Configuring and Compiling the Morse Code Beacon

Two things need to be done to get the Morse Code Beacon up and
running.
 - The message payload needs to be set.
 - The frequency needs to be set and tuned (maybe).

Message Payload
~~~~~~~~~~~~~~~

Setting the message payload is the quickest and easiest task.  Open
the helper programe 'encoder.py' and edit the two variables at the top
to set the message and call sign.  The default message is "MOE " and
the default call sign is "N0CALL".

The message length can also be tuned.  It is measured in 'dot lengths'
and the default is 400, which is approximately 1 minute of
transmission time at the default speed of 8 wpm.

The program will convert the message to binary ones and zeros and
store them in an array of characters in message.h that gets compiled
into the main program.  Ones represent tone and zeros are silence.


Setting the Frequency
~~~~~~~~~~~~~~~~~~~~~

The transmit frequency is set in si406x.h, by setting the variable
RF_FREQ_HZ.

Because each actual device will differ slightly in its
characteristics, a header that is designed for a particular frequency
will be close, but almost certainly not right on.  For example, if
your header specifies 146.565MHz, it might actually produce a
signal at 146.559 MHz.  A receiver with a "discriminator center meter"
can easily verify this.

I found for the several boards that I've built that I needed to add
about 4KHz to get centered on the correct frequency.  So, to set my
transmitter to 146.565MHz, I used:

#define RF_FREQ_HZ      (146569000.0f)