VEC-1220K/1230K/1240K/1280K Owner's
Manual
15
This concludes the first phase of construction (small generic parts). Next, you'll
install frequency-determining components. However, before you start, this
might be a good time to take a well-deserved break! Be sure to check transistor
and diode positioning and polarity before moving on.
Phase 7: Frequency-Determining Parts
In this section, you'll select a
specific set of instructions for your particular kit
(VEC-1220K, VEC-1230K, etc). However, before you do this, please review
these two important general construction tips that apply to all four models of the
kit.
Installing Multilayer Capacitors:
There are 8 multilayer capacitors in your kit.
A multilayer cap is similar to a surface-mount "chip" capacitor, except that it has
a lead spot-welded onto each end of the capacitor body. Each cap is then
coated with an epoxy coating. Multilayers have superior radio-frequency
operating characteristics, but the lead welds may fail if the leads are placed
under stress while being heated during installation or removal. For this reason,
never use force to seat a multilayer cap
into the PC board. If the spacing isn't
right, pre-form the leads to the correct spacing before installation!
Incorrect
Ooops!
Correct
Winding and Installing Toroid Coil L1:
The transmitter's low-pass filter uses
a high-Q toroid inductor wound on a T37-2 form (T37 means the powdered-iron
form is .37-inches in diameter). When winding L1, the number of turns are
counted
inside the form (
not on the outside). This means, if the instructions call
for a 12-turn coil, you must
pass the wire through the center of the core
12
times.
When winding this coil, be sure to pull each turn up tight before starting the
next. If the coil is wound loosely, its inductance increases--a condition that may
reduce transmitter output power.
Count turns on inside of form.
Tin leads with solder before installing.
Pull each turn tight before winding the next.