Q: I recently purchased a Wi-Fi-enabled HDTV, along with a new cable modem Internet connection. My router is a Netgear WNR2000x3, which the cable-modem tech said was at least as good as anything he had to offer.

The cable modem connects via Ethernet to the router, which in turn connects via Ethernet to my two PCs (which work fine). The HDTV is in the next room and my cable modem is not near any telephone lines and only has one wall between the modem and the HDTV. I got the modem off the floor and noticed some improvement. The protocols for both router and TV are both 802.11n.

My question is about the drop-off of download speeds I’m experiencing between the Ethernet connection(s) and the Wi-Fi. Typically, the cable modem runs at about 28 to 29 megabits per second, while the Wi-Fi connection (as tested on the HDTV) comes in at speeds varying from 8 Mbps to as high at 18 Mbps, depending on the time of day and other factors. It averages out at about 50 to 60 percent of the Ethernet connection speed for my PCs.

Is this usual for Wi-Fi connections vs. Ethernet, or should I be looking at another router or other symptoms? There seems to be very little information or explanation about this difference that I can find on the Internet, and I’m sure many others experience this dilemma.

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— Lorin Grinolds

A: Network connectivity issues are the trickiest to diagnose and really require hands-on troubleshooting. But I’ll give you some general principles.

First, yes, Wi-Fi is still significantly slower than Ethernet. While Ethernet connections can move as much as 1,000 Mbps of data per second, 802.11n maxes out at about 300 Mbps. (The new 802.11ac standard raises the Wi-Fi throughput to about 430 Mbps.)

So, no matter how you cut it, a wired Ethernet connection is still going to be at least twice as fast as a Wi-Fi connection.

And your internal network — both Wi-Fi and Ethernet — is going to be faster than your cable Internet speed as long as there are no bottlenecks.

But what about bottlenecks?

Troubleshooting performance problems on networks is difficult because networks — even small ones — tend to involve quite a number of different pieces of equipment. Cable modems, routers, client Wi-Fi adapters, client Ethernet adapters. Any one of these can be a bottleneck.

The first step to improve performance is to make certain the drivers for all the devices are current.

Next, be aware that cable Internet bandwidth goes up and down depending on how many subscribers are using it at the moment. Sometimes the differences in bandwidth can be significant. So notice if you see a pattern in the timing of low Internet speeds.

The most reliable part of your network is wired Ethernet connections. Wi-Fi connections are notoriously vulnerable to a variety of potential sources of interference. Yes, distances, walls, floors and ceilings all cut into Wi-Fi transmissions, especially if the structure has metal in it. Microwave ovens, or other high emitters, can also cause problems.

Wi-Fi can also be a problem if you’re using channels that are crowded with other users. You can download programs that will show you activity on Wi-Fi channels so that you can select the least crowded one. One such scanner is available at www.inssider.com.

Wi-Fi routers also vary significantly in their power, depending upon the number and type of antennas they employ, as well as software and other circuitry. In most cases, you get what you pay for. Even if you’re selecting among 802.11n routers, there’s a big difference in performance and generally the lowest-cost devices don’t deliver the best performance.

Also, 802.11ac are now available that will deliver better performance. Bear in mind, however, that while the routers are backward compatible — and can accommodate older clients — you’ll only get better performance when you also have an 802.11ac client adapter.

Questions for Patrick Marshall may be sent by email to pmarshall@seattletimes.com or pgmarshall@pgmarshall.net, or by mail at Q&A/Technology, The Seattle Times, P.O. Box 70, Seattle, WA 98111. More columns at www.seattletimes.com/columnists.