A Perfect Jammer


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Jammer Circuits / RF Circuits
This is a simple add-on adapter for any Family Radio Service (FRS), amateur, or two-way radio transceiver with a microphone/Push-to-Talk (PTT) and external earphone/speaker interface. It will turn the transceiver into a co-channel jammer. That is, a jammer which can only jam a single frequency upon the detection of any `activity` on that particular frequency. This type of circuit is also commonly referred to as a Carrier Operated Relay (COR). This is the perfect type of jamming system to interfere with those pesky Best Buy & Wal*Mart security guards, restaurant drive-throughs, police Mobile Data Terminals (MDT), and also LoJack and cellular/pager-type `quick bursting` radio transmission systems.
A Perfect Jammer - schematic

The construction is quite simple. A single LM324 quad op-amp is used to detect and amplify any audio signal coming from the jamming transceiver's earphone or speaker output. That audio signal is what is used to trigger the transmitter portion of the transceiver. It will be assumed that any `noise` coming from the earphone or speaker output is the transceiver receving a transmission, NOT just random squelch noise. So be sure your squelch setting is tight, or none of this will work properly and you'll be stuck jamming random signals. The four op-amps in the LM324 are configured to amplify, rectify and detect any incoming audio signal. This amplification and diode hard-limiting eventually turns the incoming audio signal into a square wave. This new square wave is then used to toggle a relay, which in turn, controls the PTT switch on the jamming transceiver - causing it to transmit. The TX Hold Delay Control Capacitor(s) can be increased/decreased to adapt to the desired jammer transmit time. The default value of 440 µF, two 220 µF electrolytic caps in parallel, holds the transmitter on for approximately three seconds. The noise generator, which is optional, is just a standard 6.8 Volt Zener diode with a small reverse current and a transistor buffer. The National LM386-1 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 frequency modulate the transmitter's RF output with a little bit of noise. This will help in masking the jamming transmission, making it look like random `noise` to an outside observer. With the noise generator disabled, the jamming signal is just an unmodulated Continous Wave (CW) RF carrier. The only real `bug` in the circuit, is the PTT control relay. Some transceivers like to be keyed with a PTT-to-ground circuit, while some require a little bit of resistance to ground. You'll have to experiment, or check the radio's manual, for the proper PTT control circuit. It is also possible, in some cases, to replace the relay with a single transistor (2N3904) or an opto-coupler (4N26). Operation Tune your transceiver to the desired frequency to jam. Example: 155.010 MHz Connect the transceiver to any external high-power RF power amplifier or antenna system that you may use to increase the jamming effectiveness. Connect the transceiver's microphone/PTT jack to the GBPPR JAMCAT's RADIO PTT CONTROL input. This will usually be via a 3/32` mono jack. Connect the transceiver's earphone/speaker output jack to the GBPPR JAMCAT's RADIO AUDIO INPUT. This will usually be via a 1/8` mono jack. Adjust the squelch on the transceiver to your desired setting. `Tight` squelches are best, that is, squelches which require strong received signals before they `break`. This helps in eliminating the receiving of random RF interference and preventing any unnecessary jamming transmissions, which could reveal your jamming location. Dick around with the volume / squelch / noise generator settings until it all fits your liking. Don't forget to properly power everything, dumbass.


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