Wireless Growth & Wireless Interference 132
windowpain writes "An article in Monday's Washington Post says "The explosive growth of the mobile phone industry has crowded and tangled the nation's airwaves to such an extent that wireless company signals are increasingly interfering with emergency radio frequencies used by police and firefighters, public safety agencies said." Wifi is not a problem, evidently. Understandable, given its short range."
How can this happen? (Score:4, Interesting)
=> fire people at FCC or sue mobile companies.
Re:How can this happen? (Score:5, Informative)
NEXTEL is the prime culprit. The problem stems from what NEXTEL is.
a NEXTEL phone appears to be a cell phone, but legally it is a handheld, trunked two-way radio with full-duplex capability and access to a phone patch. While this accurately describes a cell phone, the evolution differs.
"Cell phones" that follow the CDMA, GSM, TDMA or even AMPS (analog) standards are all using standards that were originally developed for use as telephones. They are licensed as telephones, and use portions of the spectrum that are reserved for telephones.
Cell phones that follow the iDEN standard (this would be NEXTEL) use a protocol that evolved from a half-duplex digital trunked two-way radio system.
What NEXTEL used to be in the business of (under a different name, which I can't recall at the moment) was providing nationwide fleets with trunked digital two-way radio service. Someone in NEXTEL had this brilliant idea that if you could add full-duplex capability and a massive banked phone patch that you could compete with the cellular companies, and this is what they did.
The problem with this is that NEXTEL, being an operator of a Commercial Land Mobile Radio Service (CLMRS), gets to license portions of the spectrum intended for Land Mobile Radio Service users.
...and there is the rub. Police, fire departments, ambulances, tow trucks, taxis, and just about every business except sometimes aviation and maritime businesses, are users of the Land Mobile Radio Service. Like NEXTEL, they license portions of the spectrum that are there for the Land Mobile Radio Service (there is no distinction in spectrum allocation between a commercial and a private LMRS license).
The biggest pain here is involved in that NEXTEL does not operate on the same frequencies everywhere. They go from location to location, licensing 5-20 frequencies in the 800MHz LMRS band (and I think sometimes in the 900MHz LMRS band) in any given location, but the frequency that they allocate in one city may be the same frequency that a police department in another adjacent city is using.
Yes, the FCC probably should have prevented this. However, their allocation scheme was good enough for systems that had a low duty cycle, and it worked for decades. Introduction of a high duty cycle system such as NEXTEL broke the system.
Incidentally, I strongly advocate that police, fire and other services should not move to 800MHz trunked systems if they don't have a serious need to. The fire department in my home town of Selkirk still uses the same frequency (46.06MHz) with no repeater, no trunking, nothing except for a remote base (which communicates to the three firehouses on 460.6375 and 455.6375MHz) and provides complete coverage for the fire district with minimal vulnerabilities, including immunity from interference from NEXTEL.
BTW, WiFi is not a problem because the frequencies are nowhere near 800MHz.
Understandable (Score:5, Insightful)
Correction (Score:4, Informative)
Actually, only 802.11b operates at 2.4 GHz. 802.11a operates at 5 GHz.
The emerging 802.11g standard is intended to deliver the same data rate as 802.11a but on the 2.4-GHz band.
Re:Correction (Score:2, Informative)
Re:Correction (Score:1)
Re:Correction (Score:3, Informative)
No kidding (Score:1)
And microwave ovens? (Score:1)
Interestingly, microwave ovens operate at 2.45 GHz (not listed on the spectrum allocation chart mentioned elsewhere). I wonder how effective the shielding of a typical microwave oven is. If they leak 1% (for example when loaded with a very small amount of food), then that's still 8 W, compared to 1 W for a GSM mobile at 1.8 GHz. I don't know either within what tolerance MW ovens are; for the food inside it doesn't matter very much whether it
Re:And microwave ovens? (Score:1)
That's it!! The moment my WiFi interrupts with my microwave, it's going out the window!!! How dare WiFi interrupt me cooking my Pizza Pockets!!
Re:And microwave ovens? (Score:1)
Re:And microwave ovens? (Score:2, Interesting)
Locally even worse... (Score:5, Informative)
Re:Locally even worse... (Score:2, Funny)
yeah but can't you guess why that is?
