A problem with a circuit?

There are (2) keys for success in RF designs and both are inductive:

1. Make the coil as recommended since the coil you purchased probably is wound on a ferrite core that is not allowing the magnetic field to ratiate.

2. Make sure that you create an antenna *exactly* on the frequency that you are looking to use. Make sure that the antenna is cut to this length:

1/4 wavelength antenna (in meters - need to convert to inches)

one wavelength (λ) = speed of light (c = 299,792,458 meters per second) divided by the frequency (f)

e.g. 100.2 MHz FM station

λ = c / f

λ = (299,792,458 m/s) / 100.2E6 Hz

λ = 2.9919 meters for one wavelength

BUT you need 1/4 λ since the PEAK ENERGY is at the top of the wave at 1/4 λ.

so λ/4 = 2.9919 meters / 4 = 0.7480 meters

converting meters to inches

0.7480 meters = 748 mm * 1 inch/ 25.4 mm = 29.4482 inches or almost 30 inches.

{ in think that the instructions are supposed to be in inches not cm}

30cm = 0.30 m as 1/4 λ

λ = 4 * 0.30 m = 1.2 m

1.20 m = (299,792,458 m/s) / f

f = 249,827,048.3 Hz

f = 249.8270483 MHz {not even close !!! }

Using the formula

f = 1/(2π√(LC))

I get f = 123 Mhz which is above the FM band

I suggest you get a variable capacitor, wind the inductor on a pen. You must keep lead length short especially around L1, C1, C2 and Q1 otherwise this circuit won't work. I suggest you put a second capacitor of 0.01 μF in parallel with the electrolytic capacitor C4.

Breadboard is not suitable to build such high frequency FM jammer, because breadboard has too high

random capacitance and inductance between socket pins. Redo this circuit with soldering them directly.

This circuit shall not work well as a jammer without an antenna. And its range is not more than 20 feet.

How do you know .33 uH is correct. Make one like it says. You also need a variable cap. of 6 to 35 pF.