External monitor causing slow wireless

Hello Everyone,

First let me say that I've contacted Apple Technical support about this issue on two separate occasions, spending several hours on the phone with them in the process.

I've also noticed several other users posting problems similar to the ones that I am having.

The problem I am having occurs whenever I connect an external display to my Macbook. As soon as the external display is connected (via the mini-DVI to DVI adaptor) my wireless connection's speed drops dramatically. Normally it is around 14 Mbits/s and it drops to ~ 1 Mbit/s.

If i disconnect the external display the speed jumps right back up again (even with the Macbook right next to it). The strange thing is that the wireless connection strength is at full regardless of whether or not I have plugged in the external display.

I have also measured the interference of my airport connection using a utility called AirStatz. The interference is the same regardless of whether or not the external display is plugged in (low interference).

Here are some other things I have tried.

Changing the channel, tried 1,2,6,10,11 - no real difference.

Changing from 802.11g to 802.11b did help somewhat, but the speed drop still occurs.

For example with 802.11g the speed drops from ~ 14 Mbits/sec to 1 Mbit/s and using 802.11b the speed drops from ~ 4.5 Mbits/sec to 2.5 Mbits/sec. 802.11b has a maximum throughput of around 5 Mbits/sec.

This issue was present on 10.4.9 and also now in 10.4.10.

This issue started around the time I installed the battery firmware update for the Macbook.

My theory is that the external display draws more power from the Macbook and therefore the wireless card doesn't have access to the necessary power it requires. To further test out this theory I conducted various tests with the Macbook LCD display at different brightness levels (not the external display). Lowering the brightness on the Macbook's LCD display did seem to help in my speed tests but not significantly.

This issue is really bothering me, I do lots of programming for work and having a larger display really helps.

If any other Macbook owners could run some tests for me, by connecting an external display and performing a bandwidth test I would greatly appreciate it. Also if there's anything you think I should try let me know.

One can use www.speedtest.net or www.speakeasy.net/speedtest to get some results.

I know that I'm not the only one with this issue, but I'm sure many people that connect their apple portables to external displays are probably using Macbook Pros so the issue might be somewhat rare.

Thanks for reading this post,

Robert