VCO help needed.

[haig at cleo.murdoch.edu.au]

Greetings.  I'm new to this list and new to building so please bear with me.

To date I have only completed the +/-15v dc regulated power supply.  I'm in
the process of constructing the VCO labelled "National Semiconductor Appnote
AN-299: A temperature controlled exponential VCO" (I'm afraid I've forgotten
the source).  It has gone very well:  I have the basic breadboarded circuit
working.  I added trimmers at the LM329dz (to calibrate the reference
voltage to the required 6.9v), inline with the offset resistor, and (along
with a smaller  resistor) in place of the 250 ohm resistor near the "cv in"
for calibration of the range.

My main concern is with the comment that "An actual application would
include output decoupling".  Being new to electronics I'm not clear on this.
Does it refer to the fact that the ramp signal may be riding on a dc
voltage, and that it is this 'offset' which must be 'decoupled'.  If so
would a simple highpass filter (consisting of, say, a 0.47 uF capacitor and
a 1 MOhm resistor) at the 'ramp out' centre the signal at ground.

My other query is with the LM3046.  Apart from the limits imposed by the
required connections, does it matter which transistors in the package are
used.  I have left out the one with its emitter connected to the substrate,
as some directions I found indicated the substrate should be connected to
the lowest voltage in the external circuit.  When I connected the substrate
to ground there seemed to be no difference in the result.

Thats all for now.

Regards,
Callum.