I've noticed some network operations on the LAN going slower than usual over the past few weeks but hadn't had the chance to really pay much attention to it.

Today I was making some edits to music on a Windows from my Mac and it was painfully obvious things weren't going as fast as they used to.

So I did a quick test... Transferring a 150MB folder of MP3 files averaging 6MB or so in size I was getting about 1-1.5MB/s average on 802.11n. On 802.11g I get over 2MB.

I tested both to the Windows share as well as to my Time Machine share with the same results. The Windows machine says it's only using less than 1% CPU and less than half a percent of network bandwidth when all this is going on.

I'm pretty sure I used to get about 7MB+/s using 802.11n

Anyone else see any similar strange behavior after updating to Mac OS 10.5.7? It's the most major change I can think of that I've done to the system in the past month.

Are you running your N network in the 2.4 ghz space or 5.8? Do you use wide channels? And lastly, check Network Utility in OS X and see what connect speed it shows for the wireless.

I have one of the new dual-band Time Machines BTW.

I'm running 802.11n on the 5GHz band with wide channels. In fact I keep the TIme Machine set to restrict n to the 5GHz band.

Network Utility reports 270 Mbit/s link speed. And during the copy it reports no collisions nor errors.

If I set the radio on AUTO, which allows n on both frequencies, I can get an average of 4.8MB/s running n on the 2.4Ghz radio.

If I set specific channels instead of leaving that on AUTO like it's always been, it seems I can get the 5GHz radio up to about 4MB/s using channel 36 - I'm testing the others now.

When I set this up a few months ago, the benefits at 5GHz were obvious over 2.4, with consistently higher throughput.

Ok, this seems to be a case of interference.

I have ruled out my 5.8GHz cordless phone system when not in use (unplugged all batteries and disconnected power from base stations).

I have also disabled my network filter while testing.

Interference robustness turned on can get my up to 4.7MB/s. This setting normally helps in noisy environments and says it can slow performance. In my case, since the interference is killing performance, this actually improves it.

I'm still 2MB+/s shy of where I'd like to be though.

Here's a strange one... Even if I connect only to the 5GHz radio, I am getting consistently better through-put if I keep the radio setting on the base station on AUTO which allows n connections at 2.4GHz.

How do I find out where this interference is coming from? And should I start to make plans to set up a faraday cage around my house?

Running iStumbler (98) I can see that even in the same room as my base station, signal strength for my networks is pretty low. 65% for 2.4GHz and 59% for 5GHz. I'm about 10 feet away from the base station (MBP about 2 feet lower than base)

And back in the same room I was initially testing in, which puts the computer maybe 15 feet away from the base station, but with two sections of wall between, signal strength is at 58% and 43%. The 5GHz strength is actually lower than the signal strength of some neighbor's 2.4GHz signal. I have a few other neighborhood networks ranging from 40% to 47% at 2.4GHz from this location.

Something random to try, turn off wide channels and see if that changes it any.

Also, go to the Advanced, Logs and Statistics section on the Time Capsule, and see what it reports for signal and noise levels for your wireless client.

Turning off wide channels didn't seem to do anything. I tried it when I saw you first post about it...

I can't keep that 4.7MB/s I mentioned earlier consistently from this room. From the same room as the base I can actually get a solid 6MB/s.

Here are the stats (Rate sometimes jumps to 80. Mostly stays where it is though).

5GHz: Signal -74, Noise -90, Rate 54, Type 802.11a/n

With Interference Robustness and Wide Channels turned OFF:

5GHz: Signal -71, Noise -93, Rate 52, Type 802.11a/n

From the same room as base:

5GHz: Signal -57, Noise -91, Rate 135-162 (sometimes jumps to over 200), Type 802.11a/n (without Int.Robust)

5GHz: Signal -50, Noise -93, Rate 130, Type 802.11a/n (with Int.Robust)

For comparison, my Squeezebox which sits about 8" away from the base station:
2.4GHz: Signal -26, Noise -96, Rate 54, Type 802.11b/g

Somebody very closeby has bought a wireless video sender I guess. That is usually why you suddenly get a massive reduction in signal quality and corresponding throughput.

The rate and signal definitely seems much lower then it should be for some reason. From the opposite end of my apartment, I see -84, -83 on noise and a rate of 14.

A few feet away changes that to -34, noise of -91, and a rate of 243.

Both of these readings on the 5Ghz network, and using an older MacBook Pro.

Any suggestions on how I can confirm this? And maybe find out who it is? If it's not huge money I'd buy them a replacement system to get my network back in order.

Create a 1/2 cylinder reflector from some tinfoil and cardboard, and put it around the wifi antenna (or the entire base station if necessary). Then rotate and observe, to figure out which direction. Slow, and tedious, especially when the problem is so intermittent.

Cheers