Re:Locally even worse... (Score:3, Insightful)
Re:Locally even worse... (Score:1)
Re:Locally even worse... (Score:1)
Frequency Encroachment (Score:4, Informative)
The basic argument, like the article makes for first responders, is that the military band for communications is being encroached upon by civilian use. Having fewer frequencies directly impacts the military's ability to conduct training operations and exercises.
The Navy (Department of Defense) [navy.mil] has a page which educates visitors and range spectrum users on how to defend against civilian encroachment of DoD frequency spectrum.
The Electromagnetic Spectrum Training Chart [navy.mil] shows military uses of certain frequencies and the competing civilian use.
Police chatter in the classroom (Score:5, Interesting)
This problem has been around for some time in the hearing [wired.com] impaired [gallaudet.edu] community.
Re:Police chatter in the classroom (Score:3, Interesting)
some obvious questions that (Score:5, Insightful)
- If spectrum is reshuffled, could this be an opportunity for the wifi-friendly (but still evil) Powell to allocate more unlicensed spectrum?
- Alternately, does the emergence of the interference bogeyman in such a prominent publication imply a tough PR road for more free spectrum?
- Could this be an opportunity for the cell carriers operating in the 800MHz band to switch to different technologies, or roll out newer services?
- Could these sorts of problems be used to get some federal money thrown toward development of software radio? would multi-format devices help avoid this problem?
As the submitter mentions, these emergency bands don't appear to be abutting or affecting the 2.4GHz range, but I imagine these issues will be relevant as wifi expands and interference problems begin cropping up.wifi = different spectrum, limited deployment (Score:3, Insightful)
Exactly how crowded? (Score:3, Interesting)
There are several wireless companies operating in the 800 megahertz band...
How finely split can the spectrum be before there's danger of overlap? Is it possible for, say, one phone to send signals at 800.0001 MHz while another does so at 800.0002 MHz? Where is the precision cutoff for neighboring frequencies before things start to interfere?
Re:Exactly how crowded? (Score:4, Informative)
Of course (Score:2)
Re:Of course (Score:1)
You'll need both (Score:4, Informative)
I really don't know about that. Just as receivers have tolerances, transmitters do too. So if I have a crappy transmitter and I tell it to broadcast at a certain frequency, there will be a certain tolerance there, unless I'm using a laser. They're certainly not. Even with a good transmitter, there's a certain +/- to the frequency distribution, although presumably less.
So ultimately, his question was quite a fair one - for someone to tell the difference between two signals 800.0000001 and 800.0000002, the two transmitters will have to be good enough to send out precise, narrow signals, and his receiver will have to be good enough to tell the difference.
Re:You'll need both (Score:1)
Re:You'll need both (Score:3, Funny)
Well, assuming they spend more on the transmitter than you do on your cell phone, huh? ;) Although the way Sprint's been lately, I'm not so sure.
Re:You'll need both (Score:3, Informative)
Re:You'll need both (Score:2)
I'm so sad I actually look forward to getting called on things like that these days. Yes, of course you're correct, particularly if said laser isn't operating through a vacuum. Compared to an analog transmitter, however...
Re:You'll need both (Score:5, Informative)
A radio signal, unless it's a pure sine wave, uses a certain amount of bandwidth. Double the amount of data pushed through, and you double the bandwidth used, all other things being equal.
For example, my R/C plane uses 72.450 mhz, and the bandwidth used is 20 khz, so 72.441 mhz -> 72.459 mhz are what's in use. Well, that's what's allocated anyways -- the radio should use a little less. The transmitter should not transmit signifigant amounts of power outside of that range, and the receiver should ignore any signals outside of that range.
(For comparison, morse code can use less than one khz of bandwidth. FM voice transmissions (such as used by police radios) take up 3-6 khz. SSB and FM use less, but the sound quality is less too. More bandwidth = more quality, though certain modulation types work better with little bandwidth. I don't know how much bandwith a commercial FM radio station (88-108 mhz) uses, but it's probably more like 100 khz (after all, it's music.)
If you start reducing the bandwidth used, you lose data. If it's an AM signal, you'll start losing the higher frequencies. I'd have to think about what it would do to other modulation types ...
