cap to release the energy of the inductor to prevent destroying the transistor:

http://en.wikipedia.org/wiki/Snubber

http://en.wikipedia.org/wiki/Snubber_capacitor#Snu...

R3 is to limit the L-C current and protect the transistor by limiting current flow thru it when it is biased on; which is always. If the resistance of L is r (very small), then the current thru the transistor is 9V / 220 = 40.9 mA with a power thru the transistor of it's drop times the current so :

0.24V * 0.0409A = 0.0098 W or about 10 mW

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This circuit has a problem with the antenna that is too short !!

Wavelength (λ) = speed of light (c) divided by the frequency (f)

λ = c / f

using a center frequency of ((108 MHz - 88 MHz) / 2) + 88 MHz = 98 MHz

λ = (299,792,458 m/s) / 98 MHz

λ = 3.0591 m

since the maxium voltage for the waveform occurs at 90 degrees or π/4, then it is maximum at λ/4

λ / 4 = 3.0591 m / 4 = 0.7648 m

λ / 4 = 76.48 cm

using 95% from parasitic impedances:

λ / 4 * 0.95 = 72.65 cm {this is the length of the wire that you need to attach to the coil !! }

a 30 cm wire will give you a different center frequency that is close to 1 GHz !