Westell modem interfering with voice

[jfcl]

I have installed ADSL (Verizon DSL with Westell 2200 modem) at our church. I used the standard basic installation technique: DSL filters on the phones, and the modem in one of the phone taps without a filter.

The DSL service seems to be fine-- I haven't checked the throughput but from browsing it seems sufficient if not good.

Voice still works fine also, with one exception: When I take the phone off-hook to place a call or answer a call, I occaisionally get a load hissing on the line. The hissing is apparently coming from the DSL modem since it goes away when I unplug the DSL modem from its phone jack.

The hissing sounds like what you'd hear with a 56K modem on the line. It's definitely too low frequency to be stripped by the DSL filters.

Question: does DSL use the voice band for additional bandwidth when the voice phone is on-hook?

We do have an alarm system in the building. The phone line is wired through the alarm system. I know that's not a good idea for DSL, but it does (almost) work.

Current configuration:

NID-->Alarm---->DSLmodem
             \
              \-->DSLfilter-->VoicePhone

I did test the DSL modem directly at the NID:

NID---->DSLmodem
     \
      \-->DSLfilter-->VoicePhone

annd I could not reproduce the hissing problem. However, once I connected the alarm (and the rest of the building wiring) the problem came back, even though the DSL modem was connected directly at the NID:

NID---->Alarm---->(other phones with filters)
     \
      \-->DSLmodem
       \
        \-->DSLfilter-->VoicePhone

Question: Would the following configuration help with this problem?

NID---->DSLfilter-->Alarm---->VoicePhone(s)
     \
      \-->DSLmodem

Question: Is this possibly a defective modem?

Thanks!

 

[allteltec]

You need to filter all Phone devices that incluces alarm systems. You a lucky that DSL works though the alarms system. I have never seen one that did.

 

[exverizon]

There's special alarm filters that are SUPPOSED to work with DSL, but I wouldn't bet the rent. I always split off DSL on its own pair at the NID, or at least before any stations, unless there's no spare pair available. That way, there's no possible crashes. And I'm not a fan of those 2Wire brand filters anyhow; I don't seem to have much luck getting clean DSL performance as when I place a Keptel splitter in the mix. They work.

 

[dhnl]

Use something like this.

http://www.wilcominc.com/products_splitters_PS15.cfm

Connect CO Line to Splitter/Filter to ADSL Modem and
Splitter/Filter to Analog Phones via Alarm RJ31X Jack

 

[jfcl]

Here's an update: I rewired the phone line as in the last diagram, with the DSL modem first and a DSL filter before the alarm. This has eliminated the problem with hissing when the phone is taken off-hook.

I did use one of the 2Wire micro-filters that came with the DSL modem. Probably not the best, but certainly workable.

I still am curious about one thing, which no-one seemed to address: does DSL use the voice band for additional bandwidth when the voice phone is on-hook?

Thanks for all the useful comments!
--jfcl