[Dstar] D-Star Digital Data

[Tony Langdon]

At 05:27 PM 9/2/2009, you wrote:
>Hi Everyone,
>
>After reading through the dstar.org.au website, I found that there is
>no frequency allocated for high bandwidth data (128kbps) on 70cm only
>23cm (1298.1000 MHz). Is this because of the fact that there currently
>no available gear with which to do this on 70cm? According to the LCD
>we can use wideband techniques above 430Mhz (or something along those
>lines), hence the 160kHz channel would be fine here.

Currently, DD is supported only on 23cm.  There is no 70cm equipment.


>Also what about using low bandwidth DD modes i.e. 4.8kbps on both 2m &

There is no "low bandwidth DD mode", there is only DD (128 kbps on 
23cm) and DV, which is simultaneous voice and data totalling 4.8 kbps.

>70cm, I am under the impression that this is possible using most
>current radios available, please correct me if I am wrong? Is there a
>frequency set aside for DD in 2m/70cm or is using the DV simplex
>frequency appropriate (as the radio should be able to distinguish
>between Voice & Data packets according to the spec)?

DV mode is simultaneous voice and data, so it's the same thing.  DV 
contains the following:

2.4 kbps voice, with 1.2kbps FEC (total 3.6 kbps).
Headers and other protocol overheads
Low speed data stream (no error correction) available for user applications.

>I currently do not own a D-Star radio but am making inquires about the
>operation and usage patterns as apart of an investigation for an
>Electrical Engineering Undergraduate Thesis. The title is
>"Investigation & Construction of a Software Defined Radio Repeater",

Interesting thesis. :)

>one of the options after getting a software FM repeater working is to
>investigate the feasibility of building a D-Star repeater or a hybrid
>(D-Star & FM).

Well, the utility of mixed mode repeaters is questionable, because of 
the informal nature of amateur communities.  There might be some 
circumstances where they'll fit in, but the key problem is the FM 
users not conflicting with the D-STAR users and vice-versa.  Amateurs 
are used to being able to hear all traffic on the frequency and join 
in when they wish to.  However, being able to convert the repeater 
from FM to D-STAR and back, manually, could be useful.

Building a D-STAR software defined repeater is entirely feasible, as 
you basically need to perform GMSK modulation and demodulation, and 
the rest is pushing data bits around.  With D-STAR, the RF side is 
only half the story, there's also the Internet infrastructure, which 
provides the long haul links between sites. :)

73 de VK3JED / VK3IRL
http://vkradio.com