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...


I'm missing your point. Please explain.

I apologise if you already know the following! Its pretty basic radio..

Almost every radio receiver on the market works off the "superhetrodyne"
principal where the incoming signal is mixed with a local oscillator
down to an intermediate frequency. This makes receiver design a little
cheaper as you can then put your expensive filtering at one frequency
rather than have something that has to track the actual transmitted
frequency.

For example a station on the AM band at 870khz is mixed with a local
oscillator of 1325 khz (in the receiver) to get a difference of 455khz.
If the station frequency is changed then one only needs to modify the
local oscillator frequency. This is what the knob on the radio does!

The most common IF frequency for an AM radio happens to be 455khz so
transmitting on that will mean you will be heard on all AM radios in
close proximity. I dont off hand know the most common broadcast FM IF
(maybe 10.7MHz or 7.8Mhz) but that should be easy to find. It is
important to make sure that the IF of the fire trucks FM two-way radio
isnt the same or you'll never be able to hear it inside the truck!

To "broadcast over" you would need to amplitude modulate the AM band
455khz TX and frequency modulate the FM broadcast IF frequency.

Good advice here, will 20db do it?

FM is easier to do than AM. I'd factor in maybe 6dB for FM. You might be
able to get by with 12dB for AM but the original station will make some
small amount of noise under it. The important thing is that the person
listening wil be able to understand the content.

Note that this is of course only relevent when transmitting on the
actual station frequency.

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.

Well it shouldnt be that hard to model. Do a AM and FM band coverage
prediction over the freeways etc you are doing the experiment on to
discover what the receive strength will be in dBm. (It doesnt matter
what "gain" you make the RX antenna because it will be the same figure
that is used for your overbroadcast) For every say 200 yard square take
the mean signal of each, then take the 80th percentile as the signal you
have to beat. If that was (say) -80dBm you want -74dBm (for FM) at the
maximum operating distance (was it a mile each way?) You then reverse
model that to determine what the TX EIRP of the thing on the truck has
to be.

There are bound to be contract houses that will do this prediction for
you. I use to work for one that had the software and I have some GPL
versions myself. I cant do MF (ie AM broadcast) though.

Being in a tunnel of course there werent really any
licensing issues.

Is that peculiar to Aus?

The licensing issue or the tunnel? Tunnel rebroadcast is pretty common
around the world. The company I worked for also did one in Indonesia.
Its also used in underground mines.

Very nice, congrats on that. Was it Yagi technology or fractal?

Err, the leaky coax was just a 2km run of an Andrews product that has
leaky holes in the shield. It was fed in the middle with a wide band
splitter and terminated with 50 ohmss at each end. Its quite a common
thing to do in underground environments. (Buildings too) Handy for two
way radio as well as cell phones.

The AM thing was just a very long terminated (600r) wire.

None of the above are yagi or fractal

Cheers Bob


Ari Silversteinn wrote:

On Mon, 3 Oct 2005 11:57:50 -0400, Ari Silversteinn
wrote:
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.
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.

And you've offered this is during an obvious emergency? :
1 Why would they play music loudly in an insulated car when doom is
on their heels?
2 Why would neighbors complain of noise telling them they were about
to be die?

Richard's description adequately suits:
Local - that would reach out approximately 1 mile and "overbroadcast"
to those immediately in danger within a stationary site.

Your objections are more tailored to suit your solution than the
problem.

73's
Richard Clark, KB7QHC

On Mon, 3 Oct 2005 11:28:32 -0400, Ari Silversteinn
wrote:

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.

While Florida may have laws to this effect, in fact they are
unenforcable because of federal preemption for all radio matters.
Still illegal, just the wrong enforcement entity. A state or locality
cannot for example legislate on TVI matters (though many have tried.)
When they try, the FCC will send a notice to the locals that they are
in charge and will handle enforcement. Unfortunately the FCC is
unwilling to get involved in the matter of private contracts such as
antenna exclusions in housing developments.

That said, be aware that when it comes to radio useage in the US, the
FCC is actually NOT the ultimate authority. They are responsible only
for those frequencies which a military controlled panel has ceded to
the FCC for administrative purposes. I can't remember the name right
off hand, but during my federal career, I had to work with them and we
actually were able to override an FCC allocation because it interfered
with a military application. While the FCC played ball with the DOD
outfit I worked for, the ultimate beneficiary of that allocation (a TV
station) sued and the matter wound up in Federal Court. The court
reaffirmed the DOD's ultimate sovreignity in this matter. It
ultimately got resolved by some allocation juggling when a combination
of the Court, The FCC and the DOD gave the plaintiff some "religion."

W3JT

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 Mon, 3 Oct 2005 11:28:32 -0400, Ari Silversteinn
wrote:

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.

Hi Ari,

The various pieces of this jigsaw puzzle is beginning to reveal a
picture here. With the introduction of two governmental
organizations, and their regulations, your "plan" has all the
appearances of being suitably crafted to work on paper. It responds
to the individual issues that any squinty-eyed bureaucrat would demand
be satisfied for his postage sized turf, but in the overall it would
fail miserably, or drive costs so high as to be tainted with the plea
that "aren't people's lives worth the price?"

Let's see, the original spec calls for a disaster situation that is
confined to within 1 mile; that demands the local population be
informed; that over-rides their usual paths of communication; that
reaches them even when they are not engaged in listening.

As already pointed out, big sound trucks do wonders, and have worked
well since the beginning of the last century for this purpose. That
kids inside their home can hear the ice-cream truck a mile away is a
testimony to this simplicity.

