On 11/20/2013 6:01 PM, Kai wrote:
I think that discussion should center around what the BW limit
shjould be for digital signals. The answer will likely be something
between 2200 Hz and 2800 Hz, because signals as wide as 2200 Hz are
already permitted. It's good to discuss this.
The discussion needs to extend *far* beyond hair-splitting between
2200 Hz and 2800 Hz. The discussions should include:
1) limits on the so called "semi automatic" operations that fire up
wherever and whenever they are called without any consideration
of other activity - activity that the calling station can not
hear.
2) limits on total occupied bandwidth - particularly in heavily used
(and shared) bands like 1.830-1.845, 3.570-3.600 MHz, 7.030-7.090
MHz, 10.125-10.150 MHz and 18.100-18.110 MHz - bands on which just
a few 2.5 KHz wide signals could dominate the entire "RTTY band"
3) If symbol rates are to be eliminated, so should the band limits
for "digital" operation and signals with greater occupied bandwidth
should be placed with other signals of similar occupied bandwidth.
4) requirements that all digital transmissions with more than 300 Hz
occupied bandwidth be identified in clear text using CW, ITA5 (170
Hz shift), or PSK31
5) requirements that stations engaged in automatic and "semi-automatic"
operation maintain a *listed* telephone whereby the licensee can be
notified of interference. a requirement that such interference be
be terminated within 10 minutes of placement of a call - not 10
minutes of retrieving a message.
6) requirements that any station using a digital modulation with
occupied bandwidth greater than 300 Hz include a functioning
"occupied channel detector" that prevents transmission if there is
*any* activity within 150% of the occupied bandwidth. Disabling
any "channel busy" detector would be presumptive evidence of
"intentional" interference.
7) requirements that all transmissions be in plain text - data
compression, if used, must be completely transparent so that
any portion of any transmission be readable in isolation.
The most important question is whether an occupied bandwidth greater
than 500 Hz is even justified for amateur digital operation. This
is after all the *amateur* service - not an alternative to the
internet or commercial common carriers.
73,
... Joe, W4TV
On 11/20/2013 6:01 PM, Kai wrote:
Thanks for the w8ji link. That was very instructional. But be careful.
The signal occupied bandwidth (what we presume to want to regulate)
does
not always relate to the noise bandwidth (which relates to
sensitivity). JT65 fro example sports a noise bandwidth of about 2.71
Hz (yes, Hertz), but an occupied bandwidth of 175 Hz. Furthermore when
operated as Joe Taylor intended at HF, you want to allow 2-4 kHz for
JT65 users because multiple simultaneous users in the the 2-4kHz BW are
decoded and presented to the user, just like in PSK31 (62 Hz/user).
The ARRL proposal does nothing more than to remove the archaic and no
longer relevant baud rate definitions of digital modes. They opted
instead to propose regulating digital signals by a maximum BW, and
chose
2.8 kHz to harmonize with the FCC/NTIA regulatikon already in effect
for
the 60m channels.
There are no changes to RTTY (which occupies 250 Hz per user at 170 Hz
shift and 45.45 baud - there are wider RTTY ham signals in use as well)
or how RTTY is used in contests.
Today under the present baud rate restrictions we already hear digital
signals as wide as 2,200 Hz in HF (PACTOR) and all is still right with
the world.
The Canadian ham regulators already limit all emissions in HF bands
below 28 MHz to 6kHz without regulating anything further about mode.
I think that discussion should center around what the BW limit shjould
be for digital signals. The answer will likely be something between
2200
Hz and 2800 Hz, because signals as wide as 2200 Hz are already
permitted. It's good to discuss this.
73,
Kai, KE4PT
On 11/20/2013 9:42 AM, David Cole wrote:
Al,
Thank you for that link! I now understand the dangers.
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