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Author Topic: Filtered DSL over standard phone extension cable?  (Read 3688 times)

burakkucat

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Re: Filtered DSL over standard phone extension cable?
« Reply #15 on: August 20, 2019, 10:03:38 PM »

Thank you. All understood.  :)
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chazzo

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Re: Filtered DSL over standard phone extension cable?
« Reply #16 on: August 21, 2019, 12:34:08 PM »

Well, thank you. And everyone else who has taken the time to post. Itís really much appreciated.
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burakkucat

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Re: Filtered DSL over standard phone extension cable?
« Reply #17 on: August 21, 2019, 02:58:14 PM »

Well, thank you. And everyone else who has taken the time to post. Itís really much appreciated.

b*cat blushes as he performs one of his Japanese-style bows.  :blush:
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Alex Atkin UK

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Re: Filtered DSL over standard phone extension cable?
« Reply #18 on: August 25, 2019, 02:01:38 AM »

Pretty sure my main line is the old ADSL Nation (marked as ADSL 1.0), it performs no different to any of the dangling microfilters supposedly designed for VDSL in my experience.  Although to be fair, I don't have bridge taps, just a single extension leading to the DECT base station so that it not right next to the modem.

My second line I think has the Mk3, the first line has better stats although they are both syncing the same lately.
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chazzo

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Re: Filtered DSL over standard phone extension cable?
« Reply #19 on: August 25, 2019, 12:36:18 PM »

Pretty sure my main line is the old ADSL Nation (marked as ADSL 1.0), it performs no different to any of the dangling microfilters supposedly designed for VDSL in my experience.

Interesting but perhaps not surprising? The ADSLNation filter was supposed to be one of the best in its day, wasn't it? And I have the (uninformed) impression that dangling filters range from good to poor, at least in theoretical terms. I've no idea whether changing filters makes much difference in practice, and if it does, which design works best will probably depend on the line. This post from 2012 compares the ADSLNation with presumably the BT Mk3 SSFP and found no difference in sync speed.

I don't even know how or why the filter affects the DSL signal. I presume the input stage of the modem ignores anything at speech frequencies, so we're only concerned with how it might muddle or attenuate the RF. A quick search of Google Scholar turns up some references to active filters (ass opposed to active components), which I guess could  be the future Ė unless we just give up on wired telephony altogether.

I had a quick look inside a Mk3 and it looks quite similar to the Mk4, with four large inductors. Bcat suggested they may be identical.
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Weaver

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Re: Filtered DSL over standard phone extension cable?
« Reply #20 on: October 14, 2019, 06:35:59 AM »

The excellent ADSL nation active filters cope better when there are many devices plugged in to the phone line or awkward devices with unusual impedance. The active design is more sophisticated in order to cope better with the different requirements of the on-hook vis off-hook situation. If you have a single Ďnormalí phone or no phone at all then you wonít see an improvement from an active type filter. I have seen very slightly better performance from a passive BT Pressac type filter but almost non existent, in the limits of what can reliably be measured only after many tests. For an explanation of the design rationale see the textbook by Golden and Dedieu - I think itís the second volume which has a chapter on filter design. One of the authors worked on the only other active filter Iím aware of, made by a French company whose name escapes me.

If you have a situation where DSL performance goes bad while a telephone call is in progress, then you need a better filter, or even better a better filter and dump the telephone which is causing problems in favour of a different model, or get rid of telephones altogether.
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