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AM Frequency Hinders ADSL Capacity

Posted by ryuzaki0 on from the so-much-for-talk-radio dept.

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. "

9 of 124 comments (clear)

  1. Re:FCC rules by turg · · Score: 3
    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

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  2. AM interference should be accounted for by gargle · · Score: 3

    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.

    1. Re:AM interference should be accounted for by RISCy+Business · · Score: 3

      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.

      --
      your company here.
      shelby != ford
  3. A link with more detail . . . by layne · · Score: 3

    I remember this mention in a study done by avalon.net two years ago. This piece 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.

  4. Amateur Radio is also affected. by Rick+Evans · · Score: 3

    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

    1. Re:Amateur Radio is also affected. by revnight · · Score: 3

      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

      --
      "The things we wizards have to put up with."--Jethro Bodine
    2. Re:Amateur Radio is also affected. by revnight · · Score: 3

      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

      --
      "The things we wizards have to put up with."--Jethro Bodine
  5. Lotta greedy bastards here... by Wakko+Warner · · Score: 4
    "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

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    "Remember when the U.S. had a drug problem, and then we declared a War On Drugs, and now you can't buy drugs anymore?"
  6. Why, AM radio, of course. by Wakko+Warner · · Score: 3
    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

    --
    "Remember when the U.S. had a drug problem, and then we declared a War On Drugs, and now you can't buy drugs anymore?"