Ok folks, lets get the VFO built.
Some quick theory first, more to follow tommorow (I'm tired ;-)
A schematic of the VFO only is available at
http://reality.sgi.com/adams/vfo.jpg (Thanks Chuck)
VFO stands for variable frequency oscillator. The VFO determines the
frequency at which the radio operates. The vfo signal is mixed with the
incoming RF to convert the desired receive frequency to the IF
(Intermediate Freq.) of 4MHz. It also determines the transmit frequency
by basically the opposite function.
There are 3 things that you need to make a VFO (or any oscillator) work.
You need gain (amplification), feedback from output to input in phase,
and a frequency determining device (or network).
Lets get it built.
Find and install the following components (with the power off)
c2 47 pf
c3 10 pf
c4 2700 pf
c5 2700 pf
c6 3300 pf
c8 82 pf
c9 10 pf
c10 270 pf
c103 .01 mf
c105 .01 mf
L1 (You did finish it, right? ;-)
R15 47 kohms
R16 22 kohms
R17 2.2 kohms
R18 1 megohms
Install a jumper between J2 pins 2 and 3. You can use a resistor lead
that you trimmed from one of the above components. This temporarily
takes the place of the tuning pot, which will be mounted later.
When you finish, double check the component placement. Also check your
Fire it up! Put your RF probe on the base of Q2. You should see some RF
voltage. Those with oscilloscopes or frequency counters should see an
approximatly 3 Mhz signal here. The circuit will be calibrated later so
don't install c7.
Get this portion built, and stay tuned for a circuit description, spice
analysis and some experiments. Bed time!