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alarmfilter

@ovh.net

Difference between a DSL filter and an ADSL2+ filter?

is there a difference between a dsl filter and an adsl2+ filter (for an alarm system)? if so, is the difference significant?



leibold
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Both DSL (ADSL1) and ADSL2+ filters are low-pass filters designed to block anything that is higher then the frequencies used for analog voice on the phone network. This means that the filter frequency is the same (somewhere between 5 and 25kHz)!

However the highest frequency used in DSL (ADSL1) is only 1.1 MHz while in ADSL2+ the highest frequency is twice as high at 2.2 MHz. This means that older DSL (ADSL1) filters were not designed for or tested with frequencies above 1.1MHz and they may present an undesirable load at those higher frequencies (then again, they may not!).
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public

join:2002-01-19
Santa Clara, CA

1 recommendation

reply to alarmfilter

said by alarmfilter :

is there a difference between a dsl filter and an adsl2+ filter (for an alarm system)? if so, is the difference significant?

You should never use an alarm filter with adsl2+. Use NID splitter instead.

TheMG
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Canada
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1 recommendation

Yes, use an ADSL2 "POTS splitter" and home run to DSL modem. It's the best way to go.



toby
Troy Mcclure

join:2001-11-13
Seattle, WA
reply to alarmfilter

For an alarm system you need one of these.
»www.amazon.com/Excelsus-Z-Blocke···00B912RK


lutful
... of ideas
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Ottawa, ON
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This type of filter is designed to seize the phone line during alarms. Separate DSL filter would still be needed for the phone/fax.


tschmidt
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2 edits

2 recommendations

reply to alarmfilter

I think this thread, is conflating different things.

ADSL2 vs ADSL2+

The OP was asking about the difference between filters for ADSL and ADSL2+. As leibold See Profile posted ADSL2+ uses frequencies up to 2.2MHz whereas ADSL and ADSL2 only go to 1.1. So all else being equal customer should get a splitter rated for ADSL2+. Having said that from other discussions I've had about this topic regular filters are pretty much a brick wall at 2.2MHz. So even if they are not specifically rated for ADSL2+ they work just fine.

ALARM

Now on to the Alarm issue. The easiest thing to do is to install a while house splitter at the NID and install a home run from the "data" side to a "data" jack at the modem location. Then run the splitter "voice" side to the RJ31/38 alarm jack, and from the alarm jack to all the non-DSL devices in the house.

In that case as far as the alarm is concerned there is no DSL. The down side of this arrangement is if someone decides to plug in a phone instead of the DSL modem into the data jack and the phone is in use the alarm will not be able to disconnect it to make the emergency call.

I find lutful See Profile drawing confusing. I think I figured out what it is trying to say. The alarm is placed first in line so it is able to disconnect a call in process to make the alarm call. The reason for using a alarm filter is because the alarm does not have ADSL protection built in.

If the alarm does not have built in DSL low pass filter you need to add one and the only place to do that is between the alarm jack and the alarm. Adding an external low pass filter there protects the alarm from DSL. However that will also prevent high frequencies used by DSL from getting to the modem so there is also a high pass filter to pass DSL frequencies to the modem. Not sure what the the purpose is of the right hand low-pass filter, unless there is a concern the modem DAA passthrough relay might degrade DSL so to play it safe and make sure DSL tones are not feed back to the DAA.

Assuming you are close to the CO and signal is strong should work fine but if DSL is marginal that arrangement will probably degrade DSL to some extent. A direct connection to the DSL modem is better as long as you make sure a phone is not connected in place of the modem

Hopefully that helps rather than make this topic even more confusing.

/tom
fixed typos - expanded alarm stuff



alarmfilter

@ipredator.se

thanks for all your input! believe me when i say that every post here has been helpful in its own way.

i was hoping there was some kind of standard that would enable manufacturers of alarm filters to indicate that their filter was certified to work w/ either dsl1 or adsl2, but since i haven't found any filters explicitly claiming adsl2 compatibility, i suppose i will have to be content with any filter as long as it does its job.

i am aware that using a pots splitter is the better option, but drilling through multiple floors (and possibly walls) would require considerable money that i don't have, so i decided to filter the signal instead. probably not perfect, but i was hoping it would get the job done at a fraction of the cost.

and finally, thanks for summing everything up so nicely tschmidt.


lutful
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said by alarmfilter :

i was hoping there was some kind of standard that would enable manufacturers of alarm filters to indicate that their filter was certified to work w/ either dsl1 or adsl2, but since i haven't found any filters explicitly claiming adsl2 compatibility,

The block diagram of a standard RJ31X alarm filter imply that it will be fine for all variations of DSL because it does not actually cut off the higher frequencies to the RJ11 output port.

»www.security.honeywell.com/docum···adsl.pdf


tschmidt
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reply to alarmfilter

said by alarmfilter :

i was hoping there was some kind of standard that would enable manufacturers of alarm filters to indicate that their filter was certified to work w/ either dsl1 or adsl2,

From a filter perspective there is no difference between ADSL and ADSL2, both use frequencies up to 1.1MHz.

