ADSL filters and line splitters are a surprisingly common point of failure for home broadband connections. These seemingly innocuous little devices separate the low-end frequencies required for voice calls from the high-end frequencies needed for your ADSL connection. However, the poorly made freebies dished out by some ISPs are prone to fail, leading to excessive noise interfering with the speed of your connection.
In addition, filters that are adequate for ADSL may not be optimal for ADSL2/2+ – a spokesperson for Netcomm told us that you may get only two thirds of your possible speed. Ditch any old filters you have and buy new ones that meet the ADSL2+ standard – look for AS/ACIF S041:2005 and Telstra RCIT-0004 certification on the packaging.
But before you pop down to Officeworks and buy a job lot of filters, there are a few basic checks to perform first. Make sure there’s a filter fitted to every socket in the house where there’s telephony equipment attached – be that the telephone in the back bedroom, the Foxtel box or a fax machine.
The filter should plug directly into the wall socket. If you have a two-way splitter coming off the wall socket (to serve a phone and a fax machine, for example), make sure the filter is plugged in before the splitter.
A tell-tale sign that one of your filters has gone wonky is noise on the line when you’re making voice calls. Zen Internet provides a comprehensive guide to testing your ADSL filters at www.pcauthority.com.au/links/129broad2, but it essentially involves plugging each filter into your boundary termination socket in turn to eliminate the faulty unit.
If you’ve ever wondered what the inside of an ADSL microfilter looks like and why some are better than others, the UK-based ADSL nation website provides a terrifyingly detailed example, and while there’s no Australian site evaluating filters, Whirlpool’s filter recommendations are a good place to start.
Alternatively, you could invest in a central splitter. This is usually done when all other methods of getting a reliable ADSL connection have failed, and involves paying a technician around $150 to install a splitter on the telephone line before the first phone point in the property.
A central splitter means that you don’t need filters for phone lines in your house, but your ADSL modem can only be connected to the specific phone point created at the central splitter for the ADSL modem.
WATCH OUT FOR AR7 ROUTERS
Can’t understand why your ADSL line doesn’t hold a connection? Don’t worry, neither could thousands of others until diligent work by an ISP technical support team discovered a fault with the Texas Instruments’ AR7 chipset, found in many brands of ADSL router.
In short, the AR7 routers were found to be the common factor among customers who reported that their connection kept dropping every few minutes, making video streaming and online gaming nigh-on impossible. It seems the chipset has a problem dealing with electrical noise on the line.
The AR7 isn’t ADSL2+, so if your high speed broadband connection works, it’s unlikely you have to consider the AR7 as a possible speed hurdle.
Finding out whether your router contains the AR7 chipset is no picnic. Router manufacturers often neglect to specify which chipset is built into their equipment. You’ll find a list of some of the models containing the AR7 chipset at www.linux-mips.org/wiki/AR7
Does this mean you should throw out your AR7-based equipment? Not necessarily. Some manufacturers, such as Netgear, have released firmware updates that have reportedly solved the problem. Check your router’s software interface to see if there are any firmware upgrades available for your model.
If that fails, borrow a non-AR7 router to see if that improves the reliability of your connection, before investing in new equipment.
How to measure your broadband speed
Determining the true speed of your internet connection isn’t as easy as you may think. There are several, often contradictory, measures of your ADSL connection speed. These include:
Sync speed (or line rate)
This is the speed at which your router connects to the local telephone exchange – the theoretical maximum speed your line could achieve in perfect conditions with a following wind and a deadly virus wiping out your entire neighbourhood. This is the figure that pops up in the little bubble in the Windows System Tray when you first connect to your router.
Attenuation and noise
Attenuation and noise regulate the maximum throughput you’ll receive on your connection. Attenuation is a measure of how much signal is lost through your connection.
Line attenuation is a measure of how healthy the wiring is, and Telstra can perform a signal qualification test that should give you some idea of what speeds you can expect.
Signal attenuation is about the quality of connection through your modem, and it changes constantly. Noise is generated by electrical interference, whether from telephony devices or other causes.
The ratio of signal to noise (SNR) determines ADSL sync speeds. SNR margins are set at the DSLAM, and only your ISP can adjust them.
This is the “true” speed of your connection – taken by measuring the actual rate at which data is downloaded and uploaded. Naturally, this is slower than the sync rate and often well below the mythical ‘up to 24Mb/s’.
Sites such as www.speedtest.net will accurately determine your actual throughput. If you’re running your router off an extension socket, try performing a speed test and then connect your router to the house’s master socket and run the speed test again to see how much speed you’re losing.
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Interested in Naked DSL? Also see our Naked DSL Buyer's Guide