[opendtv] Re: F.C.C. Likely to Open Airwaves to Wireless
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 16 Sep 2010 18:58:52 -0500
Craig Birkmaier wrote:
> Not exactly. As I understand it use of a UHF taboo channel causes
> inter-modulation products that can affect a range of non adjacent
> channels. This site describes the issues with UHF channel 30, for
> which there were 18 taboo channels for various reasons.
http://home.earthlink.net/~wb9nme/articles/atsc-5.html
Interesting site.
But, for example, in the DC market we do have a Channel 30, and we also have
(or soon will have, in few cases) 15, 25, 27, 28, 32, 33, 34, 35, 36, 38, and
39, all of which would have been tabboo according to that web site.
> John is correct that with DTV there are fewer UHF taboo channels,
> but there are more UHF channels used now, packed in less spectrum.
> So I'm not certain how much white space spectrum is available
> today versus during the NTSC era.
My bet is that the digital receivers are more immune to certain types of
interference, and of course the UHF tuners are more selective than the early
analog ones. For example, the interference inside the receiver needs to get
past the ~15 dB margin in order to bother the digital receiver at all, where in
analog sets, perhaps you could see impairment before then. That 15 dB margin
was also something Charles Rhodes mentioned, with respect to IM3 distortion. If
it's less than that, the receiver doesn't mind.
However, I did read in some FCC document that they were expecting white space
usage to perhaps be more valuable in rural settings, where the long range may
facilitate wireless broadband provisioning, and where more white spaces would
exist. Because I would agree that there aren't so many white spaces in large
metro markets now.
Bert
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