Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!

 



Forgot your password?
typodupeerror
Check out the new SourceForge HTML5 internet speed test! No Flash necessary and runs on all devices. ×
The Internet

AM Frequency Hinders ADSL Capacity 124

hajmola writes "a recent study has shown that AM radio may be causing problems for ADSL. According to this story at Network World, interference from AM stations can slash high-speed bandwidth by 40% on approximately 15% of ADSL connections. While AM interferes with download speeds, it does not affect upload speeds. AM frequency only affects ADSL and its subsets (not SDSL), including rate adaptive DSL and G.lite. "
This discussion has been archived. No new comments can be posted.

AM Frequency Hinders ADSL Capacity

Comments Filter:
  • When you start with something like 1.5 Mbit/s download, a 40% drop in speed should not make service infeasible. It is a good thing that the upload speed is not affect as it begins lower(?)

    I wonder how this will affect AOL's strategy to push the ADSL technology as opposed to bust into the closed cable rings.

    Please visit FreeDonation.com [freedonation.com] - You can donate Food and Medicine for FREE to Save Children (You can donate once EVERY DAY). The donation is fully paid by corporate sponsors with the money they would have spent anyway on advertising. There is no charge to you.
  • How can we possible "ditch the am"?
    if you'd noticed, AM radio interference comes from anything... your monitor, computer... even your mouse! But these stations are broadcasting at a much higher amplitude... and AM radio covers everything from Medium Wave (AM) and Shortwave and many other bands. We need to find some way to protect our DSL lines from outside interference. You can't eliminate the interference because of inferior technology.
  • So how do we know ADSL doesn't interfere with AM radio? For the love of god, this damned technology could be what's keeping me from my broadcasts of "the joy of cooking" on NPR!. Oh the humanity!
  • People are finally figuring out they should have their phonelines SHIELDED! what a concept! :-)
    (I've got my phones running through CAT5 now and have never had better connect speeds)

    I guess the problem now is what to get rid of - AM radio or ADSL? let's see - AM Radio... gives us - talk radio and spanish stations over really bad mono audio. ADSL gives us nice bandwidth, neat lookin router thingies (I like the little cisco/netspeed router thingy), and more bandwidth. :-)

  • I think your ADSL is interferring with your brain waves.

    And, lest there be any confustion, NPR kicks ass. It's the least biased of any broadcast media news source. Plus I like Chinwag Theater on Sundays at 6pm :)
  • Wouldn't this mean that both phone lines and AM radio stations are in violation of part 15 of the FCC rules? The AM radio stations are guilty of causing harmful interference, and the phone companies are guilty of not accepting interference gracefully.

    -Rigel
  • I have ADSL and a radio..The radio is near the ADSL modem thing. I turned on the radio and it didn't work... till I hooked up an AM antena.. Then it seemed to work fine.

    My DSL seems to work great (as advertised) except when Bell-Atl removes my dial tone for no apparent reason as they've done from time time (Just to keep me on my toes?) .
    The fact that I'm really close to the CO might have something to do with it.
  • CAT5 is UTP, unshielded twisted pair.
    See, unshielded, as in, no shielding
  • Part 15 applies to consumer electronics (cordless phone, computer, etc). I doubt part 15 applies to broadcast stations :)

    Ryan
  • I don't know about other people, but I live right next to the telco switch basically, and I get the speed as advertised ( 1.5mbit/128K ). Can't wait untill 5 years time when we'll be able to put to use all that fiber pacbell is laying around here. Ofcourse I probably won't live here then... and I might have to deal with bellsouth which I would not look forward to at all.

  • So thanks to the guy giving play-by-play of the local junior high football game in panish on AM560, I lose somewhere near 2MBps? I'd sacrifice the bandwidth only if people would play decent crap on the radio...
  • So if AM interferes with ADSL, and high voltage power lines interfere with AM, does that mean Slashdot will load faster if I live under high voltage power lines? Or does that just mean I'd get brain damage while reading Slashdot?

    Damn, sometimes it's hard to pick the lesser of two evils...

  • by turg ( 19864 ) <turg@winston . o rg> on Tuesday November 23, 1999 @07:08PM (#1509026) Journal
    The rule forbid "causing harmful interference" to radio stations, by appliances, not vice versa. The ADSL line is "accepting interference gracefully" -- by allowing its own performance to degrade rather than fight back against the interference (which would involve causing harmful interference to the radio signal). This is precisely what is required by the regulations to which you refer.

