<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<meta name="Generator" content="Microsoft Word 14 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";
mso-fareast-language:EN-US;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
span.EstiloCorreioElectrnico17
{mso-style-type:personal-compose;
font-family:"Calibri","sans-serif";
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri","sans-serif";
mso-fareast-language:EN-US;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:70.85pt 3.0cm 70.85pt 3.0cm;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="PT" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal"><span lang="EN-US">Hi Darren,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">(Changed the subject line to match content better)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">>as usual, you raise a very interesting point: Range (reference to OM access to a repeater 100 km away).
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> Tetra is not exactly ideal for "typical" amateur usage because in TMO (repeater) mode, there is a 58 km absolute limit to
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> transmission range (in common with the TDM range limits in GSM). This range limit can be slightly extended (83 km) for<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> special services such as Tetra communication from helicopters (AGA mode) but the limits are hard coded within the
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> specification.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> Given that /\/\otorola digital is TDM based technology (2 time slots per carrier), does anyone know if there is a hard coded
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> limit on (base to mobile) transmission range?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> During enhanced conditions I have worked over 320 km (200 miles) with D-STAR on UHF from my car, it would be a
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">> shame to lose the ability to work DX by moving to other digital technologies that weren't designed for ham radio use.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">After doing some searching on what you mentioned, I found two interesting document both compairing DMR (ETSI TS 102 361) with TETRA; which do have some nice conclussion which also apply to D-STAR.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">- http://www.rrmediagroup.com/onlyonline.cfm?OnlyOnlineID=174<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">- http://www.zs6ro.co.za/files/documents/DMR/DMR_vs_TETRA_comparison.pdf<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">(especially the part "Coverage vs. Traffic")<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Some conclussions which are also interesting for D-STAR seams to be:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">- D-STAR (like DMR) has a relative simple modulation sceme (DMR uses 4FSK, D-STAR uses GMSK). This is less demanding on the linearity of the amplifier then TETRA which then has a number of concequences:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">-> simpeler tranceiver design and the ability to use analog FM-transceiver (as used by all D-STAR homebrew projects)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">-> because of that, easier to design high power transceivers (which is good for range).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">It should be noted that this easier modulation sceme is a trade-off which results in a lower "bit/Hz" ratio and therefor less capacity per spectrum.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">TETRA is designed to handle high demands of capactity in a small concentrated area (say a large fire in an urban area). D-STAR would simply not be able to handle this kind of situation.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">- The importance for VHF for long distance. TETRA is UHF only (althou the specification do support 100 Mhz to 999 Mhz). The ability to use 2 meter for D-STAR is a good point for range.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">As with the different homebrew projects for D-STAR, we are no longer dependent on i-com for radio and is now possible to move D-STAR down to 70, 50 or even 29 Mhz. It might be interesting to see how far D-STAR range can
be extended this way, especially for "mobile" use in rural areas.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">- Also, as you mention. D-STAR (unlike both DMR and TETRA) is a single-user-per-channel system. Having multiple users on the same channel (TDMA) imposses constrains on timing, and therefor distance. D-STAR does not have
this problem.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">It would indeed be sad to lose the ability to catch a rare "DX-contact" on digital voice too!<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">However, before we start getting to victorious saying "D-STAR is perfect for us", there DO still are other technologies out there that might be interesting to have a look at.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">On of them is dMPR (ETSI TS 102 490 / TS 102 658) that Trevor already mentioned in this list. It is also a FDMA system (like D-STAR), but with slightly different modulation parameters:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">- C4FM (4FSK) modulation: 2 bits / symbol<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">- channel width of 6.25 Khz (actually, more around 4 to 5 Khz), vs. about 7 to 8 in reality for D-STAR.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">It would be interesting to do some experiment with this, e.g. run D-STAR on top of C4FM in a 6.25 channel.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">- What is the impact of range? (smaller channel width would reduce noise, 2 bits / symbol modulation would need higher SNR ratio to demodulate).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">- Can it run on 29 Mhz (where the smaller channel-width with would be a big advantage)?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">- Can it be implemented and still maintain backwards compatibity for the existing infrastructure (e.g. use it only on 1.5, 4, 6 or 10 meter where all equipement is homebrew anyway, use it only on repeaters for repeater
input, ...)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">So, sofar my conclussion is, at first sight, D-STAR is actually doing a pretty good job as a ham system and does have a number of big advantages over TETRA; simply because the latter has been designed for a completely
different enviroment. <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">TETRA does not work in the more exotic ham enviroments (like long distance communication. D-STAR would not work well in the high-capacity high-usage enviroments which are more typical for emergency situations.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">But, this does not mean that it is not interesting to look what else is out there; learn from it, experiment with it; especially in the systems that do have open specifications and are possible to do in homebrew projects.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal">73 de Darren<o:p></o:p></p>
<p class="MsoNormal">G7LWT<o:p></o:p></p>
<p class="MsoNormal">73<o:p></o:p></p>
<p class="MsoNormal">Kristoff - ON1ARF<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</body>
</html>