Knocking on the door of the local broadcasters and commandeering their
air-time has a time honored tradition of working quite well too. This
involves no more time than getting that expensive mobile power plant
rigged with wide band transmitters working into hugely lossy antenna
systems into the same danger area. After-all, you could as easily
call the first most obvious radio station as them, and you could be
calling the others before they even got on the road.

The solution demanded is that all radio stations respond to a disaster
network alert and citizens tune to the Civil Defense frequency when so
warned by them. Is this another administration cut-back that was
shelved as one of those unnecessary "entitlements?" Have they clipped
all the wires to those old Air Raid sirens? When did the lights go
out in FEMA?

73's
Richard Clark, KB7QHC

On 2005-10-02, Ari Silversteinn wrote:
This would be an "overbroadcast" (my term)
in that it would override local AM radio broadcasting to reach into cars,

My experience with AM (on the aircraft band) is that two transmitters
at the same time yields a horrible squeal and nothing else. The louder
station (usually on the ground with hundreds of watts) has no particular
advantage over the other station (usually in the air with 5-10 watts).
In other words, there is no effect like FM capture.

--
Ben Jackson

http://www.ben.com/

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.
--
Drop the alphabet for email

On Mon, 3 Oct 2005 16:20:40 -0000, Dave wrote:

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.

The loss of listenership is not arguable.

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?

1) to grab those that are listening to AM/FM, it is still a hyooge market,
2) client request, 3) DHS preference 4) the number of people alerted by a
sign/sticker and independent warning channel is much less than both that
and AM/FM, 5) the possibility that once the AM/FM FCC/NAB bond is broken, a
precedent could be set for cell, sat, threading messaging, etc 6) spinoff
tech for local/reg/national emergencies.

and over
what size area?

1 mile radius max from point of incident, less most probably.
--
Drop the alphabet for email

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.

On Mon, 03 Oct 2005 12:58:40 -0400, J. Teske wrote:

While Florida may have laws to this effect, in fact they are
unenforcable because of federal preemption for all radio matters.
Still illegal, just the wrong enforcement entity. A state or locality
cannot for example legislate on TVI matters (though many have tried.)
When they try, the FCC will send a notice to the locals that they are
in charge and will handle enforcement. Unfortunately the FCC is
unwilling to get involved in the matter of private contracts such as
antenna exclusions in housing developments.

Is there a reason that the locals try to overwrite Fed law then?

That said, be aware that when it comes to radio useage in the US, the
FCC is actually NOT the ultimate authority. They are responsible only
for those frequencies which a military controlled panel has ceded to
the FCC for administrative purposes. I can't remember the name right
off hand, but during my federal career, I had to work with them and we
actually were able to override an FCC allocation because it interfered
with a military application. While the FCC played ball with the DOD
outfit I worked for, the ultimate beneficiary of that allocation (a TV
station) sued and the matter wound up in Federal Court. The court
reaffirmed the DOD's ultimate sovreignity in this matter. It
ultimately got resolved by some allocation juggling when a combination
of the Court, The FCC and the DOD gave the plaintiff some "religion."

W3JT

Excellent point, in my research I saw this handoff or spectrum management
authority of the DoD and it makes sense. This is a serious, additional
consideration and is all the more reason to get the DHS' blessings.

Thanks.
--
Drop the alphabet for email

On Mon, 3 Oct 2005 11:28:32 -0400, Ari Silversteinn
wrote:

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.

On Mon, 03 Oct 2005 10:27:09 -0700, Richard Clark wrote:

Hi Ari,

The various pieces of this jigsaw puzzle is beginning to reveal a
picture here. With the introduction of two governmental
organizations, and their regulations, your "plan" has all the
appearances of being suitably crafted to work on paper. It responds
to the individual issues that any squinty-eyed bureaucrat would demand
be satisfied for his postage sized turf, but in the overall it would
fail miserably, or drive costs so high as to be tainted with the plea
that "aren't people's lives worth the price?"

No one, in the end, will care about that, Richard, it's buzz words. The
economic hooks are in lessened liabilities and coordinating better
emergency evac and site control plans. Money talks here.

Let's see, the original spec calls for a disaster situation that is
confined to within 1 mile; that demands the local population be
informed; that over-rides their usual paths of communication; that
reaches them even when they are not engaged in listening.

As already pointed out, big sound trucks do wonders, and have worked
well since the beginning of the last century for this purpose. That
kids inside their home can hear the ice-cream truck a mile away is a
testimony to this simplicity.

That piece is a given, no argument there, the AM/FM piece is just one more
way to insure commo.

Knocking on the door of the local broadcasters and commandeering their
air-time has a time honored tradition of working quite well too. This
involves no more time than getting that expensive mobile power plant
rigged with wide band transmitters working into hugely lossy antenna
systems into the same danger area. After-all, you could as easily
call the first most obvious radio station as them, and you could be
calling the others before they even got on the road.

Yes, but as we recently saw, things left to the "if come" often don't
"come" ask FEMA. The plan needs to be in place and the control out of the
hands of anyone except local/reg/national authority.

The solution demanded is that all radio stations respond to a disaster
network alert and citizens tune to the Civil Defense frequency when so
warned by them.

Nothing wrong with that if you know where to tune. I don't, come to think
of it.

Is this another administration cut-back that was
shelved as one of those unnecessary "entitlements?" Have they clipped
all the wires to those old Air Raid sirens? When did the lights go
out in FEMA?

73's
Richard Clark, KB7QHC

MOF, it's an idea that came up over dinner during FEMA/NOLA, don't know
about the sirens, all I do know is once FEMA got there, they shutdown most
commo inc police in some cases. They want total control so this p[iece has
more play at the immediate response (local/state) levels.
--
Drop the alphabet for email