    Hope this helps


    -
    <SIG>
    "I am not trying to prove that I am right... I am only trying to find out whether." -Bertolt Brecht

  • many light dimmers will hash out your am radio when you turn them on, plus they can go all the way up to 3 MHz. This really should not be a suprise, as telephone wires are essentially longwire antennas.
  • ASDL. Sounds nice. Heard a lot about it. But there's one little problem: I live in the netherlands. Ofcourse, our government claims that we are one of the leading countries on the digital highway (NOT!), but new technologies like ASDL are outdated before they are implemented here. I know of one company that's currently providing ASDL-internet-access, but it's only a pilot program, for 300 lucky inhabitants of Rotterdam. I (i live near Utrecht) have to wait a couple of years, I think.....

  • I bet adsl would really suck in venezuela w/ over 180 AM radio stations. Oh wait, what wouldnt suck w/ that many AM stations and little/no fm.
  • by gargle ( 97883 ) on Tuesday November 23, 1999 @07:28PM (#1509032) Homepage
    I happened to attend a talk last week by Professor Cioffi of Stanford University, the inventor of the DMT technique widely used in ADSL. The issue of AM interference with ADSL transmission came up during his presentation. However, what DMT does is to optimize the transmission by reducing the strength of the signal sent on frequency bands where the noise is high (or where FCC regulations do not permit transmission due to emissions produced by the DSL line), and increase the signal strength on bands where the noise is low. If I recall correctly, AM interference is accounted for and the actual ADSL specs do not transmit a significant amount of energy in the AM frequency bands, so it's strange that this article identifies AM interference as a problem.
  • It's about time AM left the air. Besides perhaps a little bit of nostaglia and an unexpired radio band license, I don't think there is a single technical advantage. I think the list of disadvantages go on and on .. poor spectral efficiency, wasted carrier energy, high sensitivity to noise, poor sound quality ...
  • Wait a minute, I thought certain frequencies were reserved, and AM radio happened to be one of them. So why now is this being noted? You would imagine that, sitting in a lab Engineer Bob would think, "Hey, this frequency is between 400-1400KHz, I wonder what else is in that frequecy range".

    Actually, wait another minute. How can you pipe 1.5Mb/s over AM frequencies, anyways? Don't you need 2x frequecy to send x b/s? Doesn't Nyquist theorem state this?

    Ah, here it is:
    "The Nyquist-Shannon Theorem states that an analogue signal of bandwidth B can be completely recreated from its sampled form provided it is sampled at a rate s equal to at least twice its bandwidth."

    Found at: (no, I am not going to piss around with HTML tags)
    http://www-dept.cs.ucl.ac.uk/staff/S.Bhatti/D51- notes/node4.html#equNyquistShannon

    Sorry, just a bit of communication theory from a sleep derprived engineer-in-training.
  • by layne ( 15501 ) on Tuesday November 23, 1999 @07:31PM (#1509035)
    I remember this mention [nwfusion.com] in a study done by avalon.net two years ago. This piece [nwfusion.com] gives some more detail regarding frequencies at cross purposes.

    As it mentions, a T-1 loop running in parallel to your POTS pair can also cause drop-out in your DSL frequency spectrum.
  • I can't wait till I hear someone tell a customer their ADSL service is screwed because they're picking up interferece from the Art Bell show on the AM band. *g*

  • Actually, wait another minute. How can you pipe 1.5Mb/s over AM frequencies, anyways? Don't you need 2x frequecy to send x b/s? Doesn't Nyquist theorem state this?

    No, because in general bits/s != samples/s. Bits per second equals cycles per second TIMES BITS PER SAMPLE. You can typically get a lot more than one bit per sample, depending on the resolution of your A/D converter and the effective signal to noise ratio.

    Put it another way: The Nyquist theorem is about discrete sampling of an analog waveform: the samples themselves are analog values. When you go further and digitize the samples, now you can start talking about bits per second.

    --Seen

  • by mgrant ( 96571 )
    You mean those big numbers underneath the real station numbers on my clock radio actually do something?
  • AM Radio is great! Its signals bounce off the atmosphere allowing stations to broadcast incredible distances. At night, AM stations on the west coast of the US can be heard up and down the coast, east to the Rockies and by all the ships in the Pacific. That compares to the paultry few miles DSL works before slowing down.
  • You're not kidding.

    I live in San Jose, within about a half mile of a telco CO, and get the full 1.5M/128K speed. But, when a housemate turns on a dimmer light, it goes completely down the toilet! The ADSL box craps out completely, losing sync and dropping TCP connections.

    If you get DSL, don't throw out your modem...

