View Full Version : More than one ADSL modem on the same phone line?

John H
16-04-2004, 10:05 AM
Is it workable to have more than one adsl modem operating at the same time, through the same ISP, on the same phone line?



16-04-2004, 10:07 AM

John H
16-04-2004, 10:13 AM
Thanks gf - an economical response...

Oh well, another idea for a workaround to a problematic networking issue down the gurgler. Back to the drawing board...

16-04-2004, 10:50 AM
Whats the probematic network issue?

The reason for the constraint of 1 modem per line is that they would simply conflict with each other as they share the same frequency spectrum.
Neither could work, just the same as 56k dial-up modems cannot share the same line at the same time.

John H
16-04-2004, 11:31 AM
OK, thanks - that makes sense.

The problematic network issue is that my office is in an outside building, where I have a desktop PC and a laptop both connected to a Dynalink RTA300 adsl router. Also connected to the router is a WAP.

My wife's laptop in the house connects to the WLAN via a USB wireless adapter. Generally it works fine, but of late it keeps dropping the connection. Frustratingly this is often the case when the laptop is in the middle of a large download, or when she is part way through composing a complicated email or database entry when connected via the WLAN to her school's First Class server or database (using Citrix Client).

For other reasons, that laptop has recently been formatted and freshly reinstalled with WinXP Pro and all updates, so it should be in hunky dory condition. The network dropping pre-dated the formatting and reinstallation. I have tried two different USB wireless adapters of different brands, and the only difference is that network dropping happens more frequently with one than the other.

When you are working on the laptop, everything seems to be going fine, then up pops the dialogue box saying there are available wireless networks and would I like to view them. That is the signal that the network has been dropped, and in the process of reconnecting part complete work is lost.

I am stumped as to why this is happening, after about 18 months of successful operation. That is why I wondered whether to chuck the network idea altogether and get a separate adsl modem just for the house laptop. I do use the WLAN daily to synchronise files across all three computers, so there is a good back up strategy in place, but I don't have to do it that way and could easily drop the house laptop out of the network provided there was another way of connecting it to the net.


John H
16-04-2004, 11:36 AM
I should have said that all three boxes are on WinXP Pro, with the office laptop dual booting with Xandros 2. The WAP is a Linksys WAP11 with signal booster and an external aerial, and the two USB adaptors I have tried are the DSE adapter ($49) which works far better than the Linksys WUSB54G Wireless Ethernet Adapter ($150). I have also tried a Linksys PCMCIA Wireless Ethernet Adapter and it does the same thing.

This may be off the wall, but is wireless affected by the weather conditions????

Big John
16-04-2004, 12:06 PM
> This may be off the wall, but is wireless affected by
> the weather conditions????

They can be affected by the new cordless phones. The ones in the 2.4Ghz range.

16-04-2004, 12:09 PM
Your problem is not unique.

I have a cvolleague (in Wellington) that has exactly the same issues, which were improved by ditching the USB in preference for a PCMCIA adapter, but not cured.

I am sure its not weather. He is all indoors.

I use Belkin gear here and have no problems at all.

I would like to understand why, as well. He has eliminated cordless phones etc.

John H
16-04-2004, 12:25 PM
Thanks BJ and gf. I do have a relatively new 2.4Ghz phone in the outside office.

Can they interfere with the WLAN even if they are not in use at the time (i.e just sitting in their cradle) or do they need to be transmitting?

If they need to be transmitting, that would not explain the change, but if they interfere just sitting idle in the base station, that may be the issue... Darn, that phone cost a bomb.


16-04-2004, 02:52 PM
Unsure about the cordless phone needing to be "on"

The DECT type seem to have a polling function, as one here "knows" that the base station is on. That indicates the base station may have a constant transmit. Its 1.9 MHz though, so not a direct problem (but I don't have a problem with my WLAN anyway). Certainly the distance that my WLAN will work over is not flash (20 - 30 m max) but within that its reliable.

I do have another 2.4 Ghz cordless phone though and that cohabits with the WLAN OK.

Also a 2.4 GHz video link operating from time to time and while that link suffers because of the WLAN, its not seemingly affected the other way around.

Also your microwave oven is operating around 2.4 GHz ...

John H
16-04-2004, 04:13 PM
Well, I took the phone off its cradle and unplugged the cradle from power and phone line to see what happened. Still had dropping network syndrome. I then realised the batteries were still in the handset (duh!) so that probably wasn't a good test.

I then took the batteries out, and left the laptop on but still got dropped network.

I then gave up, and fired everything up again including the phone. The network has been stable since then for about an hour and a half (shhhh!).

