I have finally completed the building of a12 channel switch
selectable CTCSS Tone Encoder. Now, I'll be
able to access the various repeaters with my old Midland Model
13-510 two meter rig. Each of the 12 channels can be
adjusted to any frequency tone between the ranges of 67.0 Hz to
254.1 Hz, to suit one's individual needs.
The circuit uses a 555 timer chip to generate the tones.
Since the chip outputs square waves, it is followed by a nine
element Chebyshev* integrater/filter which converts the square waves to
sine
waves. Because the filter has a 26 dB insertion loss, it is
followed by
a LM386N-1, 25 dB gain
amplifier whose output is transformer coupled and affords an ample but
fully adjustable level (2000 ohm output) to the transmitter's FM
modulator.
This tone generator requires a +12 volt, 15 mA DC power supply and of
course, the tone connection into the rig, beyond the speech
pre-emphasis circuits, for proper operation.
If anyone is interested in obtaining the tone generator circuit
diagram, drop me a line.