  • Errr... I don't think the sampling theorem applies in this case. The sampling theorem applies to sampling an analogue signal at discrete times. You have to sample at twice the highest component frequency to avoid aliasing (high freqs looking like low freqs).

    I think what would apply is Shannon's theorem, which relates the information carrying capacity of a channel to its bandwidth and the amount of noise.
  • This could be an interesting opportunity for some daring developer. How about this for an idea: The ADSL modems characterize the link and determine what frequencies they're receiving interference on. They use this information to control a separate AM tuner to discover if the interference is due to an AM station. If it is, they use the demodulated AM signal as an input to a noise filter to reduce the AM signal's power in the data transmission, and voila! You've nearly perfectly cancelled out at least one source of heartache.

    Thoughts from the peanut gallery?

    --Joe
    --
  • CAT5 cable can be either unshielded or shielded. Most installs I've seen use cheap UTP cable.

    -A.P.
    --


    "One World, one Web, one Program" - Microsoft promotional ad

  • let's see - AM Radio... gives us - talk radio and spanish stations over really bad mono audio.

    AM Radio also allows people who are not in line of sight of an FM transmitter to receive radio. Think of the worker who put the lettuce in your salad tonite; it may be his only contact with the world outside of the salinas valley. (think NPR--only in Spanish)

    Be careful what you choose to trivialize.

    PS yes, I know the issue is carrier frequency, not modulation scheme.

  • by Rick Evans ( 48110 ) on Tuesday November 23, 1999 @08:56PM (#1509050)
    One thing that often gets missed in this discussion is that amateur (ham) radio is also degraded by ADSL.

    Two prime frequency bands: 75/80 meters in the 1.8-2.0 Mhz range, and 40 meters in the 3.5-4.0 Mhz range. In both cases, the amateur radio operator is often trying to receive a signal from a 100 watt (typical) transmitter in a foreign country. The ADSL 'white noise' overpowers the signal.

    Amateur radio shares many traits with open source software. Cooperation and sharing of information are respected qualities in an operator. A non-trivial number of hams still build their own equipment or modify the design to improve performance.

    I think ADSL is pretty cool, and wish both of my hobbies could co-exist.

    Rick Evans, KG4FER
    Orlando, FL
  • by Wakko Warner ( 324 ) on Tuesday November 23, 1999 @09:02PM (#1509051) Homepage Journal
    "I can't download pr0n as fast as I should be able to, so let's ditch AM radio!" Now, let's see which came first, has more users (listeners), and is generally more useful to a greater amount of people. That would be AM radio. Maybe ADSL should be the one to have to change, wouldn't you say? Or, should I and millions of other people give up our baseball games, news reports, and weather so you can play Quake a little faster? It seems awfully ignorant to want to get rid of an entire medium just because another, poorly-designed, newer medium chokes because of it.

    - A.P.
    --


    "One World, one Web, one Program" - Microsoft promotional ad

  • So does this cause packets to be dropped/corrupted, or does it interfere in some other way?
  • I've read reports in the German mag c't about hobby radio people who complained that ADSL lines were interfering with their communications.

    AFAIK the german T-DSL uses a slightly different standard than G.Lite to allow both ISDN and DSL on one line.

    The main problem is that the user end of the line is not shielded and thereore both AM radio and the ADSL lines interfer.
  • by Anonymous Coward
    Like... setting the phone line on fire? I mean, if the packets are getting through intact, there is no problem. In any case, what is almost certainly happening is that the unshielded, poorly wired, losely twisted (if at all) phone wiring in homes is picking up AM transmissions at low power, which disrupts the ADSL signal. Much less likely is that it interferes with the router itself or the phone lines between your house and the phone station (which are usually much better wiring that in homes). For optimum quality, plug the DSL router into the phone line right where it enters your house, then run all extensions in your house off of the filtered phone line on the DSL router. Then run cat-5 wiring to whatever computer you want to hook it up to.
  • Well in my area the cable line provider is also the only isp - no competition. There's one adsl line provider but lots of isps. My adsl line is reliable, and faster than cable in the area. My friends cable is always going down, and he averages half my speed. Cable users can't even saturate my *upstream* bandwidth (384 kbits/s). I wouldn't even notice when one is on my ftp if my router lights didn't flash.

    I wouldn't get interferance from AM radio transmitters anyway, they're all on top of the mountians.

