[Dstar] Encoded for the purpose of obscuring the meaning of the signals

[Tony Langdon]

At 05:38 PM 9/1/2008, you wrote:

>The section says "The licensee must not operate an amateur station to
>transmit signals that are encoded for the purpose of obscuring the
>meaning of the signals,"

This should answer your question in itself.

>D-STAR voice uses a method of encoding and decoding the audio waveform
>into a digital bit stream.  This method, or codec, is called AMBE.  This
>codec is closed to experimentation by amateurs because the specification
>of the codec is not available.  The codec has the purpose of obscuring
>the meaning of the signals, and the only way to decode the signals is
>with the purchase of an AMBE chip included in a D-STAR radio or dongle.
>It is not possible to decode the signals any other way.

No, the purpose of AMBE is to compress the voice into a 2400 bps 
(plus 1200 bps FEC) bitstream for transmission.  Yes, it is 
proprietary, but it is readily available in D-STAR radios and also 
the DV Dongle.  So the purpose is not to obscure the meaning of the 
transmission, simply to compress it down to a manageable bandwidth 
with acceptable voice quality.

Similarly, most digital radio systems use a "scrambler".  The purpose 
of this scrambler is again not to obscure the meaning of the message 
(i.e. encrypt it), but to prevent pathological bit sequences (i.e. 
long strings of 1's or 0's) from preventing clock recovery and 
synchronisation of the receiver.  The scrambling function is 
generally (1) well documented, and (2) built into _every_ compatible radio.


73 de VK3JED
http://vkradio.com