I remember the guy who sold me the phone said that you should have the wireless network working when you first power on the phone. He said that the base station searches for existing transmitters and then sets itself to avoid conflicts. I guess it is possible that this didn't occur properly when I set the phone up the first time...

Wouldn't it be sweet if it has now unknotted its knickers through being completely powered down and resetting itself on power up whilst the network was functioning (I notice that the date on the phone has reverted to default).

Then again, I am not going to hold my breath until a pig flies overhead...

16-04-2004, 04:16 PM
The guy was correct, they search for a clear channel so having the WAP running first is a good idea.

Ooh look - a pig just flew past the window ... good luck.

John H
16-04-2004, 06:26 PM
Well chaps, a pig just flew over Papanui as well. I think it must have been the 2.4Ghz phone not being set up properly.

The network has been up without pause all afternoon, since I powered down the phone and powered it up again some time later. Too much to be a coincidence I think?

Thinks... Nervously tries to contact the house laptop and it is still up. When can I uncross my fingers....

Thanks for your assistance.


John H
18-04-2004, 09:43 PM
Oh dear. It was a false alarm. The same problem has re-occurred, and nothing I have done can fix it. Getting rid of power etc to the 2.4Ghz phone does not solve the problem at all. I wonder if the neighbours are using such a phone? Or whether my WAP is dying?

Maybe I should dig a trench and a bore hole in the wall of the house and the office and lay a cable. It may be cheaper in the long run. The only problem is I would have to move a great deal of my stack of winter firewood to get the best lay for the cable.


Graham L
19-04-2004, 04:39 PM
I don't trust porcine aviators either. So they behaved like pigeons after all.:D

John H
19-04-2004, 05:19 PM
True. I called the local wireless expert in ChCh, and he says that wireless networks are being stuffed all over the place because of the proliferation of 2.4Ghz phones, and other new wireless networks.

He is constantly having to attend and problems solve these breakdowns of networks that were formerly quite successful.

His informed guess is that one of my neighbours has purchased one of these damned phones or there is a competing network in the vicinity.

He recommended I change my WAP channels. I told him I had already changed from 6 to 8 but he said that they can overlap as many as four channels so I should go up or down to the extremes. I have channels 1 to 11 available and have tried both 1 and 11, as well as 6 and 8, but still no joy.

I think I am reduced to laying a cable, which is what I should have done when I laid the telephone cable when I had the outside office built, but I already had a functioning WLAN at that stage and didn't see the point. It wasn't broke so I didn't fix it. Hindsight is 20:20, eh?

The problem is that the logical route for a cable is behind about 6 metres of firewood... Having stacked it once already I don't want to break the stack down and rebuild it!


Graham L
19-04-2004, 05:29 PM
You could try making your links more directional. If your base unit has exposed antennae, a simple reflector (made from cardboard and aluminium foil) could give you much better signal strength. Try a few searches on Google, which should find a number of sites with plans. "wifi antenna", "wifi reflector", "wifi homebuilt", etc, might work.

John H
19-04-2004, 06:26 PM
That is the next thing that the wireless guy suggested, though he thought it may be overkill in the circs. His site is:


I may give it a go anyway, because it is going to be a long time before I use up sufficient firewood to lay the cable, and I already have an antenna outside on the office verandah post so the wiring is already there.

Thanks again.

19-04-2004, 06:34 PM
Unless the wiring you already have uses VERY expensive coax cabling (and not ordinary TV coax) it simply will not work. I note that is also stated on the site linked in your post.

Of course you could always just drape the cable behing/under/over the firewood and bury it when winter is over. And the ground in Papanui will have thawed by then.

Putting it in some garden hose would be adequate protection for naw.

John H
19-04-2004, 06:54 PM
>Unless the wiring you already have uses VERY expensive coax cabling (and not ordinary TV coax) it simply will not work.

Do you mean the wire to the antenna gf? If so, it was the wireless guy that made up that extension lead for me, because I need the adapter at each end to connect the WAP to the antenna and he made up the cable. It does work, very well, so he must have used the cable he recommended on his web site ;-)

>Of course you could always just drape the cable behing/under/over the firewood and bury it when winter is over. And the ground in Papanui will have thawed by then.

Wow, that is pretty cheeky. Seeing you live in Big Island I will forgive you though - clearly you live on the Mainland with me so you understand these things. and yes, draping over the firewood may be a good idea.

>Putting it in some garden hose would be adequate protection for naw.

Naw as opposed to thaw... Not a bad idea gf - I was going to get some electrical conduit pipe which is what I put the underground telephone cable in, but hose would be cheaper and more flexible for firewood draping. Ta

In the time it has taken to type this, the network has gone down three times. Grrrr.