[amsat-bb] Re: Icom D-Star

Tony Langdon vk3jed at gmail.com
Sat Apr 23 14:42:08 PDT 2011

At 04:42 AM 4/24/2011, Gordon JC Pearce wrote:
>On Sat, 2011-04-23 at 10:42 -0500, Gregg Wonderly wrote:
> > In the end, digital compression of spectrum space is going to 
> happen more and
> > more.  AM style broadcast is hugely inefficient even though it is 
> painfully
>Okay, but *why*?  Why are we so obsessed with squeezing bandwidth down
>and down, at the expense of intelligibility?

I find D-STAR more intelligible than a significant proportion of FM 
transmissions.  And why are we obsessed with reducing bandwidth?  2 reasons:

1.  It's economics, bandwidth is expensive in the commercial world, 
and in the ham world, some countries are suffering congestion.

2.  Reducing the amount of information to be transmitted means more 
range (Shannon's Law).  And don't we all want a bit more range in the 
ham world?

>I've got my spectrum analyser hooked up to my 2m aerial at the moment.
>For the past half hour it has indicated the odd little spike at
>144.800MHz indicating a little bit of (weak) APRS traffic, a big spike
>at the output of GB3CS (because it's line-of-sight), a couple of
>slightly smaller spikes from the other two local repeaters (PA and KE)
>and a bump where FE, FF and AY are supposed to be (they're quite weak

Well, everyone's in a different situation.  I have had days in 
Melbourne where it's hard to find a free 2m simplex frequency.  I'm 
certain in the US there's places where 2m is congested.  Sure, where 
I am now, 2m is fairly quite, but I'm outside the big cities, and 
separated from Melbourne by a mountain range.  With only a few dozen 
hams in the area, bandwidth usage isn't a high priority issue, but 
that's not going to stop me playing with narrowband voice modes.

>This is where D-Star falls down - it's *still* just a 12.5kHz-wide
>channel.  Without getting into linear PAs and the like, it's going to be
>quite hard to do anything else and have a useful data rate.

We do have linear PAs available on VHF and UHF...  We could always do 
FDMDV on 70cm to really save bandwidth. ;)

73 de VK3JED / VK3IRL

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