[OZAPRS] Is it life and death.

[Chris Hill]

Hi Hamish,

I think you'll find it's even worse, as 300bps HF packet is normally
generated without any attempt to maintain phase coherency during the
transition from one tone to the next.

By contrast, the G3RUH et al 9600bps FSK is actually Coherent-Phase,
Frequency Shift Keying (CPFSK), hence the measured occupied bandwidth is
indeed close to the theoretical bandwidth (shift = 6kHz, being between
-3kHz
deviation and +3kHz deviation, and baud rate = 9.6kSps, hence occupied
bandwidth =~ 16kHz...  just enough to squeeze into a standard 16k0F3
channel).

Anyway, as you point out, 300bps HF packet occupies more than just the
"MARK" and "SPACE" frequencies.  All the more reason to take the effort to
ensure we are, indeed, on frequency.


Regards,




Chris



-----Original Message-----
From: ozaprs-bounces at marconi.ics.mq.edu.au
[mailto:ozaprs-bounces at marconi.ics.mq.edu.au]On Behalf Of Hamish Moffatt
Sent: Saturday, 3 April 2004 12:57 PM
To: ozaprs at marconi.ics.mq.edu.au
Subject: Re: [OZAPRS] Is it life and death.


On Sat, Apr 03, 2004 at 12:09:00PM +0800, Chris Hill wrote:
> For tones of 2110Hz & 2310Hz, and a suppressed carrier frequency of
> 10147.6kHz, an amateur can be transmitting 100W of RF on 10.14991kHz.
> That's 100W of RF energy, less than 90Hz from the band edge.

With 300 baud FSK transmissions I think you will find that the sidebands
will be out of band in that case. The two tones are within the band but
the act of shifting between them creates sidebands.

According to http://cnx.rice.edu/content/m0545/latest/ the bandwidth
is the frequency shift plus the baud rate (for the worst case,
alternating 1s and 0s) for FSK, meaning 500 Hz wide.

Your tones need to be at least 150 Hz from the band edge to be legal.


Hamish
--
Hamish Moffatt VK3SB <hamish at debian.org> <hamish at cloud.net.au>
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