The real problem here is that the FCC has done some really wonky allocations of bandwidth. For example, the 72.450 mhz frequency I mentioned earlier -- the 72 mhz band is for R/C planes, but it's also shared with pagers. So 72.450 mhz is channel 33 for planes, but 72.460 mhz is probably used by a pager company. If they put their tower near our R/C field, and I fly my plane over near that end, and a page goes out ... their signal can overpower my wimpy little 1 watt transmitter, and guess what happens to the plane? (Actually, 1 watt isn't that wimpy -- R/C plane transmitters have a range of about 1.5 miles. But the pager tower may use something like 750 watts ...)
In any event, that exact same problem has happened in the 800 mhz band -- 801.4 mhz may be allocated to a police band, but 801.5 mhz may be used by a cell phone tower ...
Re:You'll need both (Score:2)
I have - I'm a chemist, so I do some spectroscopy. ;) I was more referring to the license situation the FCC has. It allots you, say, a 0.5 MHz bandwidth. Your transmitter is supposed to transmit in this band. However, say it sucks - the spectrum might not be as tight as it's supposed to be, and it might bleed over more.
For what
Re:You'll need both (Score:2)
Neat! My degrees are in physics and astrononmy, but alas I don't get to use them much `in real life' ... that would kick much ass if I make my living at it!
Right. But people were t
Re:You'll need both (Score:2)
Ah, I assumed by that he meant "800"+(lots of zeros to make the last digit nearly insignificant)+"1". But if you actually look at the number of zeros (which I'll admit I didn't do!), you are correct, sir.
And then there's harmonics -- 2.4 ghz should not affect 800 mh
Re:You'll need both (Score:2)
Impossible, or at least impractical. It would require losing the ability to use most of the spectrum -- because after all, whatever frequency you're talking about, there's a frequency that's 1/2, 1/3rd, 1/4th etc. of it, that could interfere with it.
Good transmitters have filters that almost completely kill the harm
Re:You'll need both (Score:2)
I wouldn't leave it unused, just try to shif things so that, say, two bands with extremely high power and use aren't directly "integered."
Also, I believe the relative power of the nth harmonic goes down directly with n, correct? As far as that goes, I suppos
Re:You'll need both (Score:2)
Easier (and cheaper) said than done. :)
It probably goes down exponentially -- 2nd harmonic is 1%, 3rd is 1% of 1%, etc. Not sure.
Absolutely. I don't
Re:You'll need both, and proximity matters (Score:1)
FM Radio transmitters that are close in frequency must have a certain physical distance between them.
Also consider off-carrier interference, particularly GSM mobile phones interfering down into the audible (kHz) range. It doesn't just affect hearing aids, but much in bet
Re:Exactly how crowded? (Score:1)
Each chunk (AKA band) of electromagnetic spectrum has a theoretical maximum throughput for information, which is related to the width of the chunk. Hence, we use the term "band-width" to describe the capacity of a link supported by electromagnetic phenomena.
Re:Exactly how crowded? (Score:2, Interesting)
Re:Exactly how crowded? (Score:5, Interesting)
There are two sets of frequencies for cell phones in the U.S. The orginial band at 800 Mhz(actually uses 825-895Mhz, IIRC) and the "PCS" frequencies at 1900MHz(1850-1990Mhz, once again, IIRC)
You'll find CDMA and TDMA networks in both bands. GSM uses mostly just the PCS bands, and Analog uses the 800Mhz exclusively.
Re:Exactly how crowded? (Score:5, Informative)
Then you get a combination of different technologies. Someone else mentioned TDMA, CDMA, GSM, and some others. Some of these operate in the same bandwidth without significant interference because the way they operate is so different. CDMA for example, doesn't suffer from the same kind of interference that TDMA, GSM and a few others do.
There's a technology called Ultra Wide Band that may take off over the next decade. While it covers a very large bandwidth (as the name would imply) that would normally interfere with other technologies, because of the way it operates, there's little, if any interference. The nice thing about it is, you can operate a number of different devices, each paid of sender and receivers has a "code" that allows them to communicate. Nothing else will interfere and many devices with different codes can operate in proximity.
