[opendtv] Re: news: F.C.C. to Open Radio Spectrum

  • From: Albert Manfredi <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Wed, 5 Nov 2008 21:01:37 -0500

John Shutt wrote:
>> If you allow WSDs at 40 mW in adjacent channels, or
>> even N+/-2 and N+/-6 which have all proven vulnerable,
>> you need at least 55 dB of selectivity, worst case.
> So those rules can't be built into a WSD?
You mean, do not allow what the FCC is claiming they want to allow now? Yes, 
they could do that. They could certainly say that WSDs can't use channels 
unless they are, f'rinstance, least 3 channels away from the occupied channel.
So instead of making us go on "faith," why didn't the FCC do their homework 
first, BEFORE allowing these menaces to be perpetrated on us? I have to believe 
that there are real engineers at the FCC scratching their heads, wondering what 
on earth the lawyers are up to. Tell us the real rules, test them out, THEN see 
if these things make sense. As of now, they do not, by the FCC's own reports.
This is an especially difficult environment the FCC is trying to play in. 
Similar to allowing WSDs to work in the satellite or GPS bands, which is not 
something anyone would take on sort of on the spur of the moment. As they did 
here. This is nothing like the case of unlicensed devices sharing the WiFi 
> I fail to see how a 40 mW anything is going to provide
> much rural service. And if someone is providing rural
> internet service, they are pretty much working in a known
> location, with known licensed users, and will be known to
> the licensed users in case of interference.
First part of the answer: it's the disingenuous hype in the press, and the 
self-serving dramatics from some manufacturers or services, that keep 
mentioning broadband access. They do this to get public support for this idea. 
You know, mislead the innocent. Hey, who can be against broadband access, 
motherhood, and apple pie? And anyway, as you point out, this is hardly the 
difficult case. But the FCC is in fact allowing just about anything. Say, ad 
hoc nets for multiplayer games. To me, that's a very difficult case.
For fixed service, the power limit is 4 watts. And, of course, if someone 
really wants to provide broadband access in rural areas, they would probably go 
with two-way satellite (which is available) or with 802.16, which provides 20 
or 28 MHz wide channels.
The lower power levels are the difficult examples of WSDs. With geo-location, 
operating in a freq channel not adjacent to a TV channel, 100 mW. 
Auto-sensing-only, 50 mW. In adjacent channels to an occupied channel, 40 mW. I 
was using 40 mW to show that even it, the lowest allowable, is not low enough 
for adjacent or many other non-adjacent channels.
Check out A/74. Adjacent channel selectivity, when the TV station is not very 
strong, is only 33 dB. We would need 55 dB or better, with the rules as the FCC 
has set them.
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