[Dstar] questions from ZL2DW

[Tony Langdon]

At 07:05 AM 8/27/2008, you wrote:
>Hello guys
>please excuse my ignorance here but can someone(s) please give me 
>your thoughts and observations re dstar.

I'll add my 2 cents worth as a user, though I'm sure the gurus can 
add more to my reply.

>  I have been subscribed to this reflector for months now and mostly 
> what I have seen relates to site interconnect problems.
>Here in ZL we have only one dstar repeater and it's not on a hilltop 
>yet..........and won't be within my 70cm range when it is.
>So when it is operational what can those within its range  expect to 
>do with this dstar stuff, will it be somewhat like a digital form of 
>IRLP.......or what ?

D-STAR is quite a different beast to IRLP.  While it can do some IRLP 
like functions, native D-STAR is based on the concept of source 
routing, where you specify the destination you want to communicate 
with, the local RF port and the local gateway to use (these 
parameters are configured into your radio).  Also, D-STAR DV (digital 
voice) mode has a simultaneous data channel of the order of 1kbps 
(throughput similar to 1200bps packet radio).  This data channel can 
be used for chatting, D-PRS GPS data, file transfers and many other uses.

Then there's DD mode (on 1.2 GHz only), which offers 128kbps data over the air.

>Why dstar and not P25 or Tetra ?

Cost, and D-STAR's gateway architecture is much better developed than 
the other alternatives.  On the global front, several P25 advocates 
"converted" to D-STAR, because D-STAR has a working worldwide gateway 
implementation and a rich feature set.  At least one of those now 
runs a D-STAR gateway.  D-STAR's feature set, while not perfect, is 
geared towards amateurs, not commercial 2 way radio systems.

>Is there a really good lay mans web site I can go to to read/learn 
>more about dstar and can someone please comment on the dstar gear 
>just working as a conventional repeater, how does it sound, how does 
>the range compare with an analogue repeater on the same band.?

Well, www.dstar.org.au is one place to look, to see how things are 
going over this side of the ditch.  There's some introductory 
material there as well.  As for sound, it's not going to go close to 
a well setup FM repeater - vocoder artefacts are readily 
apparent.  However, the audio is generally easy to copy, just sounds 
a bit "unnatural" or "metallic".  Personally, I don't mind it.  As 
for range, quantitative measurements done by the Utah VHF Society 
suggest that digital range is very slightly less than FM, but that's 
taking the 12dB SINAD point as the FM reference, which is quite a 
noisy signal.  In practice, weak D-STAR signals sound much better 
than weak FM signals, because D-STAR is noise free down to the 
digital threshold.  You do get some strange noises (colloquially 
called "R2D2" ;) ) when the bit error rate starts to climb, before 
the signal drops out altogether.  Mobile performance can sometimes be 
a bit affected by multipath, which causes R2D2 earlier than you get 
while stationary.  For this reason, I'd love to see D-STAR on 6 metres one day.

>Does dstar have a future or will it have a successor ?

Hmm, my crystal ball is cloudy, but D-STAR is experiencing rapid 
growth around the world at this time.

>Are there ever going to be other manufacturers, other than Icom ?

That's something I would love to see.  However, there are other 
people manufacturing non radio gear (e.g. the DV Dongle) that works 
with the D-STAR network.

>Like I said please excuse my ignorance but I'm keen to learn and 
>some of these question may seem a bit derrrr.
>Many thanks and 73, David Walker (ZL2DW Hastings, New Zealand).

Actually, all good questions, and I hope other people chip in as well.

73 de VK3JED
http://vkradio.com