Most technologies operate on the basic principal of sending a signal via the actual radio wave. They do this by modulating some part of the wave, usually frequency or amplitude (hence FM and AM radio).
UWB doesn't do that. Instead, it sends pulses very quickly (in picosecond lengths) and the pattern created by the pulses (think binary, on and off), are what are used to create teh signal.
Another advantage of UWB is that it works at a lower power (given the same range). Also, unlike the higher frequency applicatons (particularly when you get up to 5+ ghz), it doesn't have the same issues penetrating walls and such. Nice technology. Hope it makes headway.
Re:Exactly how crowded? (Score:2, Informative)
but, short answer, is no.
if you have a bandwidth of 1Hz, as you are suggesting, this is much too small to transmit any useful inf at any speed. for analogue voice, you need at least a bandwidth of ~30 Khz, and thats without the overheads of initiating communication, etc. now, GSM uses digital communication, which has a higher bandwidth, but means that you can multplex (which is essential, othewise you would just run out of spectrum).
add on top of that more BW
Re:Exactly how crowded? (Score:2)
(As an added bonus, they don't walk around going `Can you hear me now!')
Re:Exactly how crowded? (Score:1)
thats what i was basing it on.
Re:Exactly how crowded? (Score:2)
This allows it to reproduce frequencies up to 4 khz or so ... your ears can hear much higher than that, but it's not really needed for speech.
Shannons Law Re:Exactly how crowded? (Score:4, Informative)
The amount of bandwidth basically depends on you much noise there is around- you can pack much more data into a narrow channel if the channel has hardly any noise, whereas if the channel is very noise you'll need a wide channel to send the same data.
Also in practice you need a gap between neighbouring channels- the receivers need to filter out the other channels and they don't do this perfectly (although the better the receivers are, the closer you can pack them in.)
However Shannons law only deals with broadcast communications where everyone can 'hear' everyone else equally, if you use directional antennas then it doesn't necessarily apply- two communications could use the very same channels.
Depends how much bandwidth you want (Score:2)
IIRC cellphone networks are divided into 64kHz channels, each of which are shared by 8 phones. So each GSM phone has around 8kHz of bandwidth to play with.
FM Radio on the other hand i think
Re:Exactly how crowded? (Score:2)
Any time you modulate an RF carrier, you increase the total bandwidth or spectrum width required by said carrier. To use standard FM as an example, assume that Bw=bandwidth, Pd=Peak deviation (
Re:Exactly how crowded? (Score:2)
It depends how much noise is present in the communications channel and how much bandwidth (i.e., what data rate) your application requires. Look at Claude Shannon's classic paper A Mathematical Theory of Communication for a complete treatm
Short Range? (Score:5, Interesting)
Really... the main reason for the interference between cell and emergency is that they are all moving into the same spectrum space. 800mhz is a busy place these days.
True wireless (802.11a,b,g) are all in FAR different spectrums so other than cordless phones and some radar equipment interference is a moot point.
Open Spectrum (Score:3, Interesting)
NYC Wi-Fi (Score:5, Interesting)
The most interesting being the fact that I found 20 open and join-able networks on the corner of 20th and Broadway last week. I'd say some people need a lesson in security...
Also, I've seen people name their network things like "get the fuck off my shit" when neighbors try to join their network.
I'll also be interested to see if Wi-Fi networks effect piracy at all- what if the RIAA manages to crack down on piracy to a point that it cripples internet file trading (it wont happen, but come with me on this for a sec) and the only safe way to trade files is by sharing them on a local AirPort network. Then people can run around with their Wi-Fi PDAs with 1GB or greater flash cards, and download stuff from open networks they find on the street.
20th and Broad? (Score:3, Interesting)
It looks like companies don't use 802.11 hardly at all, rather, the more residential a neighborhood, the more prolific the access points become.
Unfortunately there's virtually nothing near the Staten Island Ferry (I live in SI) other than that damn Starbucks that closes too early and the V
Re:20th and Broad? (Score:1)
I don't think larger companies have a need for 802.11 yet. Not until Wi-Fi PDAs get popular. It's still a better technology for commercial/residential use.
Re:20th and Broad? (Score:2)
I like to be able to access the internet anywhere in the city with my PDA, and I am happy to allow others like myself free access in my local hood.