ADSL2+ doubles maximum speed over short phone lines by increasing upper frequency bound to 2.2 MHz.

Marketing 101: if filter literature just says DSL it was designed to 1.1MHz upper limit, if it say ADSL2+ designed and tested to 2.2.

On the wiring front it may not be absolutely necessary to pull more cable to use a whole house splitter. All depends on how you residence is wired. If inside wiring is at least two pair and you only have one phone line you can install a whole house splitter ahead of the alarm and use the spare pair to connect the DSL modem. Ideally inside wiring should be twisted pair but even old style quad-four should be fine as long as it is not too long.

Prior to the mid-1980s residential phone wiring was installed as a daisy-chain. Cable looped from one telephone jack to the next. Now a days phone wiring is installed as a home run, just like Ethernet. Wiring for each jack converges on a central location. Home run is better for DSL since only the jack near the modem needs to be connected, reducing losses.

/tom

lutful
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said by tschmidt:

On the wiring front it may not be absolutely necessary to pull more cable to use a whole house splitter. All depends on how you residence is wired.

Let's assume OP will choose NID splitter route ... he will have to locate every phone/fax in the house after the alarm filter. Otherwise the alarm panel will not be able to seize the POTS line.

public

join:2002-01-19
Santa Clara, CA

said by lutful:

Let's assume OP will choose NID splitter route ... he will have to locate every phone/fax in the house after the alarm filter. Otherwise the alarm panel will not be able to seize the POTS line.

Why?
The alarm filter is redundant in the above picture.
Leave phones and alarm as is. Just add a splitter and a new cable to the modem. In an old house the modem needs it anyway.


tschmidt
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said by public:

Why?

I assume lutful See Profile meant alarm jack not alarm filter.

/tom

lutful
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Ottawa, ON
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1 edit
reply to public

said by public:

said by lutful:

Let's assume OP will choose NID splitter route ... he will have to locate every phone/fax in the house after the alarm filter. Otherwise the alarm panel will not be able to seize the POTS line.

Why?
The alarm filter is redundant in the above picture.

public See Profile and tschmidt See Profile ... kindly read that Honeywell document link I posted earlier. A monitored alarm panel must be able to sieze the POTS line when it is trying to communicate an alarm condition.

That feat is quite impossible without a certified alarm filter shown as the "RJ31X" block below the alarm panel in above diagram. P.S. My mistake - the clever design of the RJ31X jack does this function without any electronics.


tschmidt
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said by lutful:

That feat is quite impossible without a certified alarm filter shown as the "RJ31X" block below the alarm panel in above diagram.

Why? If the user places a whole house POTS/DSL splitter between the NID and the Alarm jack the alarm does not see the high frequencies used by DSL so there is no need to use a DSL filter at the alarm or other at non-DSL device.

I agree with you that if the installation does not use a whole house splitter ahead of the alarm then the alarm needs a filter.

ADSL modems do not draw loop current so have no effect on alarm seizing the line.

To be clear when I say a whole house POTS/DSL splitter this is what I'm discussing. This is a multistage passive low pass filter that prevents high frequency DSL signals from interfering with low frequency POTS network.

»tiinetworktechnologies.com/repos···0108.pdf

/tom

lutful
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2 edits

OK, I see your point now.

However, if there is ever any problems with alarm monitoring, the insurance company may take notice of the omission of the alarm filter.



leibold
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reply to lutful

said by lutful:

public See Profile and tschmidt See Profile ... kindly read that Honeywell document link I posted earlier.

That documentation is showing alarm system integration with and without POTS splitter. It doesn't mention RJ31X/Alarm dsl filters for which is the only flaw of an otherwise well done document.

In the "Split Installation" (which even Honeywell seems to favor) an Alarm DSL filter is simply not necessary.

In the "Splitterless Installation" an Alarm DSL filter is not shown in the Honeywell document, but it would be recommended to:
- prevent too much degradation of the DSL signal being routed through the alarm system.
- prevent DSL signals from interfering with the operation of the alarm system (see the comments specific to the FBII panel).

Edit: I'm not a fan of alarm system DSL filters. There is an (admittedly short) cable from the filter to the RJ31X jack where the same DSL signal travels in opposite directions allowing for synchronous but phase shifted interference with itself (might not be an issue, but certainly not falling into the category of best practices). Depending on the quality of the high-pass and low-pass filters and their filter frequencies there is additional interference possibility especially from signals close to the filter frequency (that may pass through the high-pass filter as well as time delayed through the low-pass filters).
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lutful
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Sorry, my earlier comments reflect a misunderstanding of where the POTS line seizure took place. Since the RJ31X jack itself does that job, there is no need for the alarm filter with a NID splitter.

»Help with home alarm system hookup.