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First GAN, then HAN (home-area network)

Aug 02, 20044 mins

A few weeks ago we discussed what one reader referred to as our garden-area network, or GAN, and we got a few interesting pieces of feedback.

One reader pointed out a small glitch: If you visited the Web page where we posted some photos of the installation you could click on the pictures to display enlarged versions in pop-ups. But if you were using Netscape 7.1, the pop-up windows didn’t work.

This was a “d’oh” on our part, as we had defined a JavaScript pop-up function in the HEAD section like this:

function cPop(url, wide, high)


+ wide + ',height=' + high)}


This function was called from the page BODY by the following code:


Or rather, in the case of the lucky Netscape users, wasn't.

The reason was the scripting language needed to be identified as "javascript" rather than "jscript," the latter being a Microsoft-only keyword. OK, now onward.

Reader Vinny Fasano wrote about our problem with X-10 signal loss over power lines: "The obvious answer is which phase of the AC line the controller and modules are located on - in addition to signal amplifiers, there are phase couplers that will bridge the signal from one leg to the other effectively. A small capacitor does the job pretty well."

We tried a plug-in phase coupler  in a two-phase socket in the barn, but it might have been because the socket was at the end of two circuit legs both some 200 feet from the main panel that no effect was seen. We suspect we'll have to invest in a serious phase coupler if we want to get the job done.

Fasano also pointed out that UPS and computer power supplies contain surge and noise suppression, designed specifically to filter power-line abnormalities. Unfortunately, X10 signals look a lot like noise to these devices. To get around this problem you can use "filter fliters" on the equipment to reduce the attenuation.

Long-time reader Phil Daley couldn't help himself: "I have no problem with walking out to the yard twice a day, once to turn on the water and, an hour later, to turn it off. Good exercise."

Really? We find that running around tracking faulty valves, broken sprinkler heads and wiring problems gives us more than enough exercise.

Now if the GAN and the network in our office were all the networking in our house it would be fine. However, that is not the case, which leads us to our next topic.

First, our house has plaster walls that we think are supported by metal lathe. The result of this robust construction is that radio signals in the 2.4-GHz and 5-GHz ranges used by 802.11x network gear are severely attenuated.

When we rewired the house we put in a few Category 5 cables but not enough. So when network access was required in a room on the other side of the house, the choices were clear: We would have to navigate the ceiling void dragging cables around; crawl through the crawl space under the house also dragging cables; or see if power-line networking was a go. Guess which plan we chose?

We invited several vendors to play. First in was Netgear, followed closely by Linksys.

Both companies' products are easy to set up although the instructions for both would, we suspect, not be completely clear to consumers and might even annoy seasoned IT professionals such as yourselves.

The products - the Netgear Wall-Plugged Ethernet Bridge XE102, the Linksys Powerline EtherFast 10/100 Bridge and LinkSys Powerline USB Adapter  - are based on HomePlug.

HomePlug transmits data over power lines at frequencies between 4 MHz and 20 MHz using Orthogonal Frequency Division Multiplexing (OFDM). OFDM splits the data into parts that are transmitted simultaneously at different frequencies and reassembles them at the receiver.

HomePlug devices monitor the signal-to-noise ratio of each frequency channel and "back off" from using the noisy channels as required to ensure a reliable data transfer. This results in a lowered data rate when there is power-line interference from appliances such as microwave ovens.

Clever stuff, and you'll find out just how clever next week. Send your signals to


Mark Gibbs is an author, journalist, and man of mystery. His writing for Network World is widely considered to be vastly underpaid. For more than 30 years, Gibbs has consulted, lectured, and authored numerous articles and books about networking, information technology, and the social and political issues surrounding them. His complete bio can be found at

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