Adjust DD-WRT TX power

I had a DD-WRT router that was dropping a lot of packets. I got a lot of errors and that caused poor playback in Netflix and especially MLB.tv. It wasn’t a bandwidth issue. My wireless network connection was just too noisy. I had to adjust my DD-WRT TX power to fix it.

I probably adjusted it the opposite way you would expect.

Checking the error rate
dd-wrt tx power

As you can see to the right, I was getting errors 6.8% of the time. A few errors are OK; but 6.8 percent of the time is too much for some applications to handle. To check your error rate, navigate to Status, then Sys-Info in the DD-WRT user interface.

Adjust DD-WRT TX power

The key was to tweak the router’s TX power. In your DD-WRT user interface, navigate to Wireless -> Advanced Settings, and you’ll find a setting called TX Power. On my Linksys devices, it’s measured in mW. On my TP-Link box, it’s measured in dBm. One dBm is 1.2568 mW.

For me, reducing the power to 40 mW dropped the error rate down to a more acceptable 0.6 percent.  Linksys routers usually default to 71. My TP-Link is set to 20 dBm but it self adjusts to 16 dBm, which translates to 39.8 mW. That convinced me that 71 mW might be more than I needed.

Indeed, when I lowered the power on my problematic Linksys to 40mW, the error rate dropped from 6.8 percent of the packets to a tolerable 0.6 percent. Dropping it down to 38 mW dropped it closer to zero. You won’t completely eliminate the errors, but you can get it below 0.1 percent. A few hundred errors over the course of a week isn’t worth worrying about. A few hundred thousand will cause you problems though.

Our tendency when we load DD-WRT is to crank up the power to over 200 mW, which can be counterproductive. Sometimes less power is actually better, because more power also means more noise.

Checking the results

Navigate back to Status, then Sys-Info and look at the SNR on your wireless connections. Once it’s below 50, you know you have a good setting for your transmission power.

There was another side effect as well. I have three routers, with two configured as access points. My noisiest router also happened to be my slowest one, so ideally, I would want more of my traffic to go to the faster ones. It wasn’t working out that way. Reducing the transmission power helped considerably. My wireless devices started to favor the ones in closest proximity, rather than clinging to the slow and noisy one.

So if you have more than one access point, try tweaking the TX power. If you get errors, drop the power until the errors go away. And on your fastest routers, increase the power a bit until you start to see errors, then back off the power until they go away. You’ll improve your range and performance.

2 thoughts on “Adjust DD-WRT TX power”

  1. This is all rf right? When I was dealing with radio teletype we would get many errors from a clear and loud signal if the receiving bandwidth was too narrow, widening the bandwidth would solve the problem as the whole signal could be captured. What you’re suggesting is sort of the opposite, diminishing the signal strength to the point it can all or nearly all be captured within the apparently fixed band width. Good call.

    1. Interesting. On some 802.11 devices you can do an extra-wide channel, which would increase the bandwidth, but I don’t know that all hardware supports these wider channels.

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