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Emergency Messaging And AM
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 |
"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. -- 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? 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 |
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. 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. Ari Silversteinn wrote: Crossposted to: rec.radio.amateur.antenna,rec.radio.amateur.misc, rec,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. -- Joe Leikhim K4SAT "The RFI-EMI-GUY" The Lost Deep Thoughts By: Jack Handey Before a mad scientist goes mad, there's probably a time when he's only partially mad. And this is the time when he's going to throw his best parties. |
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) 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. 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... 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. 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 Ari Silversteinn wrote: 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. |
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. |
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 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? -- Drop the alphabet for email |
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. -- Drop the alphabet for email |
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? -- Drop the alphabet for email |
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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. -- Drop the alphabet for email |
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? -- Drop the alphabet for email |
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 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 |
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 |
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. On Mon, 03 Oct 2005 11:50:35 -0500, Bob Bob wrote: I apologise if you already know the following! Its pretty basic radio.. Man, don't apologize, I have this semi-advanced understanding that missed a lot of the basics, if you get the drift. Thanks. 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. Got that. 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! lol ok 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 know 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! Now this I did not know! 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. Got it. 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. On Mon, 03 Oct 2005 11:50:35 -0500, Bob Bob wrote: 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. Found the expertise for that and there is a chunk of open source stuff out there, freeware. Being in a tunnel of course there werent really any licensing issues. Is that peculiar to Aus? On Mon, 03 Oct 2005 11:50:35 -0500, Bob Bob wrote: 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 Thanks, Bob, I'm all overYagied and underfractalled. lol -- 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. 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, 03 Oct 2005 13:37:49 -0500, Ben Jackson wrote:
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. Are you saying that if I am attempting an overbroadcast on, say, 680 AM and the station is doing the same, and I am 12 db + greater, that all we will get is squeal? -- Drop the alphabet for email |
Ari Silversteinn wrote:
Are you saying that if I am attempting an overbroadcast on, say, 680 AM and the station is doing the same, and I am 12 db + greater, that all we will get is squeal? One signal is the Beat Frequency Oscillator. I am amazed that no one has thought of this perfect solution before. If Morse code were required for all driver's licenses, then all you have to do is furnish a CW carrier wave. The two signals would mix and the squeal would be Morse code which would carry the emergency information. -- 73, Cecil, http://www.qsl.net/w5dxp |
On Mon, 03 Oct 2005 20:53:17 GMT, Cecil Moore wrote:
Ari Silversteinn wrote: Are you saying that if I am attempting an overbroadcast on, say, 680 AM and the station is doing the same, and I am 12 db + greater, that all we will get is squeal? One signal is the Beat Frequency Oscillator. I am amazed that no one has thought of this perfect solution before. If Morse code were required for all driver's licenses, then all you have to do is furnish a CW carrier wave. The two signals would mix and the squeal would be Morse code which would carry the emergency information. What if your fat as a whale and your DL is wedged up your crack in your back pocket? -- 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 |
"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. -- Drop the alphabet for email 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?? 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. |
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. "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. -- Drop the alphabet for email |
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. |
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 |
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. -- Drop the alphabet for email |
"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. -- Drop the alphabet for email 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. -- Drop the alphabet for email |
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. -- Drop the alphabet for email |
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 |
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 |
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. -- 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 |
"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 |
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