Best way to determine source of home network slow downs?

"From my own personal experience I can tell you the two most likely culprits.

Since you are using a wireless router you have the likely issue of interference. FCC rules basically state that your device must accept interference even if it causes undesired behavior. Being that these devices use an unlicensed band, you can never be sure when someone starts transmitting on the same channel you are using. So to that end a wireless ""site survey"" is in order. There are some very sophisticated tools for this purpose but those tools get a bit pricey. So this is the poor man's site survey method....

Within your wireless network utility pull up the connection manager and get it to show you the networks within range. Each utility is a bit different but they all generally have the same functionality. Be sure to take notice of the signal level and the channels that are in use. Any channel you see in use is most likely a channel you want to avoid. So lets say if you are on set to use channel 6 and you see another SSID also using channel 6, you would want to change your channel to one that is not in use. Depending on the population density around you, you may have lots of interference or not much at all.

Keep in mind that the best channels to use are 1, 3, 6, 9 and 11. These channels do not overlap with one another and you stand the best chance of getting good results.

Cutting the interference usually solves the problem you have.

Another thing to consider is that your upstream provider may be having issues. Cable modems use a shared medium, so high usage in your neighborhood might just appear as such a problem as your connection slows down as a result.

Comcast is particularly noteworthy as their network seems to mulfunction all throughout the day. I determined that Comcast's DNS servers were not responding and my pages would time out trying to load. I set my connection to use external DNS servers located on the internet to bypass the flakey DNS from comcast.

This is a good bit of info, but should give you something to get started with."

I agree with JFV. Wireshark is one of the best tool for the job for network slowdowns. It may be a good tool to check if anything in your network is using the bandwidth unexpectedly without you noticing. I am also having the same issue, but I'm thinking about calling the ISP for a better understanding of whats going on.