[aprssig] APRS and dstar

[Stephen H. Smith]

On 5/27/2012 9:55 AM, Jason KG4WSV wrote:
>
> Not being a naysayer, but what value does APRS add to this equation?
> Sounds like we all need to switch to DSTAR, and build "DVRS" instead
> of "AVRS"?
>
>
> My personal hangup with DSTAR is the price of the hardware (especially
> when I consider the price of the APRS gear I already have).  I can
> throw together a small APRS tracker for a rocekt, balloon, or vehicle
> for cheap; not so with DSTAR.
>
>

Not to mention the infamous "digital cliff"; i.e. the all-or-nothing nature of 
digital transmission formats.  Essentially there IS NO fringe area where a 
signal is scratchy or noisy but still useable.   To get usable coverage 
comparable to existing analog repeaters, including the  
marginal-but-still-usable   fringe areas (i.e. without the hiccupping, 
stuttering, drop outs, beeping and bonking of digital systems at the fringe), 
you will need TWO to THREE times as many repeater sites.

A decade ago, I was involved in the review of the design proposal for the 
next-generation public-safety network for Los Angeles County sheriff and fire, 
presented by a major RF systems design house.    The still-current (analog) UHF 
system transmits from 17 sites and receives from around 30-40 around the 
county.   The proposed digital system (with a quite conservative and realistic 
design approach)  would have required 117 sites (!) to achieve about the same 
coverage.     The county is still reeling in sticker shock at the HALF-BILLION 
(2001) dollars this network would require to build.

This issue is only now beginning to be realized in all the excited frenzy of 
talk about a nation-wide "interoperable" wideband public safety network at 700 
MHz based on cellular-style "4G" LTE technology.    Everyone in the field is 
going ga-ga over all the neat data services (database access, mapping, live 
video, extending office Ethernet LANs to the mobile, VOIP, etc) this will make 
possible,  but haven't begun to fathom the ASTRONOMICAL COST of building out 
the required  cellular-density  network (i.e. a base station every 5-10 miles 
or so) outside of the largest high-density urban areas.

While I was working at the L.A. County communications dept,  the major radio 
vendors (Motorola, the company formerly known as GE, etc) would come and give 
dog-and-pony-shows to the communications dept bragging about all the wonderful 
new features digital radio networks could offer the county public safety 
establishments.     I would always bring up this issue of "how much more base 
station infrastructure (i.e. sites) would this require?".   They would always 
squirm and immediately try to change the topic.......
_____________________________________________________________________________


--

Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
Home Page:          http://wa8lmf.net


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