Suggestion: Why don't you also broadcast such "emergency" information over
the entire spectrum of wireless network frequencies? That way, you could
post the information into every Usenet group on the globe. Just like you
have done with these postings.

"Ari Silversteinn" wrote in message
...
Crossposted to:

rec.radio.amateur.antenna,rec.radio.amateur.misc,r ec,radio.amateur.equipment

Novitiate he

I am learning AM broadcast basics in particular the issues regarding the
geo-targeted broadcasting of alert messages from moving vehicles. Would
most appreciate any assistance.

Due to Katrina/Rita, the company I work for has been given the opportunity
to demonstrate a messaging system that would reach out approximately 1
mile
+/- in transmission deliverance. This would be an "overbroadcast" (my
term)
in that it would override local AM radio broadcasting to reach into cars,
trucks etc. In particular, we are working with a stationary site (a
chemical spill for instance) and an emergency vehicle that would move back
and forth at and through the site, at up to 70 mph, broadcasting an alert,
voice and tone message.

Reading about LPAM, this looks technically possible but one concern I have
is antennae size. A fire truck, for instance, could have an antenna
mounted
on its front, and up to 4 feet over the top of its roof, so we might look
at as much as 20 feet of length. I realize this places us over the 3 meter
max so one of the ???? is whether LFAM is realistic.

Am I way off base here, can any antennae, fractal or other, or any AM
antennae technology, be utilized to design an antenna and propagate this
type of signal?

All comments appreciated.
--
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"Ari Silversteinn" wrote in message
...
On Mon, 3 Oct 2005 12:01:14 -0400, Fred W4JLE wrote:

In that case, simply modify the sign to "Tune to 560, it could save your
life" and use a discrete frequency low power transmitter.

I assume you mean to take up an unused local channel? Or to bargain for
time on a used one?

Both ideas make sense.
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On Mon, 3 Oct 2005 21:47:29 -0000, Dave wrote:

if this is for real time notification you don't have time to bargain or to
find an unused channel... and who would listen to you anyway if it was
unused? how often do you turn the knob on your car radio??

Often actually and I agree about the unused channel, at first blush

what about the emergency broadcast system? that would seem to be the
'proper' method of emergency notification, its already set up for all sorts
of local, regional, and national notifications.

The EBS is voluntary, this is not.
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On Mon, 3 Oct 2005 17:58:33 -0400, Fred W4JLE wrote:

There are a couple of frequiencies for unlicensed low power am stations. You
can see them in use by real estate folks selling houses. There are no
commercial stations on the frequency.

Yes, and at Disney World, etc. This is a very doable idea and may well
solve FCC/DoD issues.
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Hi Ari

I always wonder whether broadcast at the most common IF frequencies
would be a viable alternative? (eg 455khz for AM) Legality issues aside
of course... This would make frequency selection a little easier to
engineer. You wouldnt have to divide your power budget into many
operating frequencies as well. Problem is that you'd need a lot higher
ERP especially since car mounted radios tend to be better shielded than
portables. (You'll need to experiment some)

On 3 Oct 2005 18:52:41 -0700, wrote:

Wonder no longer, because broadcasing at IF frequencies has been for
year the standard in the US. In spite of some rather silly speculative
posts, this mechanism has proved itself for more than 10-years here.

In a confined space such as a tunnel, a transmitter of 10-watts more
than sufficint to get the job done, and using nothing more
sophisticated than a simple wire radiator running the length of the
tunnel.

In Boston, we also retransmit commercial radio broadcasts into our
tunnels, but that requires equipment dedicated to each radio channel
that we re-broadcast, and that becomes very costly after 10 stations or
so, hence there is a limit.

The real challenge is in maintaining emergency communications to the
outside from within our tunnels. All are serviced by the traditional
leaky coax that runs along the top of the tunnel, but considering that
all of these emergency services operate on their own indepdendent
frequency bands, so servicing them simulteously becomes somwhat
problematic. particularly when hand-held, low power devices enter the
big picture.

Harry C.

Problematic? That would be an understatement.
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On Tue, 4 Oct 2005 14:57:01 +1300, Ken Taylor wrote:

All agreed, but that is in a tunnel, which has the advantage of not having
to overcome the still-received commercial stations. The OP wants to do this
out in the open, anywhere, any time. He also wanted to do it while driving
at high speed for some reason, but I think he's quietly shelved that part of
the idea.

Cheers.

Ken

MOF, it has reared its ugly hi speed head again.
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On Mon, 03 Oct 2005 14:31:36 -0700, Richard Clark wrote:

On Mon, 3 Oct 2005 16:33:52 -0400, Ari Silversteinn
wrote:
OK, so we supply the amplification.

OK, this is just a re-run of previous speculations. You don't know
the depth of your energy budget crisis, do you?

Open coffers.

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On Tue, 04 Oct 2005 14:54:42 GMT, Wayne P. Muckleroy wrote:

Suggestion: Why don't you also broadcast such "emergency" information over
the entire spectrum of wireless network frequencies? That way, you could
post the information into every Usenet group on the globe. Just like you
have done with these postings.

Usenet being a place that only a few people access, aside from that, it's
not a bad idea, actually.
--
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"Ari Silversteinn" wrote in message
...
On Tue, 4 Oct 2005 14:57:01 +1300, Ken Taylor wrote:

All agreed, but that is in a tunnel, which has the advantage of not
having
to overcome the still-received commercial stations. The OP wants to do
this
out in the open, anywhere, any time. He also wanted to do it while
driving
at high speed for some reason, but I think he's quietly shelved that part
of
the idea.

Cheers.

Ken

MOF, it has reared its ugly hi speed head again.
--
Sorry, what's 'MOF'?

Ken

"Ari Silversteinn" wrote in message
...
On Mon, 3 Oct 2005 17:58:33 -0400, Fred W4JLE wrote:

There are a couple of frequiencies for unlicensed low power am stations.
You
can see them in use by real estate folks selling houses. There are no
commercial stations on the frequency.

Yes, and at Disney World, etc. This is a very doable idea and may well
solve FCC/DoD issues.
--
When was the last time you listened to one of those frequencies? It won't
get the message out where it's needed.

Ken

"Ari Silversteinn" wrote in message
...
On Mon, 03 Oct 2005 14:31:36 -0700, Richard Clark wrote:

On Mon, 3 Oct 2005 16:33:52 -0400, Ari Silversteinn
wrote:
OK, so we supply the amplification.

OK, this is just a re-run of previous speculations. You don't know
the depth of your energy budget crisis, do you?

Open coffers.

--
He wasn't referring to your finance budget, but your energy budget. I
hesitate to say it can't be done in any practical sense, but that's my
thought. The idea of one poster to transmit on the IF's is a good one but I
didn't suggest that because you'll also kill your emergency services comm's.

Incidentally, do you plan to have every loco in the US fitted out or are you
going to fly the loco's to the incident site to do their stuff?

Cheers.

Ken