Cascading ADSL Filters

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pm

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#12150 1-Mar-2007 19:05

I constantly hear the fact that ADSL filters (like the standard DLink/DSE ones) we use in our homes are absolutely crap.
Now, I want too know whether cascading mutliple ADSL filters one after the other will make it "less-crap".

Are these filters "low-pass" / "band-pass" / "high-pass" or "notch" filters? If so I'm assuming they're passive. I do know that active filters are improved by cascading more...

grant_k

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#62471 1-Mar-2007 19:19

pm: Now, I want too know whether cascading mutliple ADSL filters one after the other will make it "less-crap".

That's a bad idea...

All you will accomplish is to increase the losses between your phone line and the output of the second (or subsequent) filter, which I am assuming would be connected to a phone or fax machine. Consequently there will be a loss in volume of the audio signals in the phone's earpiece, and the caller will also hear the signal from your microphone at reduced volume.

pm: Are these filters "low-pass" / "band-pass" / "high-pass" or "notch" filters? If so I'm assuming they're passive. I do know that active filters are improved by cascading more...

They are a passive low-pass filter. Unlike some active filters (by no means all, I might add) you will not improve things by cascading them.

If you really want to do things properly, get hold of a hard-wired splitter from MasterTrade for around $75 to $80 retail. If you have a trade account it will cost you a bit less.

cyril7

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#62474 1-Mar-2007 19:50

To concur with Grant the filters are low pass, and of an asymetric impedance design. Along with reducing ADSL energy (ie above speech band) their primary purpose is to ensure that the impedance presented by any filtered device (on the phone side) does not load the incoming line and thus affect ADSL performance.

By and large the basic micro filters are perfectly adequate even if you used one to filter your entire home phone connections. If you want to ensure best performance go to master trade and get a Marc Magnetics MM3200 filter, these have a full trade price of around $75 but depending on what levels of discount your presence at mastertrade can muster they can be got for as little as $45. The MM3200 is the only Telecom approved filter as used by Telecom techs in full single filter installs. These filters are a 6pole design as opposed to the 2pole design that micro filters are.

Surpisingly the extra poles dont seem to assist ADSL performance unless you are working on a marginal line, but do help suppress adsl junk getting into your phones better than basic micro filters.

End story is that unless you have marginal ADSL service (ie 4km or more from exchange) you will most likely not acheive alot by installing a top of the line filter. But peace of mind is a wonderful thing.

Also concatenating them will not assist ADSL performance due to the asymetic nature, however it may help further reduce ADSL junk in your phone circuits, ie dont bother.

Cyril

richms

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#62514 1-Mar-2007 23:45

Some filters only have one inductive element in them. I cascaded 2 dse filters and it fixed the problem where a long cable on the output would mess up the adsl on the line. I had to make sure there was a polarity reversal between the 2, but chopping the BT plug off and re crimping it solved that.

Richard rich.ms

cyril7

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#62543 2-Mar-2007 06:55

Sure it may work, but stacking two poles and stops directly on top of one another is mostly likely to produce a rough filter response. Further, most micro filters are only just capable of satifying the DC loss requirements, cascading two may not result in an ideal outcome in this respect.

Cyril