An idea for a short-range wideband transmitter would be to take a PLL-controlled CB, unhook the VCO from the PLL chip, and use an oscillating voltage (sin wave, triangle wave, or sawtooth) to drive the VCO. To keep the CB within a certain band, just set the peak voltage of the oscillator output and adjust the VCO coil. Using a sawtooth generator of about 1khz would sound almost like a constant roger beep tone across the entire transmitter band, because you'd essentially be sending a quick pulse of RF on every frequency at a rate of 1000 times per second. VERY effective jammer in theory.
Another idea is to just overmodulate the heck out of a CB or export that uses pure solid state AM regulator modulation (NOT a 148 or similar that uses a transformer driving a regulator). Use a resistor in the driver's collector circuit or base circuit to control the output level. Modulate the radio with about a 1khz tone, and completely disable the AMC. The extreme audio harmonics, combined with normal Intermodulation Distortion, will modulate the carrier over a VERY wide range, making a reasonably effective jammer which can be limited in range with careful driver control. This would be extremely effective on the specific channel to which its tuned, and gradually less effective the further away from that channel you went.