This is a simple, but efficient broadband radio jammer. Most
jammers operates on a certain frequency, but this jammer is able to transmit broadband RF noise from medium wave band to FM broadcast band (VHF).

Step 1: Build the Driver Circuit.

You see, this is the well-known 2n3055 flyback driver so I will not go deeper into particulars.

Just few important things: wind the primary and the feedback coil in the same direction.

It is recommended to use a fast diode to protect the transistor from voltage spikes.

Use a large heatsink. My driver is a prototype and there is a small heatsink, the transistor gets hot in a few seconds.

I do not solder the flyback primary and secondary to the driver circuit, I use screws to fix them in order to mount different flybacks later.

I used two 120 ohm resistor in series and two 51 ohm resistors in parallel because only these types were in the shop.

You will need an old flyback transformer from black and white TV.

Step 2: Prepare the Flyback

Remove the original flyback primary coil

Make a small paper cylinder from hard paper and glue the primary and the secondary coil on it. Then place back the secondary and the new primary and feedback. When you assemble the flyback, don’t forget to place those thin plastic plates between the ferrite cores. They decrease the ultrasonic vibration.

The secondary coil you see in the picture above is a homemade,
thin, disc shaped secondary coil. It contains more turns than the original coil, and gives higher voltage.

The coil thickness is 1 mm with 0.1 mm (38 awg) magnet wire. It avoids internal arc between the windings. The coil is impregnated with paraffin wax.

My flyback works with a 20W power supply and gives 8-9 mm sparks. (It can be extended during operation to 20mm) If you want to pump more watts into the flyback, a homemade thin secondary is recommended, because high secondary voltage can easily destroy the original coil. The coil must not be thicker than 1 mm!

Use epoxy instead of parrafin wax! Paraffin melts easily. You can connect two or three coils in series to give higher voltage.

You can find a lot of instructions about homemade flyback secondary coils.

Step 3: Connect the Flyback With the Driver and Attach the Spark Gap and the Antenna.

Spark gap is 2-3 mm. Antenna is a 2 m long wire. The antenna
causes voltage drop that’s why the 8 mm spark length decrease to 2-3 mm. The range of the jammer is 10-15 m.

Using 6-8 m antenna will extend the range.

The MW noise is strong from longer distance, but VHF noise can be heard from 8-10 m.

I don’t know the exact band of this jammer I just tested it with my radio which has MW and VHF band. The jammer could also jam longwave band, or beyond vhf band too.

Warning! The flyback transformer generates high voltage, 15-25 kV (depends on power supply) It’s very dangerous if you pump high watts into the flyback. I accept no responsibility! The spark also produces ozone!

The jammer could also damage electronic devices from a few meters.

Using jammers is illegal!

You can experiment with making bigger flybacks by adding more secondary coils or making higher performance drivers to extend the range of this jammer.