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SEE BELOW.....<br>
<br>
<br>
Frank or Barbara Rossi wrote:
<blockquote cite="mid:4A417991.2000701@bellatlantic.net" type="cite">
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Looks like IARU-Region 1 Band plan is way to restrictive <a moz-do-not-send="true" href="http://www.ari.rc.it/Download%20vario/bandplan.pdf">Click</a>
<a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://www.ari.rc.it/Download%20vario/bandplan.pdf">http://www.ari.rc.it/Download%20vario/bandplan.pdf</a><br>
With all the restrictions, there will be no APRS on 30 Mtrs.<br>
So much for a world wide band plan.<br>
N3FLR - Frank<br>
<br>
On 6/23/2009 6:37 AM, G0JXN Jim wrote:
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<div><font face="Arial" size="2">Hi Guys</font></div>
<div> </div>
<div><font face="Arial" size="2">The UK Amateur Radio license no
longer allows the operation of an APRS digipeater without special
permission (Notice of Variation) from the regulator (Ofcom). It being
filtered first through the RSGB.</font></div>
<div> </div>
<div><font face="Arial" size="2">I wish to run a digipeater on
10.151MHz (KAM) but am advised the it would probably not be recommended
by the RSGB because the bandwidth of 300bd would exceed the 500Hz laid
down in the IARU bandplan for 30m. The implication being that we should
not operate APRS on 30m at all.</font></div>
<div> </div>
<div><font face="Arial" size="2">Monitoring signals on 30m I find
that they all seem to be within 400Hz but I will need to prove that on
paper.</font></div>
<div> </div>
<div><font face="Arial" size="2">Can anyone please tell me what the
bandwidth will be for a properly adjusted 300bd station and how this
might be calculated?</font></div>
<div> </div>
<div><font face="Arial" size="2">73</font></div>
<div> </div>
<div><font face="Arial" size="2">Jim, G0JXN</font></div>
</font></div>
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</blockquote>
<br>
<br>
See my previous response to this thread under the heading:<br>
"Re: [aprssig] APRS Bandwidth - Carson's Rule Recalculated"<br>
below.<br>
<br>
300 baud / 200 Hz shift AX.25 packet is perfectly capable of fitting
into a 500 Hz occupied bandwidth. Aside from the issue of "unattended
operation" mentioned in the bandplan document mentioned above, I don't
see any problems. HF APRS is certainly far less disruptive than the
Pactor III being used with the AirMail mail box system on HF. <br>
<br>
<br>
<br>
Keith VE7GDH wrote:
<br>
<blockquote type="cite"><br>
Regarding 500 Hz bandwidth... aren't 300 baud tones just 200 Hz apart?
<br>
I viewed the reply from Chris G4HYG about Carson's rule...
<br>
<a class="moz-txt-link-freetext" href="http://en.wikipedia.org/wiki/Carson_bandwidth_rule">http://en.wikipedia.org/wiki/Carson_bandwidth_rule</a>.
Doesn't that apply
<br>
to FM? See
<br>
</blockquote>
<br>
You are partly correct. Carson's rule applies to modulating audio or
data frequencies applied to an FM transmitter. <br>
<blockquote type="cite">For SSB, I would have thought the 200 Hz
difference between
<br>
the two tones would set the bandwidth.
<br>
<br>
</blockquote>
<br>
Sending FSK data with an SSB transceiver is more like FM than SSB. <br>
Applying a single audio tone to the mic jack of an SSB rig creates a
single RF frequency offset from the (suppressed) carrier frequency by
the frequency of the audio tone. <br>
<br>
<br>
Applying an audio tone 200 Hz higher to to the SSB rig will create a
single RF frequency 200 Hz farther away from the (suppressed) carrier
frequency. <br>
<br>
<br>
The net effect is exactly the same as if you have a single key-down CW
carrier and shift it 200 Hz periodically (i.e. direct FSK with a 200 Hz
shift) <br>
[Some, mostly higher end, HF transceivers actually offer this
direct FSK mode. Rather than having feed alternating audio tones into
the mic jack, you feed a TTL-logic-level 300 baud (for packet) or 45
baud (for RTTY) data stream directly into a special FSK input on the
radio.] <br>
<br>
<br>
The bottom line is that you essentially have a FM (i.e. constant
envelope power) transmitter modulated by 150 bps square waves rather
than rather than higher-frequency audio sine waves. <br>
<br>
<br>
[Note that "300 baud" (300 bits / second) corresponds to only 150 Hz
square waves. Assuming the worst case of alternating "1"s and "0"s,
each square wave cycle will require TWO bits to complete -- not one
since one bit has to be the high half of the square and next bit the
low half. Any bit pattern that has adjacent "1"s or adjacent "0"s will
have a lower effective "squarewave frequency". ]
<br>
<br>
In either case, the occupied bandwidth is greater than just the the
spacing between the two tones (a.k.a. "mark" and "space" frequencies).
This is due to the transients created during the instantaneous shift
from one frequency to the other. [Even CW transmission has a
bandwidth greater than a single frequency when you start keying at a
rate higher than zero!]
<br>
<br>
The original poster that applied Carson's rule for approximating
occupied FM bandwidth forgot that the base band modulating "frequency"
would be 150, not 300 Hz. Recalculating the occupied bandwidth,
<br>
<br>
2 (100 Hz deviation + 150 bps) = 500 Hz. <br>
<br>
<br>
Considering that the actual data "frequency" is actually lower than
150 Hz since runs of 2 or 3 ones or zeros DO frequently occur, the
actual average occupied bandwidth is actually lower. <br>
<br>
[Note that the occupied bandwidth created by true square-wave
modulation would be greater than for sine waves. However, the finite
bandwidth of the SSB modulator and IF filters "rounds off" the corners
of the square waves and increases the rise/fall time to be more
trapezoidal than square, resulting in a bandwidth nearly the same as
with sine waves.]
<br>
<br>
I can attest to the fact that this is "REAL" since I have no difficulty
receiving 200 Hz HF packet through an 500 Hz bandwidth CW filter on HF
transceivers.
<br>
<br>
<br>
------------------------------------------------------------------------
<br>
<br>
--
<br>
<br>
Stephen H. Smith wa8lmf (at) aol.com
<br>
EchoLink Node: WA8LMF or 14400 [Think bottom of the 2M band]
<br>
Skype: WA8LMF
<br>
Home Page: <a class="moz-txt-link-freetext" href="http://wa8lmf.net">http://wa8lmf.net</a>
<br>
<br>
JavAPRS Filter Port 14580 Guide
<br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/aprs/JAVaprsFilters.htm">http://wa8lmf.net/aprs/JAVaprsFilters.htm</a>
<br>
<br>
"APRS 101" Explanation of APRS Path Selection & Digipeating
<br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/DigiPaths">http://wa8lmf.net/DigiPaths</a>
<br>
<br>
Updated "Rev H" APRS <a class="moz-txt-link-freetext" href="http://wa8lmf.net/aprs">http://wa8lmf.net/aprs</a>
<br>
Symbols Set for UI-View,
<br>
UIpoint and APRSplus:
<br>
<br>
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