I thought DSL modems didn't work through filters

Discussion in 'OT Technology' started by mdaniel, Apr 20, 2007.

  1. mdaniel

    mdaniel S is for Shiksa

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    I was at someone's house today and saw that their DSL modem was synced at 400k/160k. I had a look around to make sure that all of the phones were filtered when I discovered that she had a filter on the main phone jack in the house off of which everything else, including the modem, branched. I removed that filter and filtered a branch with a phone on it, and the modem's downstream synced at 860k. I always thought that DSL filters would block the modem from syncing at all. I've never actually tested it though.
     
  2. D3aC0n

    D3aC0n Vesa ToskaLOL OT Supporter

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    that's because the DSL line in that particular house is close enough to the CO so that the signal strength is actually strong enough to sync with the modem, even though a filter is in place. But yeah.. in most situations, a filtered DSL modem won't sync
     
  3. P07r0457

    P07r0457 New Member

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    I have seen filtered dsl modems sync intermittently. They sync and lose sync repeatedly. A filter is just a low-pass filter... There is a gradual curve, so some dsl signal in the lower frequency band will pass through. DSL generally uses DTM which is fairly robust in it's ability to adapt to line conditions -- effective sacrificing throughput for link quality.
     

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