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MHz frequency source with selectable internal amplitude
I needed a
frequency reference for tuning up the RS-232 to 100 MHz RF desktop
adapter elsewhere on this site, when I found this Saronix crystal
oscillator in my junk box. A few minutes with AVRStudio produced
an ATtiny12 to make a tone - even fewer parts than using an NE-555.
With the addition of a transistor to gate the output, I was set to go.
Quick and dirty, but it was useful.
oscillator has an open emitter output. When the 330 Ohm load
resistor on the output is grounded, the RF out of the oscillator
increases. Modulation is affected by driving the MPSH34 on and off to
switch the 330 Ohm load resistor. An Atmel ATtiny12 provides a square
wave signal that can be used to drive the MPSH34, or if the SPDT
switch is in the other position, an external modulation source can be
used to modulate the signal, or if nothing is connected to the
modulation input, the RF output is at maximum value because of the
two 10K pull-up resistors on the base of the MPSH34. This technique
should work with an oscillator that requires an external pull-down
resistor on its output.
construction, and probably a more practical one would be to use an
NE555 or somilar for the oscillator instaed of a microcontroller for
the modulation souce.
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