[amsat-bb] Re: BeeSat at 4800 GMSK

[Art McBride]

D-Star protocol is 4.8kb/sec for voice 1.2 kb for FEC and 1.2kb for data. It
is GMSK data, transmit rate is 3.6KHz max transmission rate, (7.2kb NRZ),
deviation is 1.8 KHz for a modulation index of 0.5.  BW per Carlson's rule
is 7.2 KHz 
A vocoder module provides for the voice compression. The Data side is used
for Call Sign, Name, City/ State, Brag Tape, GPS position, and Texting all
done with voice simultaneously. D-Star is not very successful in mobile
operation. I have had lots of conversations go R2D2 from a truck or car
passing me. From a fixed position range is surprisingly good. When used on a
Satellite this narrow mode I suspect is very sensitive to Doppler as well as
multipath. Circular antennas on both ends will solve multipath, but Doppler
shift must be dealt with.  
Art,
KC6UQH 

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Nathaniel S. Parsons
Sent: Saturday, April 10, 2010 10:02 PM
To: Tom Azlin N4ZPT
Cc: AMSAT-BB
Subject: [amsat-bb] Re: BeeSat at 4800 GMSK

Ah, thanks for clarifying. Unfortunately, if I understand you correctly, we
would have to talk to our satellite via digital voice, or at 128kbps, which
would be great if we could!

-Nate

On Sat, Apr 10, 2010 at 10:15 PM, Tom Azlin N4ZPT <n4zpt at cox.net> wrote:

> Well, make that the digital voice part of the protocol. The high speed
> digital data part is up to 128kbps which was not what I was thinking of.
>
> 73, tom n4zpt
>
> Tom Azlin N4ZPT wrote:
>
>> Hi Nate,
>>
>> the D-STAR protocol is only GMSK at 4800 bps and they selected a
>> time-bandwidth product of 0.5. 4,800 bps or 4k8 is perhaps not talked
about
>> as that IS the standard for D-STAR. So the software there might be
>> adaptable.  that is the reason I thought to suggest it.
>>
>> Good luck and 73, Tom n4zpt
>>
>>
>>
>> Nathaniel S. Parsons wrote:
>>
>>> Hi Tom,
>>>
>>> My mind had indeed played a trick on me, and I remembered MFSK as MSK.
>>>
>>> As far as the DStar group goes, I don't see any mention of 4800 bps or
>>> 4k8
>>> kbps on the public page, so if it's not the group's focus, I don't want
>>> to
>>> have to rely on that solution.
>>>
>>> Thanks,
>>> -Nate KC2SVI
>>>
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