Jul 222009

WiFi AntennaThe importance of the WiFi antenna is oftenoverlooked. Many yachtsmen just use the antenna their system came with. The capability of an antenna to boost a signal is expressed in decibels (dB). An off the shelf short “stubby” antenna will typically provide a 3dB gain. As with the sensitivity, each 3dB step provides a doubling of the range. Additional gain can be achieved either by going to higher quality antennae, or by focussing the signal. In the latter case, rather than transmitting and receiving in a full circle as with the “omni-directional” antennae, one can opt to focus the radio beam into a narrower segment using some form of “directional” antenna. Think of this as adding a reflector to the back of a lamp. More of the available light/radio energy is directed into a specific direction. For our dialogue restricting the available energy into a 120-degree arc significantly increases the range.

Boats are not a very stable platform. At anchor they can swing through a large arc due to tide, wind, and wakes. In port (or at a quiet anchorage) the motion is much more limited.

Our customer Ewoute Mante (the author of this article): wrote: 95% of the time we used a directional antenna that covers a 120 degree arc and boosts the signal by 15dB. We found that narrower directional beams cause too much signal interruption when the boat moves and thus looses alignment with the shore-based Access Point. It is perhaps 5% of the time that we use the omni-directional antenna. We take it out when the boat swings too much for the directional antenna to remain locked into an Access Point. The omni-directional antenna has a shorter range and thus shows fewer APs.

Marine-grade omni-directional antenna: SKU A8oM

Positioning of AntennaThe positioning of the Antenna is very important:  Anybody that has used a traditional AM/FM radio will know that rotating a radio just a couple of degrees or moving it relative to large metal objects can have a dramatic effect on reception (and similarly transmission).  Ewoute Mante (aritcle author):  We typically have the antenna inside the boat, which makes it easy to aim the directional antenna when we arrive in a new port. Usually, on arrival we do a quick scan by rotating the antenna over a 30-degree arc, checking what Access Points we see. We repeat this step until we have completed a full circle. The entire process usually takes less than 2 minutes. Under marginal conditions (i.e. when we failed to pick up a good signal), we usually move the antenna on deck, or even attach it to a boathook that we point up through a hatch and then rotate to aim the antenna in the required direction. This is a pretty rare occasion.

The omni-directional antenna also usually starts it “work” below decks and only moves above decks when the need becomes apparent. We added a special loop at the top, that allows us to suspend that antenna from the boom or if need be a halyard.

Permanent installation: Pros & ConsWe do not like permanent installations for three reasons:

  1. Most permanent installations imply a fixed antenna positioning
  2. A permanent installation requires a marine grade solution. Not only does it make the unit itself more expensive, the combined cost of fittings, cables, glands etc. all add up.
  3. WIFI is a fast moving field. Take heed from the lessons of cellular phones: In the late 90s some boats added masthead antennae for their cellular phones and docking stations at considerable expense. Most of that technology became obsolete very quickly…
 Posted by at 7:07 pm Antennas, Antennas Tagged with:  Add comments

 Leave a Reply

Copyright © 2004 - 2017 Data Alliance lnc. All Rights Reserved