The Icom and Kenwood commercial systems use a different modulation system hence the narrower bandwidth.
The current modulation scheme for D-STAR is really designed for 10 kHz channel spacing, although it can just about be squeezed into 8.33 kHz channels. You cannot acheive 6.25 kHz channel spacing D-Star is a real world environment. The Icom/Kenwood PMR system uses the same Codec as D-Star with 3200 bps Voice and 1200 bps data but they don't use GMSK. Addition info is on ICOM-UK's website at http://www.icomuk.co.uk/categoryRender.asp?categoryID=3776 Perhaps the challenge for Amateurs is to developed a modulation scheme that can handle 3200/1200 Voice/Data and fit into 5 kHz or less channel spacing. 73 Trevor M5AKA ---- NXDN - Association of American Railroads (AAR) http://falconinfo.blogspot.com/2008/09/aar-chooses-nxdn-digital-standard.html --- On Fri, 2/10/09, John Hays <[email protected]> wrote: From: John Hays <[email protected]> Subject: Re: [DSTAR_DIGITAL] Re: ARRL Approves Study Committee to Research & Develop Plan for Narrowband Chan To: [email protected] Date: Friday, 2 October, 2009, 11:14 PM NXDN uses the same codec/modulation as D-STAR, that is why D-STAR DV is claimed to be 6.25 Khz., the radios may just not be as tight. I think the Utah VHF Society studies showed that different models of Icom D-STAR radios exhibited different RF characteristics. http://utahvhfs.org/dstar.html -- in figure 4 at http://utahvhfs.org/dstar_channel_spacing.html it says that two D-STAR signals of equal strength can co-exist at 6.25 Khz. spacing. On Oct 2, 2009, at 2:49 PM, Trevor . wrote: But commercial systems (NXDN) with mobiles, handhelds and repeaters that use 6.25 kHz channel spacing have been available for years - both Icom and Kenwood are active promoters of the system which uses a far more efficeint modulation techique that D-Star, see 2005 - Icom and Kenwood demo 'Very Narrowband Digital Communications Technology' http://www.southgat earc.org/ news/apr2005/ icom_kenwood_ demo.htm 2008 - The Gadget Show tests digital and analog walkie talkies http://www.southgat earc.org/ news/november200 8/gadget_ show_radio_ tests.htm 73 Trevor M5AKA .. John D. Hays Amateur Radio Station K7VE PO Box 1223 Edmonds, WA 98020-1223 VOIP/SIP: [email protected] Email: [email protected]
