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Wannabe Geek


Topic # 11194 9-Jan-2007 00:57
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Hello everyone,

I am a dewy eyed broadband virgin, sighing gustily at the prospect of imminent connection at the house we have just bought.  Hold on, I have to choose a "connection method".  If we have monitored alarm or more than 5 jackpoints then a techie needs to install a splitter apparently.  The house has more than 5 jacks and has an alarm (tho not currently monitored).  I know the previous people were on broadband but i dont know if they had a splitter installed, and telecom cant seem to be able to tell me.  How do you tell if the house has a splitter already?  Will I have to pay $150 for some guy to come and say "Its already there dummy"?  I understand the splitter is at the termination point - is this in the house or outside? The house does not have aerial wires, its all underground.  None of the house jacks look profoundly technical.

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  Reply # 57285 9-Jan-2007 05:29
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jimmythegeek: How do you tell if the house has a splitter already?...None of the house jacks look profoundly technical.

There are two easy clues:

1)  Is there a separate jackpoint for the ADSL modem?
2)  Does one of the jackpoints have a larger than usual white box on the wall?


Either of these things will normally indicate that a splitter has been installed.

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  Reply # 57286 9-Jan-2007 05:57
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Even if you have more than 5 jacks, but not that many phones, I'd say go for a self install (with filters). If it doesn't work, you can always get a splitter installed later, and it might save you $150. :)

BTW, if you do end up installing a splitter now, they won't charge you $150 unless they actually install it. Although, I'm not sure if they'll charge a call-out fee or something similar, best to check with your ISP (or Telecom).

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  Reply # 57300 9-Jan-2007 09:14
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willnz: Even if you have more than 5 jacks, but not that many phones, I'd say go for a self install (with filters).

The only problem with that strategy is the presence of an alarm.  Monitored or otherwise, it doesn't make much difference:

Alarms are generally hard-wired into the phone line (rather than going via a jackpoint) to prevent tampering.

The hard-wired connection necessitates a splitter rather than a plug-in filter.

As I have posted previously, the splitters are around $80 from MasterTrade and not at all difficult to install so long as you can do basic telephone wiring.  There are only 4 connections, so it's not really that complicated.

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  Reply # 57327 9-Jan-2007 13:51
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Another thing is that the 5 jackpoints refers to how many are actually in use. If you have 5 jackpoits but only 2 phones and say Sky Digi (uses a jackpoint for betting and pay per view) then your fins as you've only used 3 devices.

The reason they look at this is each electrical device plugged into your wiring system adds a certain amount of interference or noise on the line. This in turn interferes (sometimes only marginally) with the broadband signal as the only thing differentiating incomming data as voice or internet is the frequency at which it's sent, hence being able to use the phone and the net at the same time.

So if look at how many devices you plug into your phone jacks not how many jacks you have.

Another quick test is to check all of your jackpoints by plugging in a corded phone into each one. If you find one that doesn't have a dial-tone then its quite possibly a jack that has a splitter attached.

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  Reply # 57330 9-Jan-2007 14:15
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SilentOne: The reason they look at this is each electrical device plugged into your wiring system adds a certain amount of interference or noise on the line.

Actually, it's known in the trade as "loading" or REN.  The ringer in each phone has a certain impedance and the more phones you have across the line, the lower the impedance becomes which will eventually stop the ADSL signal working at all unless you have a filter at each jackpoint which is in use.

SilentOne: Another quick test is to check all of your jackpoints by plugging in a corded phone into each one. If you find one that doesn't have a dial-tone then its quite possibly a jack that has a splitter attached.

Actually, that's not correct.  If you plug a standard phone into the "ADSL" socket (which comes off before the splitter), you will get dial tone, just the same as normal.  However, depending on the phone, you will probably also notice a "hissing" sound, which is the ADSL signal.

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  Reply # 57332 9-Jan-2007 14:56
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Actually, that's not correct. If you plug a standard phone into the "ADSL" socket (which comes off before the splitter), you will get dial tone, just the same as normal. However, depending on the phone, you will probably also notice a "hissing" sound, which is the ADSL signal.


Oh, you learn something new everyday. That's how I found the ADSL jack in my house as it wasn't labelled. It was the only jack point that I couldn't get a dialtone on but ADSL still worked... any ideas why that would be?

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  Reply # 57336 9-Jan-2007 15:13
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SilentOne: ...It was the only jack point that I couldn't get a dialtone on but ADSL still worked... any ideas why that would be?

It could be that whoever wired the jackpoint used different pins than the normal ones (2 + 5).  In which case when plugging in a standard phone you wouldn't hear anything, but by using the corresponding BT to RJ11 adapter wired for say pins 1 + 6 it would allow the ADSL to work.

Just a theory, but I think it's the most likely explanation.

So far as I remember, the ADSL jacks at the 3 different installations I have been involved with all used pins 2 + 5, but some other installation companies may do it differently.

Someone else with wider Telecom experience can probably offer a further explanation.

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  Reply # 57403 9-Jan-2007 21:00
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Wicked, cheers for the explanation.. will remember that for next time I'm in a new house... save on a splitter install :)

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  Reply # 57430 10-Jan-2007 07:04
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The adsl filter provides two functions, firstly its a low pass filter to keep the adsl signal out of your pots devices, if you listen carefully you sometimes can hear it, if only faintly even with the filter installed.

Secondly the filter is designed as an asymetric design, so from the line side it consists of a series common mode inductor followed by a shunt capacitor and then terminated with pots devices. This design ensures that whatever impedance the pots devices present to the pots side line at adsl frequencies they do not load the adsl signal. Most pots devices will present a quite low impedance at frequencies above the voice band to filter any noise, if this was put directly on the adsl line, even when on hook, it would disrupt or attenuate the adsl signal, thus the filter ensures that this low impedance is lifted. However more than five filters across the line will start to present its own loading problem, thus no more than five is recommended.

As I have mentioned before, you can buy a high quality filter from mastertrade made by marque magnetics ($50 trade, $75-80retail) and seperate the adsl and pots circuits at the line entry point, or you can modify a standard microfilter ($10-15) to do the same job, in most domestic installs this will work just fine and ensures all pots jacks are protected and can allow a stub free wiring layout that further insures optimal performance.

Cyril

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  Reply # 57439 10-Jan-2007 09:58
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Cheers Cyril for that very complete and well explained description of the innards of an ADSL filter.  I knew they were low-pass but wasn't aware of the "Common Mode" inductors at the front end.  Keeping the impedance high to ADSL frequencies is vital or else what little signal there is (by the time the line attenuation has taken its toll) will be squandered.

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