HFU HF Underground
Technical Topics => The RF Workbench => Topic started by: Beam Tetrode on December 23, 2016, 0356 UTC
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I need a bit of guidance with my latest RF project and it's something I cant really ask my Ham buddies about.
(http://www.next.gr/uploads/4/tv-and-fm-jammer-schematic-using-2n2222.jpg)
I built this VHF Jammer as a gift for my sister, she works in a small office with a colleague who likes to play the radio too loud.
Long story short; the guy is a jerk and wont turn it down and the HR officer is the guys buddy and isn't really doing anything about it.
As a caring brother this situation makes my blood boil so I've decided to help her.
I prototyped the circuit on perfboard, it worked but with a lot of frequency drift.
Next I designedand etched a simple PCB and soldered it all together.
(http://i.imgur.com/e26Mqr1.png?1)
(http://i.imgur.com/VRGPQ8o.jpg?1)
(http://i.imgur.com/zMqG3wg.jpg?1)
Problem is it still has really bad drift.
This is the first PCB i have designed for an RF project so I am wondering if I did something obviously wrong.
I would appreciate any input I can get here.
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First and foremost, you need a regulated voltage supplying the oscillator. At this power level, a dropping resistor and a zener diode of 6V should work. I would also add a buffer stage and a small piece of wire on the output for an antenna. These two changes will help a lot to stabilize the oscillator. Alternatively, you could modulate the oscillator with a sawtooth waveform which would be more annoying to the 'victim'.
Good luck,
+-RH
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Alternatively, you could modulate the oscillator with a sawtooth waveform which would be more annoying to the 'victim'.
Sawtooth through a varactor diode as half the tuning LC circuit to sweep frequencies around the range you desire, nasty thought :P
That is definitely one way to piss off some people.
redhat is right though, you should use either a zener diode and resistor to regulate voltage going into it or even something as simple as a three leg 5v regulator like a 7805 so that the free running oscillator doesn't drift around.
It's funny because as simple as this circuit looks, this is the one place where engineers start pulling hair because LC oscillators are the most finicky part of a far more complex RF circuit.
Want to get real nasty I recommend a push pull oscillator at half the frequency which runs in anti-phase to get up to the frequency you want to block. Far more stable and will create enough blackout at the frequency if you want to get in some trouble.
In all practicality though wouldn't it be easier to use an FM MP3 player transmitter set to the channel you hate and want to block? Add a piece of wire on the circuit for an external aerial and you're set. Run some fart noises into the audio input to annoy further, and remain somewhat legal doing so.