A problem with a circuit?

maximus

Have been trying to assemble the circuit shown here:

www.circuitstoday.com/fm-radio-jammer

On a breadboard before starting of on a pcb but its not working. Any idea why?

I havent wound a wire to make the inductor but have bought one (0.33uH readymade inductor) instead.

I am using a 5pF capacitor instead of 6pF, could that be causing the problem?

Have bought a 6pF one but haven't tried it yet. Is it necessary or should 5pF not be a problem?

Also if I connect a 1pF and 5pF in parallel, will it work as a substitute for the 6pF capacitor?

Would really appreciate the help.

pete-evans_60a6372748af5

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 !!! }

jordan-price_60a63728084bb

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.

chelsea-butler_60a63728c0e8e

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.

rob-king_60a637298572d

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