Only one microfilter required?

[PeterRbg]

My Telkom copper line comes into my study/office, and from there it goes to quite a few other outlets around the house... Allowing me to move the phone around at will.

From a page on the Telkom web site and elsewhere, it appears I should be able to install a single microfilter in the study, downstream of the ADSL modem, thus providing a filter to all the house pots sockets.

Anyone got any experience or comments please?

 

[mas]

Hi PeterRbg
Heres a diagram of how your filter should be connected.

--Telkom Line
-------|-------
-------|-------
----SplitterCOLOR=White]---
---|-------|---
---|-------|---
-Filter---ADSL-
---|----Modem
---|
---|
---|
Analogue
Telephone/s

You can connect your ADSL Modem directly to your line, but your voice line should be connected to your filter.
So its either you connect a filter by every single port where you would plug your telephone or you can put the filter where your Telkom Line comes in (in your case your study/office) and just put your filter on that line. Does your filter have a built in splitter or is yours the one from telkom?

 

[PeterRbg]

Thanks for clarifying

Thanks for the response.

I assumed that the microfilter would simply be paralleled on the line, as is normal practice with mutliple handsets. So I will look to see if any filters actually contain anything more than this.... There was a comment somewhere that one should minimize T-junctions on telephone lines which are used for ADSL, so perhaps correct impedance matching is important.

On pctechguide.com I see the following: "a microfilter (also referred to as splitter) ...". And it shows some examples of what the devices look like.

This makes me think the "splitter" function is simply connecting the incoming line to an output connector for the ADSL modem/router, as well as via a filter to a standard telephone socket.

 

[sburrell]

A splitter and a micro-filter must not be confused. A splitter sits at the point the telkom line comes into your house and splits it into dsl and telephone cables. Microfilters sit at anypoint along the telephone line in your house to convert the digital stream into anolougye patterns.

 

[BTTB]

Good explanation Mas and Sburrell.

 

[PeterRbg]

More info on splitters

OK, I found the following on the Telkom web site:

"The DSL modem in turn is sensitive to changes in the condition of the line. For optimum results there must be no T-intersections (known as bridge taps in the industry). If additional wiring or devices are connected where the high frequency signals are present, the modem might not be able to decode the changed signals. There are two ITU-T standard solutions for this, G.992.1 and G.992.2. Telkom uses the G.992.1 standard. With G.992.1 both splitters or micro filters may be used. If a splitter is used it must be connected as the first device on the line from the exchange. It contains a filter that passes voice band, lower frequencies and direct current to a socket for the telephone, and a filter that passes high frequencies to a socket for the DSL modem. The micro filter option does not require the splitter. A high pass filter is built into the modem, and low pass filters (micro filters) must be used between any other device and the line. This is the preferred option due to simplicity and cost, without any penalties in performance."

This indicates that the splitter would solve my problem. Now, where to get one?

The page is http://www.telkom.co.za/athome/products/dsl/home_installations.html and provides two simple diagrams.

 

[stoke]

You may purchase a splitter at bleugh teklom bleugh offices.

 

[PeterRbg]

Not quite correct...

A splitter and a micro-filter must not be confused. A splitter sits at the point the telkom line comes into your house and splits it into dsl and telephone cables. Microfilters sit at anypoint along the telephone line in your house to convert the digital stream into anolougye patterns.

Microfilters are simply low-pass filters, which pass through voice, CLI and ring tones, but prevent the higher frequency ADSL (digital) data from entering the telephone/ fax/whatever. No conversion is done or indeed necessary.

 

[doobiwan]

Just to be pedantic, the lowpass filter does the opposite as well. It prevents High frequency noise from the POTS devices from interfereing with the High frequency signal of the ADSL device.

There's actually an ADSL Lite (g.lite) that doesn't require filters, I always wondered if that's what telkom is using.

 

[mas]

Thanks BTTB

yeah the splitter and filter are two different things.
But with my netgear modem which came with its own filter that had like a splitter built in. or a splitter with a filter built in.
The telkom ones are just the Filter alone, i dont know if they make the splitter+filter combo. it makes no difference tho!

 

[PeterRbg]

Final reply after installation etc

This is just to tidy up this thread with experience after installation...

My ADSL (192) service was installed by a subcontractor to Telkom. Very efficient, and replaced the cable from the street to bring it up to standard - round cable containing two twisted pairs.

The standard Telkom outlet was installed, which splits the signal in two directions. After he left I opened it up and found that it simply divides the circuit to two identical sockets, but does include a simple lightning arrestor between the two wires.

Also after the contractor completed his work, I re-installed completely as follows:

- Telkom line enters my study and connects only to splitter.
- One side I connected via a single filter back to the outside line which serves all the POTS outlets in the rest of the house, plus POTS outlets in my study.
- The other side connects directly to the ADSL modem - In my case I chose the Billion 5102 with 4-port switch
- I subsequently added an Ellies Wondertel Combo XHi, which provides surge protection on both the mains and the ADSL line.
- I retained my existing 56k modem to provide fax facilities. This connects to a POTS outlet and is also protected with a surge protector on both the power line and the telephone line.

After operating for a few weeks I can report that everything works correctly; no interference between ADSL and POTS services; data rates as expected whenever tested; and the 4-port switch works admirably for a mini home network.

Now, the only problem is one which may not affect many other people: I am also a radio amateur, and I now find I get interference approx. every 100kHz throughout the HF bands. This does not seem to be affected at all if I disconnect or even power down the ADSL modem, so not sure whether this is coming from the ADSL line, or if it is something else that started up about the same time....