Re:NYC Wi-Fi (Score:1)
Apropos misuse of "effect"... Until recently I allowed all comers to use my Wifi connection (albeit at reduced bandwidth, about 128K shared between all strangers) for anything except connections to port 25. I'm adjacent to a nice outdoor public space with comfy seating so I figured it would be the neighborly thing to do.
I noticed that a few people were on there non-stop around the clock (including when said public area was observably
Re:NYC Wi-Fi (Score:2)
I've started taking my PowerBook+airport card and a WiFi scanner with me on business trips. It's rare that I can't find an open wireless network when I need one. On the same trip near Reagan
here's a thought ... (Score:5, Interesting)
so that being an option, why not have the cell companies take over administration of all the systems in these ranges, subcontracted thru local government offices? have the companies then manage (and be liable for) the need for non-overlapping frequencies separating critical traffic from the general public. especially the ones that shouldn't be driving and yapping on a cell phone as they hurtle through traffic (you know who you are!!!)
and yes, i know this puts a consumer-driven entity in charge of systems that are depended upon by lcoal/stage/regional entities, but hasn't private enterprise often proven its ability to manage complex systems a tad better than the government? could be a re-birth of telecom spending and contracts (which could mean jobs, more bottom-line investing, more attention on the nation's eroding infrastructure
Re:here's a thought ... (Score:5, Insightful)
Bureacracy will inevitably develop when such systems reach a certain size, and bureacracies will inevitably suffer inefficiencies. But I don't think adding profit motive to the equation necessarily makes the systems run any better -- it just shifts the mandate of the organization to revenue generation by system maintenance, rather than purely system maintenance -- and consequently opens the door to Worldcom/Enron-type problems.
I would rather not have market forces detemining whether I get 911 service on my cell, thanks
Re:here's a thought ... (Score:3, Funny)
Re:here's a thought ... (Score:2)
All three examples shouldn't be considered as problematic free market. California never really deregulate it's energy market (the blackout is a result of misalign of incentive when price of hydro is freely adjusted). Privatised public schools endure as much as the shortcoming of public schools, while it may save some taxpayer's money for other issue
Re:here's a thought ... (Score:2, Interesting)
Re:here's a thought ... (Score:1)
Cell phone networks are designed to work most of the time. Cell phones would be outrageously expensive if the network was designed to handle peak capacity during a crisis.
Public safety types need an effective communication system seperate from public systems. Duri
Is the FCC doing its job? (Score:3, Insightful)
Re:Is the FCC doing its job? (Score:4, Informative)
I think this is caused because the FCC specs say that a device X must use frequency y, and less than backgound noise on other frequencies.
Now, every RF transmitter is a analog device and as such it's impossible to transmit perfectly in the mandated frequency, so some leak to the neighbouring frequencies is inevitable. Still OK, a single device X will not produce noticable interference, as it produces less than background noise.
Now, instead of one device, you get thousands of RF transmitters, and the interference starts adding up, finally surpassing the background noise.
I believe this is also the reason why people are worried of UWB tech as well.
Instead of measuring interference produced by a single device, FCC will probably have to move measuring the interference created by an operational, full network.
Ofcourse this begs to ask why FCC allocated 800Mhz for mobile phones while knowing public safety departments use it AND the whole fucking entire other world uses 900Mhz. Thus making american phones incompatible with the entire other world for a long time...
WiFi Is Not Near Public Safety Bands (Score:5, Interesting)
Ummm, no. Here's a frequency chart of the radio spectrum [doc.gov]. People seem to think everyone uses all frequencies and it's one big radio spectrum blob. Radio spectrum resembles IP space, except in this case you can't create more of it. Print out the chart on a big plotter, hang it on the wall and impress your techie friends, and consult it when a wireless article is posted on Slashdot.
K3NG
Backup measures (Score:4, Insightful)
I would've thought emergency services always had some backup mechanisms in place to get back to the station in case of emergency.
Heck, I even thought the dash-cam that police cars are all supposed to have also relayed video back to a surveillance team back at HQ. Apparently it is not so. With risky, unpredictable work like emergency services at hand, I for one, am surprised they thought of fallback procedures only now.
