Ask the Wi-Fi Guru, Episode II

Ask the Wi-Fi Guru, Episode II

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Written By Aaron Weiss

In Episode II of this new monthly column, Aaron Weiss, our resident Wi-Fi Guru, will answer your burning questions about small-scale Wi-Fi deployments. In this special, themed episode, he covers a variety of ways to extend your range.

The Wi-Fi Guru is once again on hand to help sort out your wireless networking questions, quandaries, and calamities. You might recall that in the debut episode of Ask the Wi-Fi Guru, we selected several of your questions, and…well…answered them. Because that’s how it works. We’ve received lots of great and interesting questions since then. The answer to some of these is simply “I have no idea.” So, if yours doesn’t appear this time, that might be why. Unfortunately, we can only respond to a few questions per installment. The Guru also encourages you to visit the Wi-Fi Planet Forums to seek the wisdom of the crowd.Since we’ve received many questions about signal range, consider this a very special, themed episode of Ask the Wi-Fi Guru.

Q: I wish to extend the range and performance of my laptop wireless card when used from my sailboat. I have a Wi-Fi antenna installed on the masthead with a coax terminated with a mini UHF connector. It seems that repeating a WLAN signal is what I need to do, as I’m trying to improve performance to Wireless Access Points available at many ports and anchorages. Can you recommend a good technology to use between my external antenna and my laptop PC to accomplish this? — Cpt Monty

A: Wireless networking on the high seas gives a whole new meaning to computer pirates. The good news is that if your sailboat were commandeered by rogues, and if one of those rogues was the helpful kind who isn’t looking for trouble, but instead looking for trouble to solve, he would answer your question with an enthusiastic Yar! A wireless repeater is exactly what you can use in this situation, and you can do so quite cheaply using the free firmware DD-WRT loaded onto a compatible router such as the Linksys WRT54G series. We’ve even published a tutorial on configuring this exact combination as a repeater.

You will probably need an adapter to mate your mini-UHF connector with the antenna jack of a router. The WRT54G routers use an RP-TNC connector, but DD-WRT supports a wide range of routers, some of which may use other types of jacks. I haven’t found a direct mini-UHF-to-RP-TNC adapter, so you might need to string together a couple of adapters, or buy a short length of custom cable with the appropriate connectors at each end. Do be sure that a router you choose has detachable antennas.

Once setup, you can access the router’s administration interface from your laptop. In DD-WRT you can configure advanced wireless settings to direct the router to use your external antenna for sending (TX) and receiving (RX). Using the router’s interface you launch a scan for available networking using the fabulous visualization tool called WiViz, built in to DD-WRT, which will display a real-time radar view of access points within range of your boat.

When you configure DD-WRT as a repeater, you will define a virtual wireless network (SSID) that will be re-broadcast on your boat, which you can connect to wirelessly from your laptop. Ahoy!

(Big aside: If for some reason you cannot get DD-WRT repeater mode to work to your liking, the second and slightly more complicated solution is to build your own repeater using two routers, with one running DD-WRT in client bridge mode. As in the first scenario, you will connect your mast antenna to the DD-WRT router and use it to scan for and associate with an available network. But instead of trying to configure DD-WRT to also repeat the signal, you would use an Ethernet cable to connect a LAN port on the DD-WRT router to the WAN port on a second wireless router of any make. This second wireless router would then “see” your DD-WRT router as a broadband connection, and broadcast it on your boat just like any DSL or cable connection.)

Q: I am desperately trying to find a wireless router to buy.  I have had a Belkin pre N and a Belkin N1 Vision.  I found the pre-N a better performance machine.  However now I want to buy a new router that has great coverage from a main house to an annex house.  There are walls to consider. I need coverage up to about 150 ft.  What is your personal choice?  – Nick

A: One thing to note when setting up a wireless network is that range and speed are two different things and you may need to optimize for one or the other. In the Guru’s experience, pre-N gear can do a good job with range, but is aggressive about reducing speeds to compensate—so you may get a connection from a distance you couldn’t with another router, but it might not be very fast. The reason pre-N gear is generally good at range, and obstacles, is because it uses MIMO—or multiple antennas—to “capture” reflected signal paths. You can also find MIMO on some enhanced ‘g’ routers, which usually say so right in their name, like “Super G with MIMO”.

To get the most out of any router with MIMO, you need to use a wireless client with the same support. (It’s not clear from your question if you are also using the Belkin pre-N card at the other end.) The Guru does not like to encourage vendor lock, but in practice, edge technologies like MIMO (and “RangeMax”) as well as pre-N seem to be most reliable when paired with companions of the same vendor.

Besides all that, if your router has detachable antennas (the typical “rubber ducky“), you can swap them for longer, more powerful replacement antennas that can double or sometimes triple their sensitivity. This doesn’t necessarily mean a doubling or tripling of your range, but it can help you squeeze out every last drop of performance.

Try to orient your wireless router as high as possible in your main house, such as a top floor. Alternative possibilities could include adding a second wireless router to your main house, in a spot best for “seeing” the annex house (such as a window). This secondary router could use WDS (wireless distribution system) or an old-fashioned Ethernet cable to connect with the primary router for service.

A third possibility would be to setup a wireless router in the annex house and use WDS to repeat the signal from the main house. You would be able to setup this annex router in an optimal position (and/or with a stronger antenna) to receive the signal, and your wireless clients could more easily pick up the rebroadcast signal.

For a 150’ range, one or any of these scenarios should do the trick. For longer distances, I would start to look at directional antennas like yagis to create a point-to-point link. But this seems like overkill at this distance unless your houses are actually underground fallout shelters. Which would be pretty cool, actually.

Q: I have a big problem. I need to share an Internet connection with my father, but we live 600′ away from one another, and we have a few trees in our sight line. I tried a few new routers, but they only go like 200′. Do you have any suggestions? Will any repeaters help…could I use two repeaters or three? – Unsigned

A: Six hundred feet is indeed a far distance in wireless networking speak, although if this were a personal relationship column, 600 feet from a parent might not be nearly far enough. Using repeaters in this scenario might not be the best solution. For one, each repeater will reduce your network bandwidth. Two, assuming these houses are outdoors and not inside a glass bubble like in the underwhelming Simpsons Movie, the span between them is outside, and installing networking gear outside adds an extra level of complexity (power, weatherproofing, and thieves, for example).

Unlike the writer with a 150-foot span, you will want to use directional antennas connected to wireless routers in each house. It sounds like you have a reasonable line of sight between houses—a few scattered trees should not be a big problem; a forest, or a steel wall, might be more significant.

It sounds like the Internet connection is at your father’s house (hopefully he pays for it, too). You want one wireless router there, with an external directional antenna. This means you need to choose a router with a detachable antenna so you can connect a replacement. In your house, you want to use a wireless router that can be configured as a wireless client. The easiest (and cheapest) solution is to use DD-WRT with a supported router like the Linksys WRT54G, just like the sailboat captain in our first question. Buy yourself two yagi antennas, with appropriate connections or adapters to plug into the two routers. Connect each antenna to a respective router in each house and aim them at each other. Chances are, this will do the trick. You may even be able to keep the yagis indoors, especially if you can position them by windows. Installing the yagis outdoors is a little more complicated because you’ll need to run the cable indoors to the router.

If for some reason yagi antennas aren’t strong enough, or you need to connect a wireless link much longer than 600 feet—say, several miles—you can upgrade to a directional grid antenna. Reminiscent of a medium-sized satellite dish, a pair of grid antennas will cover a significant distance. But, as always with wireless, the more clear your line of sight, the longer a link you can achieve.

Aaron Weiss
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