wrote in message
oups.com...
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.

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

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.
--
Drop the alphabet for email

"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

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.
--
Drop the alphabet for email

Well, Ari, I can tell you this. People used to mock the fact that I had 7
antennas on my 1957 station wagon almost 50 years ago, but these days, the
airwaves are so bereft of anything worth listening to, I never turn on a
radio in the car. So, I will never hear your message no matter what you
try.

Now, having said that, here is how the system design needs to be:
Since the frequency to which a target radio is tuned is an unknown, and
since the input contains a good trap for the IF frequency, your transmitter
needs to radiate about 2 KW ERP at each of three frequencies in the
broadcast band separated by 262 kHz and 455 kHz. This will mix in the front
end and produce a useful IF. Same technique on FM using two frequencies
10.7 MHz apart.

Good luck on the AM. With expected antenna efficiencies at that wavelength
of about 3%, you are going to need over 100 kW of RF and antenna components
with equivalent power ratings.

Let us know how it works out. The place I used to work no bid this about 20
years ago due to these problems, and that was not the first time this crazy
idea surfaced.

--
Crazy George
"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.
--
Drop the alphabet for email

On Sun, 2 Oct 2005 22:26:11 -0500, Crazy George wrote:

Well, Ari, I can tell you this. People used to mock the fact that I had 7
antennas on my 1957 station wagon almost 50 years ago, but these days, the
airwaves are so bereft of anything worth listening to, I never turn on a
radio in the car. So, I will never hear your message no matter what you
try.

Not even in an obvious disaster situation?

Now, having said that, here is how the system design needs to be:
Since the frequency to which a target radio is tuned is an unknown, and
since the input contains a good trap for the IF frequency, your transmitter
needs to radiate about 2 KW ERP at each of three frequencies in the
broadcast band separated by 262 kHz and 455 kHz. This will mix in the front
end and produce a useful IF. Same technique on FM using two frequencies
10.7 MHz apart.

Got it, thanks for the specs.

Good luck on the AM. With expected antenna efficiencies at that wavelength
of about 3%, you are going to need over 100 kW of RF and antenna components
with equivalent power ratings.

Yep, at least, maybe more but power availability off the emergency vehicle
is supposed to be a non-issue, we will see.

Let us know how it works out. The place I used to work no bid this about 20
years ago due to these problems, and that was not the first time this crazy
idea surfaced.

Do you think it is crazy from the standpoint of legal or technical. The
system itself would appear to be much needed.
--
Drop the alphabet for email

On Sun, 2 Oct 2005 18:29:13 -0400, Ari Silversteinn
wrote:

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.

Hi Ari,

As you have described it, and have seen the discussion in regard to
the need for ERP - you are so deep in the debit column with AM power
EQUAL to a local broadcaster, that to climb out of that hole would be
prohibitive. READ: no fire truck has a power plant sufficient to
cover both the antenna system losses AND "overbroadcast" as you
desire. And this is for ONE station only. Imagine your broader
mandate to "overbroadcast" all local stations and that hole just gets
deeper.

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?

With such a plea, to the savvy it reveals you are in over your head.

73's
Richard Clark, KB7QHC

On Sun, 2 Oct 2005 18:29:13 -0400, Ari Silversteinn
wrote:

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.

On Mon, 03 Oct 2005 10:05:07 -0700, Richard Clark wrote:

Hi Ari,

As you have described it, and have seen the discussion in regard to
the need for ERP - you are so deep in the debit column with AM power
EQUAL to a local broadcaster, that to climb out of that hole would be
prohibitive. READ: no fire truck has a power plant sufficient to
cover both the antenna system losses AND "overbroadcast" as you
desire. And this is for ONE station only. Imagine your broader
mandate to "overbroadcast" all local stations and that hole just gets
deeper.

OK, so we supply the amplification.

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?

With such a plea, to the savvy it reveals you are in over your head.

73's
Richard Clark, KB7QHC

Doesn't matter if I'm in over my head, the technical side is one I only
need to be able to commo on, there will be others who will be cast with
this task.
--
Drop the alphabet for email

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?

Doesn't matter if I'm in over my head, the technical side is one I only
need to be able to commo on, there will be others who will be cast with
this task.

How many leaps of imagination will it take to land on the gravy train?

73's
Richard Clark, KB7QHC

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.

--
Drop the alphabet for email