Introduction
| Aerialix Mini Dipole Antenna | |
|---|---|
| Summary | Miniature antenna for wireless notebook adapters with external antenna connectors |
| Update | 10/8/2003 – Corrected available connector type info. |
| Pros | • Gets your laptop into same polarization as your AP • Can make a difference in weak signal areas |
| Cons | • Somewhat pricey |
Aerialix is a small WLAN equipment supplier located up in the Boston MA area. Among their small line of APs, antennas, cables and cards is a handy little item called the ARLX-OM-MINI2400.
The Mini is a hand-crafted omnidirectional simple 1/2 wave collinear dipole with a gain of approximately 2.15dBi. It’s specifically designed for the few WLAN PC cards that support external antennas via either MC or MMCX miniature connectors (see Table 1).
| MC | MMCX |
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Table 1: PC Cards with antenna connectors
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NOTE! Although MC and MMCX connector options are standard, Aerialix can make the Mini with any Cable “Group B” connector, i.e. Types MC, MMCX, SMA, TNC and N on a special order basis.
Although the Mini doesn’t provide much more gain than the integrated printed-circuit antenna built into your laptop’s wireless card, it has two advantages over it:
1) It’s much less directional – Anyone who’s used a wireless laptop that doesn’t have a built-in radio knows the contortions they often have to resort to in order to get a decent connection. The reason for this is shown in Figure 1.
Figure 1: PC card antenna gain plot
(click on image for a larger view)
From Antennas Enhance WLAN Security by Trevor Marshall
Used by permission
It shows the gain plot of a typical wireless PC card. If a PC card’s antenna were properly omni-directional, the red and blue dotted lines would look more like circles. Instead, the lopsided patterns you see are the reason why you have to aim your laptop in a certain direction in order to connect to your access point.
The MINI is a classic dipole and has the same gain in all directions.
2) Its polarization matches your AP’s – Most access points and wireless routers have external antennas that generally point straight up or at a slight angle. This yields a vertically polarized signal. Of course, WLAN PC card antennas provide a horizontally polarized signal because of the way they sit in your laptop’s PC card slot. The result is yet another obstacle in the way of optimum performance.
Since you can move the MINI around, you can orient it vertically – same as your AP / wireless router.
Performance
Theory is one thing, but if you’re going to shell out $25, you’ll want to see some real advantage, right? Figure 2 shows you the difference the MINI can make.
Figure 2: Performance comparison
(click on image for a larger view)
For my test I used my trusty ORiNOCO Gold PC card in my Dell Inspiron 4100 running WinXP Home, paired with an ASUS WL-300g Access Point and found a location where I had a marginal signal. The Chariot plot starts out without the MINI attached and you can see where I snapped it on about halfway through the run.
I also ran NetStumbler both with and without the MINI, but didn’t see enough difference to make it worth including the plot.
Closing Thoughts
If you have one of the cards that can use it, the MINI will definitely come in handy, especially if you’re highly mobile. $25 may seem like a lot, but if you’ve ever been in your room doing email sitting in the (empty) bathtub because that’s the only place you can get a decent signal from the hotel’s hotspot, I think you’ll agree it’s cheap at twice the price!
If you really are on a budget, you can always order the kit for $16, but – detailed assembly instructions nonwithstanding – most folks will be better off letting Aerialix do the cutting, soldering, and shrink tubing.