DDS VFO Construction Manual – Issue 1
Page 8
4
C
ONSTRUCTION
4.1
G
ENERAL
The DDS VFO is a built on a high quality fiberglass PCB. The PCB is doubled sided with tracks on
both sides along with a ground plane. The holes are plated through and so it is not necessary to
solder both sides to make connections. To assist construction the component overlay is screen
printed on both sides and a solder mask is included to guard against solder bridges.
The ground plane is substantial and can sink quite a bit of heat from low wattage soldering irons
so ensure you use a good quality iron that can sustain the power required. You may find that
sometimes solder doesn’t appear to flow through to the top side. This is not necessarily a
problem because the plated through holes make a connection to the top side automatically.
Another point to consider is that plated through holes consume more solder than non-plated
holes and makes it more difficult to remove components.
The lesson is to double check the values and orientation of components before
installation.
There isn’t a ‘best’ scheme for loading the components, however, the suggested procedure is to
load the smaller components first and then work upwards.
4.2
C
ONSTRUCTION
S
TEPS
Refer to the parts list and Figure 2 when installing the components.
Step 1: Resistors
If in doubt check the values with a multimeter before soldering.
Pass the pigtails through
from the top and bend out slightly underneath to hold them in place. Turn the PCB over and
press down slightly to make them rest against the surface and then solder. Cut off the excess
pigtail with side cutters. The trimpot can also be installed at this stage. R14 is not used.
Step 2: RF chokes
These are not polarized and can go in either way. Make sure they sit flat against the board
before soldering.
Step 3: Capacitors
Install the capacitors with minimal lead length. The electrolytic is the only polarized capacitor
and the positive lead points towards the edge of the PCB.
