3) A head-mounted binocular magnifier (the kind you
can flip up and down as needed). You can get an
inexpensive one from several vendors. All Electronics has
one for $4.95 (#HD-MAG); www.allelectronics.com.
4) A board vise (or something similar) to hold the PCB
securely while you work on it.
Before you start soldering the SMD chips, make sure
you've separated them into groups and tagged each group
with its value. You can use something like a hinged plastic
box that is divided into compartments, but make sure
the compartments can't leak into each other. Note: The
resistor chips are printed with numbers that show the
value (e.g., 103 = 10K), but the capacitor chips are not
marked. So be careful.
Once you've tinned the pads (remember: only one
pad per chip), you pick up a chip with the tweezers and
position it onto its set of pads. While holding it in place
with the tweezers, you heat the tinned end until the solder
melts and adheres to the chip. Let this cool. Remove the
tweezers and solder the other end. The chips are small, so
don't use too much solder. Don't hold the iron on the chip
too long. With a good iron, it should take just seconds.
It helps to use an iron with a steel-clad tip instead of
a solid copper tip. Be sure to keep the tip clean. The
traditional damp-sponge cools off the tip and can foul the
tip if the sponge burns. I much prefer a brass-wool pad. A
company called XYTRONIC makes them, and you can get
them from several vendors (Electronix Express #0603460).
I'm sure there is an officially correct way to solder
SMD chips that differs from my procedure. I'm just telling
you what worked for me.
After you've soldered all the SMD chips to the board,
clean off any flux residue with some rubbing alcohol and
an old tooth brush. Then give it a close visual inspection
with your binocular magnifier and look for bad solder
joints and solder bridges. Touch up any problems with
■ FIGURE 9
■ FIGURE 7
The Rest of the Parts
Mount the two-pin male header to the board and
solder it in place. Then mount the potentiometer, the
through-hole caps, the 78L05, the transistors, and the varactor. Solder them in place. The electret mic is polarized;
its metal case is ground. Be careful to insert it with the
positive end near R1. Don't push it flush; leave about 1/4
inch between the mic and the board. Solder it in place.
You need to solder a jumper to connect to the pad in
the center of the inductor (see Figure 7). Use a short piece
of insulated, solid hook-up wire — as short as is practical.
The length of the jumper adds to the inductance.
Again, clean off any residue and give the board a
good visual inspection. Make sure that the leads of the
through-hole parts are trimmed close to the board.
Mount the Antenna
To make a whip antenna, cut an 18 inch length
of 18 gauge magnet wire. Strip
about 1/2 inch of varnish
off both ends and
tin them. Bend one ■ FIGURE 8
end into an L shape for attachment to the board.
To blunt the other end, curl it into a tight loop and
solder the loop shut. About one inch away from
the L shaped end, make a three-turn coil by wrapping a
portion of the wire around a wood pencil (see Figure 8).
■ FIGURE 10