    (adsl user, Vancouver, BC)
    Cheers,

    Rick Kirkland
  • When you start with something like 1.5 Mbit/s download, a 40% drop in speed should not make service infeasible. It is a good thing that the upload speed is not affect as it begins lower(?)
    Yes, but 40% is still 40%, regardless of the speed. You're paying for 100% speed, and get only 60%. That's not good. When somebody uses his/her ADSL mostly for downstream traffic (as you would if you're not running a server), the 40% really matters.

    The real problem lies in the poor cabling: it's designed for low quality analog voice connections, not for (relatively) high speed digital connections.
  • It's about time AM left the air.
    This problem is with ADSL, not with AM. If the article stated: "most drunk drivers get killed when hitting a tree", you'd say "okay, let's axe down all trees".
  • How about Anti-Interference. If you get an antanne and broadcast noise, it may clear up the problem because all the intereference might collide with the anti-intereference and go away. That way there would be no more intereference near the cables.
  • AM has always been a geek toy
    From talk radio to shortwave boys
    Too late to ditch
    Anyways, isnt it
    Part of universal background noise?

  • by Wakko Warner ( 324 ) on Tuesday November 23, 1999 @11:06PM (#1509064) Homepage Journal
    In 10 years, people will laugh at what we consider "fast". Do you honestly think people will only be able to get by with a mere megabit per second of bandwidth? On the other hand, I anticipate I'll still be able to listen to a baseball game by the pool or at the beach on my little cheap AM radio.

    Oh, and until FM radio can be broadcast over hundreds of miles, which AM can do easily, there will still be a need for AM radio. There's a *reason* AM is still around, and it's not simply because stations own the bandwidth still.

    Wake up, indeed.

    - A.P.
    --


    "One World, one Web, one Program" - Microsoft promotional ad

  • I want DVD-quality MPEG2 over IP, damnit! (Yes, I know the occasional lucky bastard should be able to get 8 Meg downloads over ADSL but generally, 1.5 is all you get)

    Will MPEG4 come to the rescue or will another line type?
    --

  • What about cable modems - the're available around most parts of Amsterdam now, and there is a special of NLG69 per month with free installation (and no telephone per minute charges !!!!!!).
  • Just dumped my cable modem because of massive bandwidth loss due to too many people on my
    segment. Scheduled to get adsl shortly as a replacement. The good news is at least i got
    free installation and the dsl company also offers SDSL(for 3 times as much of course).
    I think i shall not get rid of my dialup isp just yet. Kept it even after i got my cable modem just in case.
    I think ill start sending e-mails now in anticipation, to all the AM stations in the area.
    That should be about 40 e-mails if i remember correctly.

    Actually what do people use there AM radio for? Probibly most listen to games
    and Art Bell anyhow. If thats the case you can get online broadcast's of it all anyways.

  • by revnight ( 8980 ) on Wednesday November 24, 1999 @12:22AM (#1509071)
    adsl isn't even going to be the largest factor affecting hf. as i recall, idsl broadcasts across the entire u.s. hf amatuer spectrum...

    more details at http://www.hamradio-online.com
  • by revnight ( 8980 ) on Wednesday November 24, 1999 @12:32AM (#1509072)
    my apologies...vdsl is the *dsl technology i was referring to.

    if you want to read a bit more about this, check out this link:
    http://www.hamradio-online.com/library99.html#ju l1999
  • by RISCy Business ( 27981 ) on Wednesday November 24, 1999 @12:37AM (#1509073) Homepage
    Not necessarily.

    Bear in mind, AM signal strength is directly relative to several key things; distance from transmitter, power of transmitter, and frequency.

    I'm guessing (I am TOO tired to read the article and make total sense of it right now) that they have already isolated which frequencies effect ADSL. That leaves it to a simple matter of determining a way to filter out the noise from those frequencies at each end. That, unfortunately, is not easy.

    However, this surprises me not at all. Cable modems have similar problems. Like Digital Cable. I'm sorry, but two *VERY* busy digital signals over a single coaxial line just will NOT work. Granted, the cablemodem should be operating around 6MHz and your audio/video signals are around 40MHz IIRC, you still run into the problem that those are *baselines*. They go a certain amount either way, with another bit thrown in for tolerance. And end up crowding eachother out. Then at the cable plant, you have things like RF interference from your wireless reception/transmission equipment, and such crap. Things like ingress and dB loss. That's why there's the Cisco uBR7246 (Universal Broadband Router). It's designed with all that stuff in mind, at the cable plant. Once you leave there, you're on your own.

