Omni antenna help please

Keep it clamped to the mast. It would offer better lightning protection.

Just curious, is it mounted at the very top of your mast or on the side?

The antenna is clamped to the side of the mast on a 5 foot mast, on a chimney mount. The antenna is well above the chimney that we don't use any longer.

DTC wrote:

snipped-for-privacy@here.com hath wroth:

As I understand boats, a mast is something that is vertical. The antenna is also suppose to be vertical. So, I presume you have it laying flat against the main mast held in place with anything from bungi cord to ty-wraps. Perhaps there's a yard arm between the antenna and the mast? Perhaps it's not a mast but something else? Perhaps something more descriptive than an ambiguous one line description would be more useful? If you can't describe it, make a sketch and post it to some web pile. Better yet, a photograph.

Doesn't really matter. If the mast is grounded, the metal base on the antenna should be grounded. Unlike HF radios, at 2.4GHz, it's not terribly important to ground the base as the internal counterpoise (ground plane) will take care of providing the necessary ground plane under the antenna. In most cases, the 2.4GHz omni metal base is just there for ease of mounting.

There is one exception. It's possible on a large vessel to create a ground loop through the mast and back down the coax cable of the antenna. If this is a problem, then just insulate the antenna base from the mast.

Hint: Please learn to operate a text editor and kindly trim your quotes. I just hate reading my own rants twice.

Which is terribly bad advice. Tie down the stern and you lose the boat's ability to ride with the waves, wind and currents. The stern gets caught facing into the waves. A wave coming over the transom can swamp and sink it. No thanks.

I went with an 8db omni and it's been great. It does, however, have some trouble when rocking more than a few degrees. The 'donut' of coverage pivots enough to lose the shore access points. And the closer it is to shore the more pronounced the effect. That and if you pickup "too many" shore APs it can degrade your throughput. I can only image a 14db unit would be *worse* at both noise and coverage when rocking.

Well, that demonstrates how little I know about sailing. It seemed like a good idea, but I guess not. I stand corrected.

Yep. However, I'm still of the opinion that a directional antenna with some reasonable (8-10dBi) gain is the way to do it. For example, the common biquad has about this much gain, with a 60 degree beamwidth in both vertical and horizontal.

That will take care of quite a bit of rocking and rolling, but will not do anything for swinging at anchor. You also have to aim the antenna which means you have to have some clue where the shore station is located. I'm not too worried about interference from shore, but there's going to be plenty from other boaters in the harbor with similar setups. The directional antenna at gets rid of perhaps the interference from behind and to the sides is an improvement, but not t total solution.

Jeff,

Should my 40" omni be perfectly vertical? If it is not perfect would it cause problems? I seem to remember you stating that in a previous post. Thanks.

snipped-for-privacy@here.com hath wroth:

Yes.

I did mention that in at least 3 postings. I suggest you go back and re-read what I scribbled. The problem is that your 40" vertical antenna has a -3dB vertical radiation angle of about 8 degrees (my guess). It also has a downtilt of -3degrees. That means that most of your signal is located between 1 degree above the horizon, to 7 degrees below the horizon. If your vessel rocks more than this, the signal will literally disappear. What you'll see are wide variations in signal strength as the vessel rocks and rolls. If the signal is weak to start with, it will just disappear.

This is why a lower gain antenna is better. It has a wider vertical radiation angle and can therefore tolerate more movement from the vertical. This is also why I recommended a directional antenna. It has a VERY wide radiation angle and can tolerate considerable rocking, if you can figure out where to aim it.

If you want to see the action, fire up Netstumbler and produce a graph of the signal strenght. I predict wide variations.

Now, my turn. You keep asking essentially the same question over and over again. You're also ignoring my requests for additional info, such as the antenna height above the water, and the manner of mounting. You're apparently not absorbing what I'm saying. I suggest you find a local consultant or someone experienced with marine radio electronics and have them do the installation. If you don't want to do that, just re-read the dozen or so messages I've posted on this topic.

I appreciate your reply and apologize for being repetitive. The antenna is on a house not a boat so I will make sure it is perfectly vertical.

Also, would the super cantenna be a good choice of a directional antenna? Thanks.

Jeff Liebermann wrote:

You should always try a simple parabolic reflector first. You can make one out of cardboard and tinfoil in 30 minutes. Google for freeantennas.com

I will do that, thanks. BTW, doe3s a Linksys wrt54g transmit in vertical or horizontal? I assume it's vertical but I am no expert, thanks.

"Travis McGee" wrote:

snipped-for-privacy@here.com hath wroth:

Sigh. I give up. I've only mentioned boat in the last 10 or so replies and you wait until now to say something? You also didn't bother to supply the antenna altitude above the ground after I asked 3 times. I don't have a clue you're trying to accomplish. I'm getting rather tired for the one line repetative questions and repetative answers. As I previously suggested, please hire a local consultant with some wireless experience. I can't design your system with what little information you're providing. The good news is that since your not on the water, the -3dB downtilt will be rather useful for your unspecified height antenna (it it's fairly high off the ground).

Good choice to do what? Figure on about 8-10dBi maximum gain at best. A 6dB increase in gain is double your distance. Do the math.

Same reason you never see, well...not after the radio department figures it out, that mobile data antennas are a simple unity gain stub.