Well for right now, feel free to check my about me page on my other blog. Thanks!
— Mike
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Well for right now, feel free to check my about me page on my other blog. Thanks!
— Mike
Mike's Blog 
Been surfing for a diy omni directional wifi antenna with a usb connection. Going to use it on my boat, so a directional (cantenna or similiar) won’t really work due to the rocking that occurs in most anchorages. Found anything?
Well a non-directional antenna would have the same issues as a directional one. A non-directional antenna is non-directional in the horizontal plane,. But in the vertical plane signal strength drops, and approaches zero at 90 degrees. (straight up).
It has been my experience that with a high gain directional antenna you are good for as much as 15 deg. off axis. So that would give you as much as a 30 deg. total “spread”.
I’m no boater, but any more than a 30 degree rocking of the boat might be a little scary, let alone trying to use a laptop.
Honestly I don’t think the rocking would hurt it too much. Does a boat really rock 30 degrees off of vertical in an ancorage? That seems like a lot.
A high gain directional antenna has what is called a “half-power beamwidth” of around 20 degrees, which means at 20 degress off axis you will only loose 3 db. So if a Cantenna has 17 db of gain (like my design) then 20 degrees off axis you are still going to have 14 db of gain.
If it were me, I would just give it a try, it just might work.
Thanks for the education on antenna theory. I did not realize the directional antennas had that wide a cone.
The complicating factor is at anchor there are 3 axis of motion. The first is vertical, tide changing the elevation of the boat. It is so slow, I don’t see it as a problem. The second is the rocking that you mention. The third is swinging around the anchor due to wind/tide/current changes. Think moving like a pendlum in the horizontal plane or orientation of boat rotating around the compass card. Unless the current and wind are directly on the bow (1 in 10 chance), at anchor my boat (many others are similar) will slowly swing through 30-45 degrees hunting for equilibrium. It is mostly this swing, combined with rocking from passing boats, that I think makes the use of an omni much more practical than a directional antenna.
Oh yes, I see your issue now. For some reason I was thinking you were moored to a dock. But with an anchor is different!
You are correct, you need an omni antenna. I have an omni wifi antenna design rattling around in my head, but I need time to experiment and such. Hopefully I will get to that soon.
— Mike