I'd like to make a circuit that is essentially a signal generator
producing a 400 kHz signal. I think this can be done with a
voltage source, resistor, capacitor, and inductor in parallel.
However, I'm not sure what values are appropriate for the
resistor, capacitor, and inductor. Any help is appreciated.
Thank you.
It would help if you'd specified what you wanted/needed this for.
The easiest, for someone wondering about inductors, would likely
be a crystal oscillator at some higher frequency, and then a divider
to get it down to the desired frequency. So a 4MHz crystal oscillator
and a decade counter would get you a nice 400KHz signal that only requires
wiring. Get one of those 4-pin ttl oscillators to take care of the
oscillator. You need to pick a frequency that will divide down to 400KHz,
unless of course you can live with some frequency close to that and then
you have a more open choice for the oscillator.
Someone mentioned ceramic resonators, and that would get you an exact
400KHz signal, though you might have to order the resonator. They are
right, you do see them in things, but I can't say how often I see them
so you might have to work through a lot of scrapped electronics before
you find one at 400KHz (though, again if you can live with something
a little different in frequency, you will have easier choices). You'll have
to wire up a crystal oscillator to use it.
Most common radios have a 455KHz (or more recently, 450KHz) intermediate
frequency, which means the IF transformers in them will likely be a good
start to an LC oscillator, though you'll need to add an oscillator, and
add some capacitance to tune the transformer down to 400KHz. And you have
to pull out the right one, since there will likely be 10.7Mhz IF
transformers in the same radios for the FM section.
If you don't need exactly 400KHz, you have more flexibility, since then
you don't have to worry about tuning it. If it just has to be somewhere
around there, the choices open up. If you need a sinewave, that will
change the solution.
Michael
