6
LEDs
It is critical of course, to ensure correct LED orientation. The
cathode of the LEDs is indicated by the flat on the body of
the LED. However, on 3mm LEDs the “flat” is not so easy to
see (though quite clear, using magnification). So note that
the cathode is also indicated by the shorter wire (before
you’ve cut them!) and also by the larger electrode. The
larger electrode can be seen clearly if you hold the LED in
front of a strong light. The diagram to the right illustrates the
three ways of identifying the LED cathode.
In actual operation using the patch antenna (not externally mounted active antenna), the patch antenna is
fitted on the solder-side of the board (see next section). This side will be facing up so that it has a good
view of the sky. In this case, it is helpful to install the three LEDs on the component-side of the board. The
side without the silkscreen printed component outlines. This will ensure that you can see the LEDs in
operation.
If you are using an external active antenna, then you could continue to u
se the LED’s on the component
side of the board. Additionally, 2 x 3 header connection pads are provided, in case you want to wire the
LEDs to be mounted off-board, for example, to fit into an enclosure or front panel (headers not supplied).
Regardless of whether you wish to have
the LEDs fitted on the component or
solder side of the PCB, you need to
ensure the flats (cathodes) of the LEDs
are aligned with the silkscreen on the
PCB. The cathodes/flats/short-wires are
inserted into the PCB holes nearest to
the PCB centre.
This photograph shows the usual method
of assembly, with the LED’s on the
solder-side of the PCB so that with the
patch antenna installed on-
board, they’ll
be visible.
Patch antenna installation
The supplied 25 x 25mm patch antenna has been custom-manufactured, with tuning to match it to the
characteristics of this PCB. The tuning is indicated by the small cuts you may be able to see in the metallic
surface of the top side of the patch antenna.
Do not be tempted to substitute another patch antenna,
which will not have been tuned to match this PCB layout!
To install the patch antenna, first
remove the plastic film that
protects the self-adhesive sticker
on the underside of the antenna,
as shown in these two
photographs (far right: after
removal).