    There's really not much that can be done but to compensate. The chances of the FCC ruling ADSL more important than AM radio, which is older than ENIAC by probably a quarter century or more, are very slim. So it's going to be up to the designers and implementers to compensate.
  • by Hyper ( 5220 )
    The upload speed may not be affected, however it does give the ISP an excuse to option the upstream speed down and blame it on poor line quality. I have first hand experience and as a result I am now a cable ISP subscriber. :( hypedawg
  • Well, since my am cb causes noticable interferance to the phone line (not enougth to upset my modem), looks like i'll have to give it up before i get asdl.
  • Get your wavelengths right. 1.8-2.0 MHz is 160m and 3.5 to 4.0 MHz is 80m/75m (40m is 7.0-7.3 MHz). A good write up on removing harmful interference can be found here [contesting.com] on the 160m mailing list (watch out if you join, the list admin is a real asshole). There is also a email list on this sight specifically for RFI. I also think ADSL is cool. The cable companies are screwed (especially for business) because they can't gurantee uptime or bandwidth.
  • Broadcasting noise will just add more noise. The "may" in your statement is simply false.

    The "collision" which you are hoping for can only happen if you transmit exactly the opposite of the signal which an antenna will receive, such that the original signal and your opposite signal arrive at that antenna at exactly the same time. However, you have to send your opposite signal before the target antenna receives it, you have to send your opposite signal from the proper distance and time for it to reach the target antenna at the proper time, you have to send exactly the opposite signal so you have to listen to the original signal before the target antenna listens to it, and your cancellation signal only works at that single target antenna -- every other location just hears more noise. That's why when some government jam shortwave signals what the radios hear are various mixtures of noise. You can hear the same thing on a crowded AM/Shortwave frequency.

  • Bah....

    Even though you don't want to, you should remember that not everyone is a high-speed computer geek. If people still didn't listen to AM every hour of every day they would not be broadcasting. Go out hunting sometime, and while you are taking the 8 hour drive to Detour in the UP try to get some FM radio stations.
  • I don't think there is a single technical advantage

    The advantage is range. On a good night back home in NC, I could listen to Mets radio broadcasts on AM from New York. No way does any FM station have that kind of range...

    and yes, i listened to the broadcast from NY b/c there was no local broadcast.

  • Why would we ditch AM radio, when ADSL will probably only be available to maybe 20% of the entire US population, whilst AM radio is available to damn near every person in the country, regardless if they live in a really big ditch or not.

    Of course if the FCC did decide that they wanted to junk the AM band, you'd then need for the whole International Telecommunications Union to agree to ditch it too. Fat chance in hell if you ask me. There is lots of money that the AM broadcasting industry has to toss about to get there way.

    Perhaps a better idea would have been to implement ADSL using spread-spectrum technology.

    But in the mean time, ADSL users don't have much of a choice but to accept the interference that drops there packets.

    Amateur radio operators have been dealing with cable companies on similiar issues for quite a few years now. It just so happens that cable channel 19(I think its 19) video signal falls on 145.25MHz. Right towards the low-end of the 2 meter band. This of course causes all sorts of problems with amateur radio communications on this frequency because of shotty coaxial cable. But the neighbors of course, bitch a storm when channel 19 gets washed out by the interference from the crazy guy with all of the antennas on his roof down the street. Well guess what if you don't like it bitch at the cable company. I have the right to be there in the ether, they don't.

  • That's why we have FM now !! wake up !
    What do you think will be more important 10 years from now ? The old low-quality mono AM radio or high speed net access ??


    AM will be around for a very long time to come. AM transmitters and receivers are far simpler to design and use far less components than FM.

    Yes FM is higher fidelity but AM wins hands-down in the "simple to set up" category, which is important in any kind of emergency (I'm thinking TEOTWAWKI) situation.

  • I live in San Jose, within about a half mile of a telco CO, and get the full 1.5M/128K speed. But, when a housemate turns on a dimmer light, it goes completely down the toilet! The ADSL box craps out completely, losing sync and dropping TCP connections.

    Sounds like you need a crash course in EMI/RFI elimination.

    Try using shielded cable for your ADSL modem (as in install a shielded cable, shield grounded at one end only) from the demarcation point to your modem. Make sure the modem's grounded. If you wanna take it to the n'th degree, make sure your computer and the network cable between the computer and the modem are grounded. Ideally you want a single-point (star) ground. Make sure the dimmer's grounded.

