Phone and Fax on same line? Problems

reidyg

We have an eircom broadband bundle at home. Until recently we've been able to use the phone and fax on the same number/line. The fax line comes from the phone/broadband socket and had gone through the modem of the computer to the fax/printer. The phone itself is in another room. However, after a computer repair to the power supply, it came back without the modem, which I will chase after. Since then calls cannot be received/dialled from the phone as the fax is plugged straight in to the wall. Faxes can be sent. I know this sounds very confusing, but surely there is a way around this without having to connect the fax each time we send and recieve.

I wish there is an easier way to explain this, but I hope you get the idea.

FusionNet

have you any filter on the line anywhere?

Solair

It's a weird quirk of British telephone wiring again I'm afraid.

Irish telephones carry the phone signals on the two centre contacts of the phone socket. UK phone sockets carry the signal on the outer two contacts.
Some manufactures of faxes and modems parallel the line on the UK and standard RJ11 (Irish positions). This saves them the hassle of having to make a special UK version. They just crimp a UK phone plug onto one end of an RJ11 cord and plug it in and it connects.

The problem is that Irish telephone sockets use the outer pins for an entirely different purpose and plugging one of these UK spec'd faxes directly into an irish line will cause all sorts of problems i.e. phones may not ring / you may get no dial tone it may short out the line! You would get an identical problem if you were to plug this fax into a US or Canadian phone outlet too. US phones often carry the second line on the outer pair! so you'd actually end up connecting your two lines together!!

It's likely that your computer's modem only has 2 contacts i.e. the centre two so would have not passed through the other 2 incorrectly connected terminals on the fax machine thus not short circuiting your phone line.

See if you can find a phone cable in your house that only has two wires connected. If you look at the plug carefully, you will see that only the centre two wires are connected (red and green usually). Most phone wires connect 4 terminals, even though the outer two are not normally used.

Sometimes microfilters for ADSL only carry the two centre wires too, so it might be worth looking at some of those if you only see two contacts on the filter, plug your fax in with it and it should solve the problem.

Failing that, get a cheap telephone socket in a hardware shop. Get a short telephone cord and connect ONLY the red and green wires to the red and green terminals on the phone socket.

Plug in your fax and plug the DIY telephone socket into your line. It should work fine!

Unfortunately there's no way to compel manufacturers to wire RJ11 sockets correctly. They're an official standard in the US/Canada and Ireland but they're not officially recognised in the UK even though they're used on all sorts of devices. Manufacturers completely disregard the wiring rules for them and create all sorts of problems for end users in Ireland and elsewhere. Even a UK user plugging into a PABX (office phone) socket might have issues!

This DSL filter would possibly solve your problem as it only passes through the centre two contacts i.e. the line:



See the way there are only 2 contacts inside the socket.
If you can find a filter that only has 2, give it a go!

reidyg

Thanks for the descriptive reply. Was working the weekend but I'll pick up a new 2-pin cable tomorrow. But I was just wondering, when I had dial up a few years a go, I had to get a 2-pin cable for my modem and the pins had to be reversed on one end. Is that the case for a fax as well? Or is that the purpose of a filter?

Solair

Again, that sounds like the modem's wired 'incorrectly' for the UK.

What happens is that the manufacturers are too cheap to provide a correctly wired cable. Both RJ11 and BT-style connectors are crimp-on and can just be easily attached to flat telephone cable.

To make it simple, they mis-wire the RJ11 connector on the device (modem/fax or whatever) in the BT configuration with the line carried on the wrong pins. They then just crimp the BT plug onto the cable and the RJ11 on the other end and it works, provided it's never used with a correctly wired RJ11 cable!

Your crossed over RJ11 to RJ11 cable is just a a way around the weird pinout configuration on the British specified device.

It's a total mess and there really should be enforced rules about wiring RJ11 connectors as it causes no end of confusion for customers.

The general rule of thumb is that if a device comes with a BT connector, use a BT adaptor and the original cable supplied rather than substituting it with a normal telephone cable. Sometimes they're correctly wired, but quite often they're weird pin layouts.