I know transmitting live video from the surveillance cams is difficult, and multiple backup contact mechanisms would be expensive (cellphones, satellite phones et al), but then, I thought these guys would be the ones who deserve it most of all.
Re:Backup measures (Score:2, Insightful)
Think Mayberry. I can tell you from first hand experience that these guys are equipped to write speeding tickets and bust 14 year olds for posession of dope, and are some of the lowest paid in the nation. They start at like 25 grand a year.
If there was ever a major emergency around here (like 9/11
ip6 and TCP/IP for all wireless stuff? (Score:2, Interesting)
Would a medium / long term soultion of ip6 and TCP/IP all wireless stuff make sense?
Re:ip6 and TCP/IP for all wireless stuff? (Score:1)
Artificial scarcity? (Score:4, Insightful)
Re:Artificial scarcity? (Score:2)
Nah, this is a technology gap, I think. What's in R&D and what's in production differ. Further, it's encumbered by backwards compatibility. If you go to the new technology, all of your old radios become basically paperweights.
There are technologies for making a smaller footprint. Comparing different signal formats for two-way, you have FM, which, when formatted for 2-way, uses 10-20kHz of bandwidth. Compare that to AM, which uses 6-10kHz, compared to single sideband (SSB), which uses 3-5kHz (usua
Range (Score:1, Insightful)
The reason it's not a problem has nothing to do with range at all. It's more because of the low usage when compared to other RF. If there were as many wifi users as mobile phone users, it would be just as big of a problem.
I don't recall this being a problem in the UK (Score:3, Interesting)
Problem is..... (Score:2, Interesting)
Do you really think that amateur radio operators will come forward and say "Hey, we've got bandspace to spare, take some of ours!"?
Maybe there should be more stringent standards on how much interference an appliance creates?
But personally I say we just eliminate the CB frequencies. Only those with too much spare time and no mobile phone use it anyways. Let it go and get FRS or GMRS for pete's sake!
Re:Problem is..... (Score:2, Insightful)
Re:Problem is..... (Score:1)
Do you really think that broadcast TV companies will come forward and say "Hey, we've got bandspace to spare, take some of ours!"?
Maybe there should be more stringent standards on how much interference an appliance creates?
But personally I say we just eliminate the broadcast TV frequencies. Only those with too much spare time and no cable service use it anyways. Let it go and get cable or satellite for pete's
Re:Problem is..... (Score:1)
No one wants to give in.
KE4WLE
Darned Towers (Score:1)
The tower was set to be built just down the street from my house in the neighborhood park, which is un-fun, to say the least. Fortunately, starting a silly grassroots community NIMBY campaign proved unnecessar
Airport zoning (Score:1)
In Texas, even the state cannot do it - our community (pop. 7700 and shrinking, about 100 miles to any other population center) - had to create an airport zoning board, adopt a state-recommended rule restricting construction in the airspace for the airport, meet three times, etc. before we could prevent such things.
While the FCC
Monitoring dead spots (Score:3, Insightful)
Cell providers (and most commercial radio operators) know that the precise interrelationships are always changing. New buildings, new transmitters, malicious/accidental interference. Most wireless carriers send drivers with GPS/inertial locators and signal strength meters wandering about their coverage areas to locate areas of poor coverage. "..hear me now, Good!"
A friend once showed a map drawn by a wireless system installer showing that with X number of towers the entire coverage area would have maximum signal strength. Most government entities would stop here, believing the installer. But this wireless company did a standard mapping of signal strengths and found inadequate coverage all over, the number of towers had to be almost doubled from the original estimate and dead spots still exist.
Good radio operation is more than just getting a license and standing up a tower. Whining that the FCC should step in just becuase you're too lazy to fix you own stuff is irresponsible.
Wireless Interference (Score:5, Insightful)
What a load of crap! It's not the problem of the wireless providers, it's a problem of coverage due to poor system engineering.
Most, if not all, 800 mhz emergency service systems operate on what is call a "Trunking System". What this is, essentially, a system of linked towers that communicate with the vehicle or officer on the street, then relay from tower to tower ultimately connecting to either the dispatcher or another officer. These systems are designed to be interoperable with each service, such as police, fire, ambulance, etc, so a single dispatch facility can communicate with everyone, and all services can communicate with each other.
