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This discussion has probably gone on too long, but here are the
defining documents. "Law" in this case comes from congressional
establishment and empowering of the Federal Communications
Commission. In general "Part 97" is what we as hams refer to for our
permissions and obligations. The most relevant part of the FCC's
regulations, so far as I see is:
<blockquote type="cite">
<p class="MsoNormal"><span class="fontstyle01"><span style="mso-ansi-font-size:
12.0pt;font-family:ArialMT">Title 47: Telecommunication...</span></span></p>
<p class="MsoNormal"><span class="fontstyle01"><span style="mso-ansi-font-size:
12.0pt;font-family:ArialMT">PART 97—AMATEUR RADIO SERVICE...</span></span></p>
<p class="MsoNormal"><span class="fontstyle01"><span style="mso-ansi-font-size:
12.0pt;font-family:ArialMT">§97.113 Prohibited
transmissions.</span></span><b><span style="mso-bidi-font-size:8.0pt;font-family:Arial-BoldMT;color:black"><br>
</span></b><span class="fontstyle21"><span style="mso-ansi-font-size:12.0pt;
font-family:ArialMT">(a) No amateur station shall transmit:</span></span></p>
...
<p class="MsoNormal"><span class="fontstyle01"><span style="mso-ansi-font-size:
12.0pt;font-family:ArialMT">(4) Music using a phone emission
except as
specifically provided elsewhere in this section;
communications intended to
facilitate a criminal act; messages encoded for the purpose
of obscuring their
meaning, except as otherwise provided herein; obscene or
indecent words or
language; or false or deceptive messages, signals or
identification.</span></span></p>
</blockquote>
As others have pointed out, that phrase "<span class="fontstyle01"><span style="mso-ansi-font-size:
12.0pt;font-family:ArialMT">messages encoded for the purpose of
obscuring their
meaning" is what matters.<br>
<br>
</span></span>The "except as otherwise provided herein" has
sometimes resulted in challenges as new technologies came along.
E.g. when sending images perhaps as JPEG within something like the
Winlink protocols for sending email, or simply television or
radio-teletype transmissions, someone listening to the transmission
would not understand the meaning but these are allowed. Sometimes
these new technologies have been controversial, e.g. there were
recent complaints by some hams about others using compression and
noise reduction techniques such as FT8. I am not at all a lawyer
but I think the essence here has been that it is OK so long as ways
to "decode" a transmission are publicly available. Some of the
exceptions have been put in for things such as remotely controlling
satellites, clearly not considered in the original rulings!<br>
<br>
Regarding the "to keep hams from competing with commercial carriers"
argument, there is this in the regulations immediately after the
above, and still within "<span class="fontstyle21"><span style="mso-ansi-font-size:12.0pt;
font-family:ArialMT">No amateur station shall transmit</span></span>"
<blockquote type="cite">
<p class="MsoNormal"><span class="fontstyle01"><span style="mso-ansi-font-size:
12.0pt;font-family:ArialMT">(5) Communications, on a regular
basis, which could
reasonably be furnished alternatively through other radio
services.</span></span></p>
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Bob Wilson, WA9D<br>
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