In the early spring, some lawns green up faster than others -- and it looks like that's also the case with Minneapolis' newly seeded wireless Internet system.

The long-awaited Wi-Fi network is completed and working. Parked at 60th Street and Washburn Avenue S., I could surf the Internet on my laptop with download and upload speeds of nearly 1 million bits per second -- or nearly every drop of the Wi-Fi speed I pay for every month.

But if you roam with your laptop, depending only on the internal Wi-Fi gear that came with it, what can you expect? With my laptop beside me, I drove around the city to find out -- and learned that the laptop Internet experience may vary a lot.

When I parked near the swimming beach at the south end of Lake Harriet, I got less than half Internet speed I'd found before. Sitting on the beach itself, I got no Wi-Fi service at all.

What gives?

It seems that the Wi-Fi in the air isn't equally strong everywhere. At 60th and Washburn, I was half a block from an antenna. At Lake Harriet, the antennas were farther away, on Lake Harriet Parkway, which is set back from the lake.

For most home Wi-Fi customers, differences in Wi-Fi signal strength are evened out by special Wi-Fi booster modems available through network builder US Internet of Minnetonka. With those modems ($5 a month to rent or $80 to buy for your house; $160 to buy for your laptop but no rental), your chance of getting a 1 million-bit-per-second download is 99 percent or better, the company says. US Internet notes that its contract with the city guarantees only modem-assisted reception.

As a result, laptop users roaming city streets without special modems can expect more uneven Wi-Fi coverage. If you're close to a city light pole with a Wi-Fi antenna, your laptop reception probably will be quite good. If you're farther away -- say half a block -- reception may be slow or nonexistent. For example, roaming with a laptop will show you: