OK so I have been wondering this for awhile, but the announcement of
the IC-9100 got me looking into it a bit further.
The FCC Rule for voice/image transmission emission standard is:
97.307f (1) No angle-modulated emission may have a modulation index
greater than 1 at the highest modulation frequency.
97.307f (2) No non-phone emission shall exceed the bandwidth of a
communications quality phone emission of the same modulation type. The
total bandwidth of an independent sideband emission (having B as the
first symbol), or a multiplexed image and phone emission, shall not
exceed that of a communications quality A3E emission.
Rules 97.307f (1) & (2) apply in the HF sub-bands for voice/image
communications
Rule 97.307f (2) applies to voice/image 29.0-29.7 mHz.
Now I'm not expert on modulation, but this does bring up an
interesting set of questions:
If we assume that DV is "Phone" communication, the D-STAR GMSK
modulation index is 0.5 with a deviation of 2.5 kHz. occupying the
approximate bandwidth of a 100% modulation (1.0 mod index) AM signal,
which is generally considered a legal transmission in those bands. To
my mind, that meets the requirements of 97.307f (1) and would mean
that a D-STAR signal should be legal on most US HF bands.
If we assume that DV is all or partially a "data" signal, we run into
a problem in the chart at 97.305c as the HF bands do not provide an
overlap between "data" and "voice/image" communications. Except of
course CW, which may be operated anywhere on the bands and that modern
"image" (fax/sstv) transmissions often include "data" elements to
designate modes - which I haven't seen any enforcement actions over.
(Let alone some other mixed mode operations.)
So, the big question is are people just assuming that D-STAR cannot
run outside of the 29.0-29.7 mHz. segment because FM uses a higher
modulation index and bandwidth or am I missing something in the
regulations? (Since D-STAR would seem to meet 97.307f (1) and be about
the bandwidth of an AM signal.) Certainly the AOR company believes
their product meets the regulations (with a narrower bandwidth) -- see http://www.hamuniverse.com/aorard9000mk2.html
Of course there is no indication that GMSK would do well in the HF
environment where signal are often contorted and twisted on their
journey.
John D. Hays
Amateur Radio Station K7VE
PO Box 1223
Edmonds, WA 98020-1223 VOIP/SIP: [email protected]
Email: [email protected]