    Use good RF grounds. (copper braid either to your copper cold-water pipe coming in from outside or to a network of 8' to 12' copper rods which you drove into your backyard)

    Get a dimmer that dims on whole-cycle periods instead of chopping up each cycle. That in itself will eliminate a LOT of interferance. Take a ferrie rod and wrap the power lines from the dimmer to the panel around it a few times, like this (may need to view in a monospace font):


    \\ ^^ ^^ ^^ ^^ // --- line and neutral
    @@@//@@@//@@@//@@@//@@@//@@ --- ferrite rod
    VV VV VV VV VV


    Do the same for the power cord for the modem.

    As I stated, it shoudl go between the panel and the dimmer, like this:

    panel --- ferrite rod --- dimmer --- lamp

    These tips should help quite a bit...
  • They really need to turn over the radio spectrum to the public for short-range Internet wireless systems. On the other hand they should sheild those lines too. No reason to be stupid about it. :)
  • Frequency bands are reserved for transmission through the air. That doesn't mean that you can't use them in wire based transmission. Further, the FCC emissions regulations require that wire based transmission not interfere with air based transmission. It is entirely up to the wire based system to protect itself from interference caused by air based transmission. This is why you can't use a cell phone in a plane. The plane is protecting itself from interference from air based transmissions.
  • As I was falling asleep, I realized my mistake on the wavelength --> frequency mapping. I was going to post a correction, but realized that you (or someone else) would do it for me before I could log back on.

    You're right.

    Rick 'doh' Evans
  • Maybe this might convince you slow coach Americans that adopting DAB is a Good Thing(tm)....

    DAB uses MP3 .'. DAB much be good right?
  • Amateur Radio is authorized to radiate in the bands assigned to it.

    ADSL, cable, et cetra are not authorized to radiate at all in those bands, the AM ones, or any other frequency; if it does, it is violating FCC regs. Simple as that.
  • C'mon now - you're experiencing the benefits of higher grade copper and tighter twist, not shielding. STP cabling has different signaling characteristics, for one. For the other, unless the link is shielded end-to-end, it isn't truly shielded. For a third, if you don't have a shielded jack to plug the shielded connector for your shielded CAT 5 into, you are going to run into problems with grounding loops, at which point you would be much better off with UTP.

    In the end, CAT 5 UTP has more than enough twist in it to compensate for all but the most noisy environments. After that, you're running STP cabling, which more than likely means you are running your network over Token Ring (see 'signaling characteristics' above). Even nasty cheap-ass CAT 5 is going to be much better than phone cabling, hence your observations. The 'shielding' you think you are seeing is just a protective wrap for the wires, that way when people walk on them and what not the copper doesn't break between the jacks. This is also why you see stranded core used for hooking up desktops to the wall and what not, and solid core run through the walls (stranded core is less prone to breakage than solid when it comes to tight turns, people stepping on it constantly, etc. but it is more expensive - you can save money on your total plant cost by taking advantage of the fact that nobody is going to be stepping on and monkeying around with the cables in the walls that much).

    Anyway, I agree, if you are having a house built or rewired, run CAT 5 UTP for both data and phone, or at least CAT 3 for phone. It does make a difference.

  • The article didn't mention any frequencies on which the interference might occur.

    My multisync monitor causes AM interference in my house, but my guess would be that the incoming ADSL signal would be much stronger in comparison.
  • I have ADSL, but have never noticed any degredation. However, there are several AM towers in the area, and I can get AM radio stations to play over just about any electrical device with a speaker. My old answering machine plays oldies, my old phone picks up interference, etc.

    Is this because of the wiring in the house or the wiring going to my house? I would think it's the in-house wiring or the devices themselves because the phone lines are underground around here.

    My ADSL wire runs only 15 feet or so to the splitter in my basement. Maybe I should really test my bandwith - very few things on the web give you an accurate idea of the speed. I'm supposed to get 2.2 Mb/s...


    Dozer

    "The dumber people think you are, the more surprised they're going to be when you kill them."
  • I live about a mile from KDKA 1020 in Pittsburgh PA, It's the oldest and strongest public radio boradcast in the world (some people can pick it uip in their dental fillings).

    I have CAT 5 run from my Network Interface Device to my DSL adapter, not including the 4ft phone cable from the cat 5 to the dsl adapter. and I get most of my full bandwidth at 640K.

    I guess I'm really lucky because I would assume that a lot of the 15% affected are near KDKA. (Or would be if Bell Atlantic would get more neighborhoods rolled out.)
  • Actually, the capacity of a channel is proportional only to the signal to noise ratio of the channel. Were your application of Nyquist's theory valid, you could go no higher than 7200 bps over POTS (plain old telephone service). Now, look real close at your modem. I'll bet it's going higher than 7200bps.


