On Sun, 02 Oct 2005 23:42:16 GMT, **THE-RFI-EMI-GUY** wrote:

A disadvantage I see is that a waiver is going to be required in order
not to violate FCC rules. In fact, in the state of Florida, interfering
with broadcast stations is against state law, so another hurdle to be
overcome.

Yes, the budget is rich with expected legal expenses. Since DHS has become
a player in this, we are hopeful that we can get the necessary punch to
overcome FCC and statutory issues.

That being said, for this system to work, you have to blanket
the entire AM and FM broadcast bands. Even doing so will leave out the
motorists who use XM or Sirius, the Ipod listeners and those who are
driving with their cellphones plugged into their ears.

Do we have to blanket or only blanket each locale, that is, the
broadcasting stations of each locale?

Not only will we miss those no AM/FM listeners, we will miss those that
don't have their radios on. An aggressive, road sign campaign is planned
something like " Turn On Your Radio, It Could Save Your Life" type of thing
near each incident site.

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On Sun, 02 Oct 2005 19:46:56 -0500, Bob Bob wrote:

Hi Ari

Thanks for comments, Bob.

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...

I'm missing your point. Please explain.

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)

Agreed.

Since part of your engineering exercise will be to determine what ERP
you want from the system you are proposing, the size of the antenna only
needs to be considered in line with the transmitter output power.
Obviously there will be a useful compromise somewhere that is cost
effective. You might for example want a 100 watt TX for each frequency
with a fairly lossy/terminated and loaded antenna. Your first port of
call will be to determine what the likely highest strength of an AM/FM
broadcast signal you will need to override, add maybe 20dB to that and
work out your needed ERP.

Good advice here, will 20db do it?

You will find lots of texts about the
inefficiencies of MF antennas mounted on motor vehicles so that will
give you some numbers to work with. Remember that making the antenna
wideband will also introduce substantial loss. Note that you cant design
the system to always work as you'll have situations where the radio
stations transmitting antenna is right next to then freeqy where the
event occurred! Decide on some statistical coverage percentage thing etc
etc...

Yes, we are shooting for max overbroadcasting but the reality is it is a
hit and miss proposition. Even the scenario of geo related obstructions is
a possibility.

I worked for a concern in Sydney Australia that put in tunnel
rebroadcast systems in the major underground roadworks in Sydney,
Melbourne and Perth. Being in a tunnel of course there werent really any
licensing issues.

Is that peculiar to Aus?

The system consisted of not only broadcast band (AM &
FM) receivers but spot VHF/UHF FM receivers and transmitters for police,
fire etc vehicles. Each broadcast frequency had its own transmitter. It
was thought to be a better idea than using a wide band TX covering all
frequencies. AM broadcast was coupled to a very long wire and the rest
used a terminated leaky coax run.

Cheers Bob W5/VK2YQA

Very nice, congrats on that. Was it Yagi technology or fractal?
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On 2 Oct 2005 18:36:56 -0700, wrote:

I agree Bob. "Tunnel Radio" systems have been around for over 20
years, and AFAIK all broadcast on dual IF frequencies covering both am
and fm car radios. Here in Boston this type of system is in use in all
our tunnels.

Harry C.

Harry, is this a "pickup" system for lost signal?
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On Sun, 02 Oct 2005 20:49:50 -0400, J. Teske wrote:

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.

And what makes you think anyone is going to be listening on AM. I
think the vast majority of radio listenings in urban areas listen to
FM except possibly for drive time shows, 24 hour news stations and the
comparatively few people enamored of talk or religious radio. FM of
course is subject to the capture effect wherein the strongest signal
prevails to the exclusion of others (at least that is the theory).

AM, particularly at night is subject to strong skywaves.

We are making no preference as to AM or FM as in that we will be attempting
to overbroadcast on each. The AM skywave issue is exactly that but the
system need not be perfect, only as perfect as possible.

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.

The 3 meter limitation is clearly is a problem here, we haven't modeled a 3
meter yet. I also wonder what, if anything, LFAM gets us in terms of FCC
approvals and state regulations.

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?

I think the problem here is not the technology, but a fundamental
misconception of what it is you are trying to prove and who is likely
to be your audience. At this point you do not need an engineer, you
need a sociologist.

W3JT

A sociologist?
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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.
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On Sun, 2 Oct 2005 23:02:15 -0500, Richard Harrison wrote:

Ari wrote:
"--amessaging system that would reach out approximately 1 mile--."

You don`t need a radio tire truck. You need a SOUND TRUCK with an AIR
HORN to get the audience`s attention to listen to the message.

Best regards, Richard Harrison, KB5WZI

I have seen these systems and they have failed to do two things.

Be heard in a modern car with loud radio and great insulation and 2) pass
the populace acceptance test.
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On Mon, 03 Oct 2005 08:22:17 GMT, G L Carter wrote:

Amen to that Richard.
I also question the wisdom of transmitting RF in a hazardous chemical
spillage area.

GeoffC

That is not on our side of the table though. How this sytem is ultimately
used is out of our hands.
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In that case, simply modify the sign to "Tune to 560, it could save your
life" and use a discrete frequency low power transmitter.


"Ari Silversteinn" wrote in message
.. .
On Sun, 02 Oct 2005 23:42:16 GMT, **THE-RFI-EMI-GUY** wrote:

Not only will we miss those no AM/FM listeners, we will miss those that
don't have their radios on. An aggressive, road sign campaign is planned
something like " Turn On Your Radio, It Could Save Your Life" type of
thing
near each incident site.

there is no requirement that anyone listen to any broadcast radio. with the
rapid growth of satellite radio there are even less people listening to
either am of fm broadcast radio. add those who listen to cd's or dvd's and
you get even less.

There are systems that are used for local road emergency notification, the
560khz one comes to mind, something along those lines would be the best bet,
and add in signs on the backs of vehicles. i guess the real question is,
what are you trying to do by overriding local broadcast stations? and over
what size area?


"Ari Silversteinn" wrote in message
...
On Mon, 3 Oct 2005 11:59:58 +1300, Ken Taylor wrote:

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.
--
The things that pop into my mind are why AM rather than FM, which tends
to
be more local, and do you intend to 'over-broadcast' only the local
channels
(how many?) - I assume you intend to make the channel(s) selectable - or
the
entire band to ensure you get everyone?

The issue of selective vs full range broadcasting is a matter that has not
been decided either by client, company or possibility. There are plusses
and minus' to each.

Selective would entail less power but we are being told power of the fire
engine is not an issue.

Assuming that there is a commercial
AM broadcast station in the vicinity (what, 10 miles? 20 miles?) you are
probably going to be flat out getting a mobile rig to ride over it. How
do
you intend to do this?

Cheers.

Ken

lol Good question, Ken. Any suggestions?
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On Mon, 3 Oct 2005 11:52:49 -0400, Ari Silversteinn


I think the problem here is not the technology, but a fundamental
misconception of what it is you are trying to prove and who is likely
to be your audience. At this point you do not need an engineer, you
need a sociologist.

W3JT

A sociologist?

Yeah, to figure out what has to be done to get the audience to listen
to you. A psychologist might also work.