Doug Smith W9WI wrote:
On Thu, 24 Jul 2008 14:41:36 -0400, Steve Bonine wrote:

There's an article in today's Washington Post

http://preview.tinyurl.com/6ego68

I had to chuckle at the part where she holds the camera on herself at
arms length. High budget reportage.

I also was in awe of the publc safety aspect touted by the one engineer.
First responders, yada yada. Of course they could use it.

The manager who is talking about having a product out in less than a
year, after tehy know what the "rules" are.

Finally the last guy in the red shirt who basically says that what they
have doesn't work.

Golly, if it doesn't have to work, I could have something on the market
in a week or so evil grin


I'm not too worried about interference to/from amateur radio.

This isn't too likely to interfere with Amateur radio. Of course, I
don't think it is too likely to work either. Given the nature of UHF,
the system will have to look at the possible occupation of a frequency
at both the broadcast site and receiver site. Picket fencing can be an
issue. Let's take a look at a potential experience.

The home system (digital signal source) and receiver system (laptop)
look around for a clear space. Say they find one. I am guessing that
there is some sort of Pre-communication going on on some dedicated
frequency. So they find a clear frequency. They start exchanging
packets. Now the laptop moves and a picketed signal shows up, or say the
local church starts it's Saturday evening service. So now the home
system and the receiver system have to search around for a new
frequency. Maybe they find one, and maybe they don't.

Immediate thoughts come to mind:

These systems have to be in some kind of communication to begin with. I
suppose that the laptop could just start transmitting on different
frequencies, hoping to hit the home system, but that would be a long
process.

Talk about a system ripe for interference. There could be a new game in
town, the opposite of Wardriving. If all it takes is another signal on
the same frequency to start a search for a clear one, some social
misfits might just have fun with a sweep generator. Keep the system
hopping, and it will never settle on a frequency.


snippage


I'm a lot more worried about it as a TV engineer and semi-rural
over-the-air TV viewer. In early tests these things weren't very good at
determining whether a channel was unused. I can see that becoming a big
problem in semi-rural areas like this, where people might be using rooftop
antennas to get TV but the Internet devices will probably be on makeshift
indoor aerials.

Is is possible that this is another setup put together by digital
engineers as opposed to RF engineers?

So I agree with Steve that it is likely to be another BPL. This one
might get a little further before failure though, as I think ARRL's
efforts went a long way toward getting BPL marginalized. Obviously we
won't be spending our money on a problem that won't directly affect
Hams. But it has th esame problems, likely interference, lack of
robustness, and probably won't help th epeople touted as the beneficiaries.

Just my .$0.02

- 73 de Mike N3LI -