    The trick is that a phone line has a very high signal to noise ratio, and you can make use of this to move more bits than the line has hertz of bandwidth.


    Now, over a radio link, your signal to noise ratio drops, and you have to use more bandwidth to raise the S/N up. Over wires (like DSL) you are able to maintain a better S/N ratio. However, when your local AM station bleeds in, you lower the S/N ratio and thus reduce the bearing capacity of the channel.


    However, part of DSL is avoiding the frequencies that have interference, and using the ones that are clear. Yes, if the line were completely clean you could get more throughput, but crosstalk from the other lines in the bundle, noise from AM and CB radio, and attenuation from the fact the wires were not designed for RF frequencies all reduce throughput and were allowed for in the spec.

  • Your ham radio experience was completely atypical. And TCP/IP and Linux are used widely by hams. Try again, perhaps you were being wound up (hams do that too). --
  • I can't remember the URL, but recenty I read on some HAM site about how ADSL really messes up shortwave radio. It looks to me like those who made up the ADSL standard should have specified shielded cables.
  • Sure, higher fidelity, but the signal degrades more easily. Does anyone use AM Stereo btw?

    And, if we designed them today, we'd use compression and massive error correction, probably reducing the bandwidth both need as well as boosting the fidelity.
  • Actually, that wouldn't be a bad idea. AM radio, as many have said, transmits very well, and is easy. So we should keep it, but do we need as wide a space for it (not that AM radio is too wide, but...). Ditto with FM and TV...

    Maybe space for some of AM, and a TV channel or two. Everything else would be better served, in metropolitan areas, by using copper or fiber to transmit that and freeing the airwaves for things that have to be wireless.

    And with enough airspace, you could simply listen to streaming news reports via a cell-phone -> car stereo link, if you needed that. I don't think music stations, as the sole players of new music, will be around much longer with the ability to stream a custom choice of music, etc.

    I see some great uses for widecasts, namely in the interior of British Columbia where I grew up, or the even less populated northern edge of the prarie provinces. But, in cities where cell phones do more good, I think we should be trying to reallocate space, move things aroung, and make more room for digital cells.
  • CAT5 is UTP, unshielded twisted pair. See, unshielded, as in, no shielding

    The twisting of the cables has a shielding effect (two wires in parallel make a good antenna; but twisted, they do not). So they are effectively shielded, against frequencies whose wavelength is of the order of the length of a single twist.

    The problem is that most phone cabling isn't twisted with any consistancy. So that means there are lots of mini-antennae with slightly different resonant frequencies all picking up interference.

  • Actually they make light dimmers which don't interfear with any other devices. We picked those up for our old light dimmers and they actually worked.
  • yes, I know the issue is carrier frequency, not modulation scheme.

    But that is the issue; at lower frequencies, you don't have the bandwidth to do frequency modulation, so amplitude modulation is the only way to go. Or have only 10 possible radio stations :).

  • As the AC posted, radio stations have an FCC license for broadcasting in a specific frequency range. ADSL is not a broadcast signal. It's a captive signal designed to flow down a copper wire. As such, ADSL doesn't have the signal immunity that all other (high frequency) broadcast technologies have. The radio (read: broadcast) spectrum is very hostle place. Being able to pick out a signal mixed in with all the other signals, both natural and man made, is far more difficult than tuning in a cable TV station or processing a wired ethernet signal.

    For example, the WebGear Aviator wireless ethernet hardware (made by Raytheon) uses a 2.4GHz microwave "radio" to transmit a maximum of 1.5Mbps. The bit rate is over 100x slower than the transmitter signal rate. That's an amazing amount of "give" for interference given the relatively few devices "around the home" emmiting microwave freq. interference -- and no, your microwave oven isn't one of them; it's a slightly higher frequency centered on the molecular "vibration" of water molecules.
  • AM radio has been around for many years and why not. It has been a source of information or entertainment for as long. DSL is a new technology with a lot of promise in the future for high speed internet access for the masses. Claiming that DSL is an inferior standard because it interferes with technology that was designed prior to computers is premature and idealistic. How do we know that AM radio wasnt a bloated technology using more than its required airspace in frequencies. the truth is that there was not way to determine the future at the time that AM radio technology was developed. the truth is that You dont have to throw a rock very far to find other examples of things that will suffer as a result of interference from AM radio. On one side, AM radio has stood the test of time. FM has only partially been able to dethrone the technology that brought us those charming 50's tunes and early radio shows. People have been unwilling to give up this medium and nowadays it is more of a special interest tool than a widely accepted communication medium. On the other hand, DSL is a new medium technology with lots of promise in the future. the problem is that its only a stepping stone and other improved technologies based on it are already in the works. Just like anything on the internet, its life-line is likely to be 3 years or less when its replaced by the new and better thing. Im not advocating removing AM radio or DSL but, in the best interest of the future, shouldnt we re-examine the technology we use and make sure it is extensible enough to last into the future. Competing for frequency space wasnt an issue when there was no competition.. now that there is.. some implementation questions have to be asked. Its certainly than having interference with FM. wouldnt that be spiffy. LW
  • Umm, my message was not intended to be taken that seriously. I know you cannot feasibly do what I suggested.
  • Air planes are not Faraday cages. There two main reasons for not using cell phones in air planes. First, cell phones can emit a good bit of RF (usually in the mircowave range) that can interfere with the systems on the plane at such proximity. And second, once you're in the air, your phone can "see" dozens of towers and thus confuse the cell network -- plus, at cruise altitude (~35k ft) your phone will have to push out enough power to injure you.

