First post, although I've been lurking around for the past 18 months. I have caught the electronics bug, and have gradually built up a small hobbyist lab including a Fluke 17B, Rigol DS1102E and a cheap Tenma power supply. I've been gradually teaching myself stuff, and learning how to use particular components. As part of this process I have been constructing an FM Jammer, and have now encountered a difficulty in designing an improvement to the project.
The jammer uses a 555 to generate a ~kHz square wave which modulates the base of a 2N2222 transistor. The collector of the transistor is connected to an LC oscillator tuned to MHz FM radio frequencies. A similar FM jammer can be found at
http://www.circuitdiagram.org/555-tracking-transmitter.html. FOr my version I have left out the trim capacitor and instead vary the supply voltage to tune the circuit.
The circuit works very well, and my use of the supply voltage to tune the circuit gave me an idea. If I supplied the cicuit with a saw tooth voltage (5V to 10V ramp at ~1Hz) then the circuit would scan across the radio spectrum, creating a broad spectrum jammer and saving the need to tune it.
So, I thought I would use a 555 again to generate the supply voltage as a saw tooth. Using a transitor based current source to charge a large (1500uF) capacitor, with the 555 set to discharge the capaitor through pin 7 when the capicitor raches 2/3 of the supply voltage, and then allow recharging from 1/3 of supply voltage. This was based on a circuit from
http://www.electronic-circuits-diagrams.com/oscillatorsimages/oscillatorsckt2.shtml, but with a bigger capacitor (and corresponding resistor). This circuit worked fine on its own, generating a nice saw tooth from 5V to 10V when I connected a 15V supply. I now hooked it up to my FM jammer as the power supply to the FM jammer.
I had hoped that by using a larger capcitor on the 555 saw tooth supply, it would be able to supply the FM jammer with the required current. However, it just doesn't work: as soon as I connect the 555 saw tooth to the FM jammer, the saw tooth disappears. I assume there is a limit to how big a capcitor it is wise to use since it much discharge through the 555, so I'm not going any bigger at the moment.
Can anyone suggest where I am going wrong, or indeed a completely different starting idea for supplying a saw tooth. I'm really after a simple solution I can build and understand (even if it doesn't work too well) rather than a perfect solution that teaches less.
Cheers