JAMCAT

Description: This is a simple add-on jammer adapter for any amateur or two-way radio transceiver with an external microphone (PTT) and earphone/speaker connection. The jammer will transmit the radio upon detecting any activity on the frequency to which the receiver is tuned. This jamming system is intended to interfere with security guards, restaurant drive-throughs, corrupt police, or cellular/pager-type radio transmission systems. The circuit construction is straightforward. Two LM358 dual op-amps amplify and clip any audio signal from the jamming transceiver's earphone or speaker output. This audio signal triggers the transmitter portion of the transceiver. The circuit assumes that any noise from the earphone or speaker output indicates a valid transmission, so a tight squelch setting is necessary for proper operation. The op-amps amplify and rectify the incoming audio signal, converting it into a square wave. This square wave is further rectified to create a positive pulse that triggers a 555 timer in a monostable configuration with an adjustable delay time. The output of the 555 timer toggles a relay that controls the PTT switch on the jamming transceiver, causing it to transmit. The 1 megaohm Delay Time potentiometer adjusts the duration of the 555 timer's jamming time. A short jamming delay time may result in relay chatter, so a delay of a few seconds or longer is recommended. An optional internal noise generator consists of a standard 1N5235 6.8-volt Zener diode with a small reverse current and a 2N3904 transistor buffer. The National LM386 audio amplifier acts as a natural band-pass filter and small-signal amplifier. The noise jamming signal mixes with the PTT control line/microphone input to modulate the transmitter's RF output with random noise, masking the jamming transmission and making it appear as random noise to external observers. When the noise generator is disabled, the jamming signal will be an unmodulated RF carrier. The PTT control may require experimentation with the 1 kohm resistor value or checking the radio’s manual for the proper circuit, as some transceivers prefer a PTT-to-ground circuit while others need some resistance to ground. It is also possible to replace the PTT control relay with a transistor (2N3904, etc.), but the hardware relay provides more external control options when adapting to other equipment. The transceiver should be tuned to the desired frequency to jam. It is essential to consider that the goal is to jam the target's receiver, especially when using a repeater system. Optionally, connecting the transceiver to an external high-power RF amplifier or antenna system can enhance jamming effectiveness. The transceiver's earphone/speaker output jack should connect to the GBPPR JAMCAT's Audio Input, typically via a 1/8" mono jack, using the lowest volume possible. Care should be taken to avoid "speaker pops" when the radio unkeys, and pre-testing is advisable. The squelch on the transceiver should be adjusted to a tight setting, requiring a strong received signal to open, which helps eliminate random RF interference or noise and prevents unnecessary jamming transmissions that could reveal the jamming location. Any detected transmissions on that frequency will cause the C158A to transmit for approximately three seconds, controlled by the Delay Time potentiometer. The noise generator circuit may oscillate or output a very low noise signal; adjustments to the Zener bias resistor (2 kohm) may be necessary while observing the signal on an oscilloscope for optimal noise output. The LM386 can also oscillate without a good ground and proper power supply bypassing. Any Zener diode rated at or above 6.2 volts will function in the noise generator, as these diodes exhibit an "avalanche" region that generates substantial noise when properly biased. This circuit serves as a simple barrage (noise) jammer for VHF/UHF communications and is based on an old TV tuner with its local oscillator signal tapped and amplified, mixing the tuner’s voltage tune line with a sweeping, random noise signal.This is a simple add-on jammer adapter for any amateur or two-way radio transceiver with an external microphone (PTT) and earphone/speaker connection. The jammer will key (transmit) the radio on upon the detection of any "activity" on the particular frequency the receiver is tuned to.

This is the perfect type of jamming system to interfere with tho se pesky security guards, restaurant drive-throughs, corrupt police, or even LoJack and cellular/pager-type "quick bursting" radio transmission systems. The construction of the circuit is quite simple. Two LM358 dual op-amps are used to amplify and clip any audio signal coming from the jamming transceiver`s earphone or speaker output.

This audio signal is what is used to trigger the transmitter portion of the transceiver. The circuit assumes that any "noise" coming from the earphone or speaker output is the transceiver receiving a valid transmission, so be sure your radio`s squelch setting is tight or none of this will work properly and you`ll just be stuck jamming random signals! The op-amps are configured to amplify and rectify any incoming audio signal. This amplification and diode hard-limiting eventually turns the incoming audio signal into a square wave.

This square wave is further rectified to generate a positive pulse which is used to trigger a 555 timer in a monostable configuration with an adjustable delay time. The output of the 555 timer toggles a relay which controls the PTT switch on the jamming transceiver causing it to transmit.

The 1 megaohm Delay Time potentiometer can be adjusted to increase/decrease the length of the 555 timer`s "jamming" time. Note that too low of a jamming delay time can result in "relay chatter, " so set the delay time for a few seconds or longer.

The internal noise generator, which is optional, is just a standard 1N5235 6. 8 volt Zener diode with a small reverse current and a 2N3904 transistor buffer. The National LM386 audio amplifier acts as a natural band-pass filter and small-signal amplifier. The noise jamming signal is then mixed with the PTT control line / microphone input to modulate the transmitter`s RF output with a little bit of random noise. This will help in masking the jamming transmission, making it look like just random "noise" to an outside observer.

With the noise generator disabled, the jamming signal will be an unmodulated RF carrier. The only real "bug" in the circuit is the PTT control. Some transceivers like to be keyed with a PTT-to-ground circuit, while some require a little bit of resistance to ground. You may have to experiment with the 1 kohm resistor value, or check the radio`s manual for the proper PTT control circuit.

It`s also possible to replace the PTT control relay with a single transistor (2N3904, etc. ), but the hardware relay will allow for more external control options when adapting to other gear. Tune your transceiver to the desired frequency to jam. Remember, you want to jam the receiver of the target, so take this into account when a repeater system is being used. Optionally, connect the transceiver to an external high-power RF power amplifier (or antenna system) to increase the effectiveness of the jamming.

Connect the transceiver`s earphone/speaker output jack to the GBPPR JAMCAT`s Audio Input. This will usually be via a 1/8" mono jack. Use as low a volume as possible. Also watch out for "speaker pops" when your radio unkeys. Test ahead of time, if you can. Adjust the squelch on the transceiver to the desired setting. "Tight" squelches are best, that is, squelches which require a strong received signal before they "open. "This helps in eliminating the receiving of random RF interference or noise, and prevents any unnecessary jamming transmissions which could potentially reveal your jamming location.

Any detected transmissions on that frequency will cause the C158A to transmit for approximately three seconds, which is controlled via the Delay Time potentiometer. The noise generator circuit may break into oscillation or output a very low noise signal. If it does this, adjust the Zener bias resistor (2 kohm) up or down a few hundred ohms while observing the signal (disconnected from the LM386) on an oscilloscope for the maximum noise signal.

The LM386 can also oscillate without a good ground and poor power supply bypassing. Any Zener diode above or equal to 6. 2 volts will work in the noise generator as these Zener diodes have an "avalanche" region which generates a tremendous amount of noise when properly biased. Very simple barrage (noise) jammer for VHF/UHF communications. Based around an old TV tuner with its local oscillator signal tapped and amplified. The tuner`s voltage tune line is mixed with a sweeping, random noise signal.