    For the record, I've talked to people on cell phones during take-off. :-) (I;m surprised GTE didn't have a cow when that phone locked on every tower in the county.)
  • Pilots use AM radio to do adf navigation all the time. These stations are used to do non-precision approaches to airports. If this does interfere with AM radio stations, I can't beleive that the FAA has not done anything about it.

    I can just see the headlines..
    airplanes crashed because of Quake 3, news at 10.
  • I'm guessing (I am TOO tired to read the article and make total sense of it right now) that they have already isolated which frequencies effect ADSL. That leaves it to a simple matter of determining a way to filter out the noise from those frequencies at each end. That, unfortunately, is not easy.

    No. The primary way noise is compensated for is by sending *less* signal energy on frequency bands where the noise level is high (e.g. AM frequency bands), and *more* signal energy on bands where the noise is low.

    e.g. If you imagine a band pass channel which only passes frequencies between F-df to F+df, then you would want to send *all* your signal energy in that band (since the response of the channel elsewhere is 0!) So in general, the amount of signal you send on a particular band is something like (I'm not being precise here) proportional to the SNR in that band.

    So for the problem of AM intereference, they can simply elect not to send much signal energy in those bands, and this is already accounted for in the ADSL specs.

  • My cableco (optonline) has no caps on bandwith (up or down) and they also dont seem to give a shit what ports i listen on. I see 300+K/sec downloads. I once sent a ISO image to my friend that is on the same subnet as me and it went at over 600K/sec. The router (3Com/USR) could do the full 10Mbits...but ive never seen that. Plus i have a fixed IP. For $39.99 a month im happy with it
  • AM radio signals may be causing interference, but they're the ones licensed to be using the airspace. For crying out loud, what is going to be next? 'Basic laws of physics are making my network go slow'? If the technology is succeptable to AM interference, it is FLAWED, and the speed rating of the technology is dropped, and people have to DEAL WITH IT. It's not as if the bandwidth is necessary anyway, theres no way in hell ISPs are going to be able to handle hundreds of ADSL subscribers.. the subscribers are the ones with the cheap hardware and lines, the technology is fast but it sure as hell isnt stable (as demonstrated with this interference crap). The providers are the ones who need to roll out the huge cable backbones and stable systems. ISPs get a hell of a lot less bandwidth for their buck than subscribers. Not to mention the poor bastards who run webservers who once could serve thousands on their T3 connection, and now are paying for multiple DS3s to keep up. This technology should NEVER have been adopted by ISPs, and anyone who tells me that going higher than modem/ISDN for regular internet access was ever a good idea I consider to be the idiots who made the internet what it is right now... slow, unreliable, full of idiots with $25 a month cable pushing their entire CD collections to each other. RIP ADSL.
  • I live in Portland Maine, and we have RoadRunner (Time Warner Cable). I routinely get speeds of 250-300k/s to major sites...I've heard @Home is bad but I have not experienced such problems with RR...
  • Currently, the only ADSL provider here in Bangkok advertises the following MAXIMUM ul/dl rates:

    ...128/128...

    i reeled in horror the first time I saw the telco wiring here... unshielded and low quality cable is just the beginning. The price is paid in low low low ADSL rates, it seems.

    Moral: Those of you complaining you'll only get 1Mb dl speeds can still count yourselves luckier than those of us in the big mango.
  • And once again the benefits of AM stereo get ignored...

"An ounce of prevention is worth a ton of code." -- an anonymous programmer

Working...