Q: My speed has decreased from the router and the modem is working correctly, what can I do to increase the download speed with my Time Capsule 802.11n

A variety of phenomena can affect one's wireless network performance. You may be able to mitigate certain detrimental effects.

For solutions to potential factors that may be affecting your wireless network, please read Use Wireless Diagnostics to help you resolve Wi-Fi issues on your Mac - Apple Support.

What is the make & model of the Internet modem that you have the Time Capsule (TC) connected directly to by Ethernet? Which exact model is your TC? Has this always been the case, or just started happening recently?

Ok, a couple of things to point out:

1. Your 4th generation TC came out in 2009 and was discontinued in 2011. Typical consumer-grade networking hardware have a lifespan of 3-5 years. Yours is now past that timeframe ... and potentially, may be starting to fail.
2. If your Arris modem happens to be a Motorola SB61xx-series modem, these are known to be somewhat problematic with the Apple base stations. Neither are necessarily bad by themselves, they just don't "play nice" together.

No, that should be fine.

Let's assume, at this point, that the TC is NOT failing and try to troubleshoot why you are getting poor Internet performance with it.

I would like us to start by performing a complete power recycle of your networking hardware. Check out this AirPort User tip for details. Note; however, you will NOT need to perform the "factory default" reset at this stage, just the power recycling parts.

When completed, try testing your Internet speed again to see if this helped any.

If I was to purchase a new Apple router, would this solve my issue

Potentially yes, but no one here has a crystal ball that is good enough to predict what your performance might be in your home.

Since the only way that you will know whether a new AirPort will help in your home, is to try it out in your home, buy from Apple and you have a 14 day return privilege.

If the new AirPort does the job, then you are all set. If the new AirPort does not, then you can return it for exchange or refund.

But, before you do that, if you have not already done so.....connect your Mac directly to the modem using an Ethernet cable and run a few speed checks that way......to make sure that the modem is still performing correctly and that you are receiving the speed that your Internet plan specifies.

If it is, great. If it's not, then you will likely need to replace the modem......especially if you have been using it for 3-4 years or more.

Finally, did you run Wireless Diagnostics, as was suggested in the post from John Galt above?  If yes, what were the results?

You need to do a series of tests.

1. Plug a computer directly into the modem.. (you will need to power cycle the modem to pass the public IP to the computer) and do a few download tests.

2. Plug the TC back into the modem.. (another power cycle of the modem). Do the test again from the same computer using ethernet to each of TC lan ports.. wireless off in the computer and the rest of the network shut down. You need to do this as quickly as you can so you are testing the hardware and not the current saturation of cable in your area. There will be some level of difference.. I would say 10% within testing. More than that points to an issue. If it has slowed dramatically on ethernet the TC should be replaced (at least as main router).

3. I doubt after this long the TM902A will be showing issues only with the TC.. it would also show issues to the computer so I don't think Tesserax #2 comment is something to over worry about.

4. If you get good speed over ethernet, now test the wireless. Wireless speeds can definitely get worse over time. The exact why is probably as simple as component failure. The Gen4 TC in particular do have board issues which can suddenly go bad.

A factory reset of the TC is always worth a go. I recommend the following.

Factory reset universal

Power off the TC.. ie pull the power cord or power off at the wall.. wait 10sec.. hold in the reset button.. be gentle.. power on again still holding in reset.. and keep holding it in for another 10sec. You may need some help as it is hard to both hold in reset and apply power. It will show success by rapidly blinking the front led. Release the reset.. and wait a couple of min for the TC to reset and come back with factory settings. If the front LED doesn’t blink rapidly you missed it and simply try again. The reset is fairly fragile in these.. press it so you feel it just click and no more.. I have seen people bend the lever or even break it. I use a toothpick as tool.

N.B. None of your files on the hard disk of the TC are deleted.. this simply clears out the router settings of the TC.

 

Setup the TC again.

 

Then redo the setup from the computer you want to use for TM using Airport Utility.

1. Use very short names.. NOT APPLE RECOMMENDED names. No spaces and pure alphanumerics.

eg TCgen5 for basestation and TCwifi wireless name.

 

If the wireless is still a problem set wireless names like TC24ghz and set the 5ghz to different name.. eg.TC5ghz

 

2. Use all passwords that also comply with 1. but can be a bit longer. ie 8-20 characters mixed case and numbers.. no non-alphanumerics.

 

**3. If the TC is main router you can skip this point. (It is in your case but is here for completeness) This is only an issue when the TC is bridged.

Ensure the TC always takes the same IP address.. you will need to do this on the main router using dhcp reservation.. or a bit more complex setup using static IP in the TC.

Ignore this point if you don't understand it .. post back if you have drop out issues.

 

4. Make sure IPv6 is set correctly in the computer. ie link-local only for ethernet and/or wireless depending on which you use. Auto is not good enough.

No luck then the TC is just showing itself to need replacement. The current TC is getting well past its due replacement date so if the TC is at least working ok for ethernet I would think about a different wireless router.