On Thu, 01 May 2008 09:05:08 -0500, msg <msg@_cybertheque.org_> wrote:>Jeff Liebermann wrote: > ><snip> > >>>Now that we have digital radio, what seems to be >>>called HD radio (radio stations seem to advertise it pretty often). >>>http://en.wikipedia.org/wiki/HD_Radio >> >> >> Yep. It's the new name for Ibiquity (IBOC) radio: >> <http://www.ibiquity.com> >> I've played with commercial products. It's nifty. Good quality >> stereo crammed into a 9KHz AM broadcast channel. > ><snip>>Think twice about promoting IBOC; anyone who values the AM BCB spectrum >and the ability to hear low power, adjacent channel and DX AM radio >should loudly object to this fiasco. > >MichaelAh yes. After technology comes the politics. I'll resist jumping in with both feet. Incidentaly, the HD in HD Radio is "hybrid digital" not "high definition" (or "heavy duty). Marketing at work. <http://en.wikipedia.org/wiki/Hd_radio> It's an old axiom, that you don't get something new, without losing some of the old. In this case, you get hi-fi, low noise, better frequency response, 2 or more audio channels, data, realtime traffic updates, additional services, and possibly profitability for AM stations. What you lose is some legacy AM compatibility and increased adjacent channel garbage along with the usual added complexity. In my never humble opinion, it's a reasonable trade. While I got my start in radio listening to DX stations on my parents Grundig radio, I would personally be willing to lose some of that, in favor of technical progress and a radical improvement in performance and features. Note that in hybrid mode, as commonly used by US AM BCB stations, the digital portion of the xmit power is only about 1% of the total xmitted station power, where most of the power is also in the adjacent channels. There isn't going to be much 2nd adjacent channel (also known as alternate channel) splatter from that low power level. It's kinda academic because few AM receivers have the IF selectivity necessary to reject the adjacent channels anyway. However, the adjacent 9KHz channels will certainly be polluted. From a recent FCC report: <http://www.fcc.gov/mb/audio/digital/> <http://www.fcc.gov/fcc-bin/audio/FCC-07-33A1.pdf> According to McLarnon, the hybrid IBOC AM system creates two new "stations" in the first adjacent channels, each with a total power of -16 dBc. He states that for a 50 kW station, each would therefore be 1250 watts and current allocation rules provide protection of +6 dB D/U for first adjacent channels. According to McLarnon, if a station currently at +6 dBD/U adds IBOC, it creates a new source of cochannel interference to first adjacent channels at +22dB D/U. He believes that this is significant since it is 4 dB more interference power than is permitted by the Commission�s allocation rules for co-channel stations. McLarnon further states that the majority of existing allocations were created when first adjacent protection was only 0 dB D/U, and this figure still applies to the Canada-US bilateral agreement on AM broadcasting. I do have some not very nice things to say about the FCC endorsing a proprietary technology, from a single vendor (formerly Lucent), and other administrative oddities. Also, the FCC ignored European Eureka 147 technology: <http://www.worlddab.org> and went it's own non-compatible way. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Disadvantages of using AM for DSSS/FHSS?
Started by ●April 28, 2008
Reply by ●May 1, 20082008-05-01
