Can Phone Extension Leads / Cords affect ADSL2+ Speed?

You may be familiar with this scenario.

You move into an older style apartment or house, and the phone socket is in the most inconvenient place - like in a hallway, or on a wall where there isn't a power point!. So you head down to the $2 shop and get a few 10-metre phone extension leads (or extension cords), run them along the floor and sticky tape them around the doors and windows to where your PC is, and set up your modem there. Looks tidy, and works fine for now...

What you may not realise is those extra few metres of cheap, thin, unshielded cable is slowing your ADSL2+ internet speed - and you will really notice it the further you live from the exchange!

OK for Phones, Bad for Modems

Those flat ribbon-style phone extension leads are made of really thin multi-strand wire (to keep them nice and flexible). If its a standard two or three metre cable, the effect is negligible. But if your using a 10 metre cable (or heaven forbid you have more than one 10m extension lead daisy chained together!) then the increased impedance in the cable (proportional to cable length and inversely proportional to the conductor's cross sectional area) will cause your signal to drop, and you'll lose speed. To be more precise, you'll lose bandwidth, which affects your overall throughput.

Impedance (a close friend of "resistance") of the cable is not the only downside. Phone extension leads are unshielded, which means the longer they are, the more likely they are to pick up stray EMF (electro-magnetic frequency) signals coming from your microwave, your old CRT TV set, your mobile phone, the local radio station's tower, and much more. A better way to say it is that your long extension lead acts like a big antenna! All these stray signals are absorbed by your phone cable, and cause high frequency noise on the line, which your modem hates. Again, this affects your bandwidth, as the modem won't be able to use all available "channels" if the signal to noise ratio is too low, which affects your overall sync (and available upload/download) speed.

And if you have an old phone extension cable lying around that your grandma used back in the day, forget it! Like any metal, the conductors inside these 'flexible' cables eventually fatigue and break due to continual bending (termed "cyclic loading"). This is why running extension leads under the carpet across walkways isn't a good idea; as the cable is continually walked on, over time it fatigues and begins to fail. The tiny strands of metal conductor inside the cable break, increasing your line's impedance, and in most cases actually causing high frequency noise on the line.

What are the solutions

The first option is to go wireless for both your phone AND your internet. If you have power near your out-of-place phone socket, just whack in a cordless phone base-station there and a wireless modem/router. Most cordless phones these days come with two handsets, a base station, and a standalone charging base, so all you need to do is set up the second handset (with the standalone charging base) in a more convenient location, like in your bedroom, or next to the couch. Then just configure your wireless network on your PC (you may have to purchase some extra hardware, like a small USB wireless network dongle). This solution keeps the phone cable under 3 metres, but may not be a good solution if your place is double-brick and your PC is fairly far from your modem (unless you add a few Wireless Repeaters around the place). Most homes and businesses should have this in place already for the growing popularity of mobile devices (like tablets and smartphones).

The second option (preferred) is to get a licenced technician to install a "Cat 6" network outlet (or "RJ45 data socket") next to your phone socket (which is where you'll plug in the modem) and another one in your preferred place (i.e. where your PC, TV, and/or Xbox is). This way, you'll have a hard wired connection between your modem and PC - secure & fast - keeping your phone cable nice and short, under 3m. Due to the way Cat 6 network cable is designed (and the way Ethernet works), it isn't affected by EMF as much as those pesky ribbon-style phone extension leads.

Another solution is to get a phone technician to install a new phone socket in the room you want your modem to be. The proper phone cable to use inside homes and businesses is of higher quality than cheap extension leads. The conductor is much thicker (and not multi strand; its solid core) and the wires are twisted in a special way to reduce the effects of EMF. This solution however still extends the overall length of the phone line, which still lowers your ADSL2+ bandwidth (upload & download speeds).

And lastly, the easiest solution and possibly the cheapest we can recommend is to extend the data cable instead of extending the phone cable. Rather than extending your phone line to another room and having your modem next to your PC, keep your modem close to the phone socket and use a long Patch Lead / Ethernet Cable from your modem to your PC, laptop, xBox, TV, etc. Again, the ethernet cable is affected much less by EMF than the phone cable.


Please keep in mind that if you really need to extend the position of your ADSL modem, you'd want to keep the phone line as short as possible, and away from power leads or magnetically-noisy devices. If you live in the Sydney metro area, contact Cabled After Hours today to get a quote for a phone socket relocated or new data cabling installed in your home or office!

Scarnon Cabling Solutions has taken over "Cabled After Hours"


© 2020 All Rights Reserved – Scarnon Cabling Solutions – ABN: 92 619 708 137 – Privacy Policy