To work effectively, you must have sufficient towers properly placed to assure that there is no dead zones. Given the expense involved in site purchase, permits, tower erection, equipment installation, and backup generators, the bare minimum is pretty much the rule. Plus, you cannot physically survey the entire area of coverage, you use topo charts to try to make sure your engineering is sound.
To blame the wireless providers is silly and stupid. Modern 800 mhz equipment is very selective, most newer systems operate via spread spectrum digital, and the chances of interference are minimum.
Additionally, emergency services have priority so if there is a provable case of direct intererence, the wireless provider must take steps to either stop the interfering signal, or cease operations entirely.
Good timing! (Score:4, Interesting)
I am the Assistant Chief of a volunteer department [lutzvfd.com] north of Tampa, Florida. We operate off of the 800mhz radio system, and for all of the money we spent on it, you would think it would work better. Instead, we have spots where we can hear but not transmit, or just plain not get reception at all.
While we were talking about this one of the Hillsborough County chiefs brought up the fact that when he is at headquarters (where our central towers and dispatch are) he can't use his little car-alarm-door-unlock-gadget-thingy unless he is almost touching his vehicle. When he is at home, he can activate it from 200-300 yards away.
We have always blamed it on the hardware and crappy company, but now I think I might have to look a little more into what other kinds of interference would cause transmission and reception problems in the areas where we are having difficuly.
Re:Good timing! (Score:3, Informative)
I'm going to ask a question that may sound snide, but is actually very serious: Why did you go to 800MHz? Were you using VHF-Lo, VHF-Hi or UHF before? What was the coverage like?
I ask this because in my hometown of Selkirk, NY, they use a system that is a hybrid VHF-Lo and UHF system. VHF-Lo (46.06MHz) covers the town, and the UHF is only used as a remote base, with the base radios at the three fire companies talking on 455.6375 and listening on 460.6375. It works very well. My father, who is a memb
Intermodulation (Score:2, Interesting)
Re:Intermodulation (Score:1)
800 MHz band. In this case, additional filtering won't help as the receiver needs to hear signals in the band of interest.
I am guessing that when a public safety radio is near a cell tower, the radio does not have enough dynamic
range to hear the desired weak signal when there is a strong interferer nearby. The AGC limits the gain of the public safety radio based on the undesired cell signal. This would cre
Re:Intermodulation (Score:1)
Re:Intermodulation (Score:1)
Provided the transmitters, especially the amplification stages, are properly sheilded from the outside world. The frequencies aren't generated at 1900MHz, they start at lower frequencies and mix their products to acheive the final result. Given that a perfect Faraday Cage [wikipedia.org] is difficult to acheive when you need to poke holes in it in order to get things such as power and data in, as well as final signal out, you get weird leaks, causing interference to other
Re:Intermodulation (Score:1)
Nextel is to blame (Score:1, Insightful)
What they are proposing is moving public safety to different bands, and giving themselves some more prime spectrum for free. They offered $850 million to move public safety into different bands, which is of course, not anywhere near what the spectrum that Nexte
Contemporarizing spectrum regulations (Score:2, Insightful)
This brings out the need for changing spectrum regulations from auctions to open spectrum access for three specific reasons:
Technical: The system of allocating a particular frequency band to a single user is based on outdated technology. Early receivers and transmission schemes were such that we needed to be concerned about the possibility of interference. The development and imple
Shut down the "Emergency" networks (Score:2)
Give ever cop and fireman a cellphone,
and the problem is solved, public funds
are conserved, and the traffic becomes
protected and routable with QoS guarantees.
Re:Shut down the "Emergency" networks (Score:2)
Ah yes, let's throw more technology, ergo more complexity and the accompanying greater chance of a breakdown into the picture.
I have a better idea. Let's abolish networks altogether for emergency, and go back to simplex on the VHF band. It works really, really well.
The FCC can't move mountains (or hills) (Score:2, Informative)
Technical Standards (Score:2)
Re:Technical Standards (Score:1)
Fear BPL! (Score:1)
Their thinking is limited and short term. (Score:1)
Reorganization would be rife with all manner of contention and expensive reconfiguration. But as painful as it may sound, this i