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Wifi over water

Wifi over water

Wifi over water

(OP)
Hello, I want to try a point-multipoint link in 900MHz over water. I known about the problem of multipath and the implementation of circular polarization is not an option because the small angle. The good thing is that I can put one antenna over a Buildin at 100mts hi and the vessel is also hi (20mts) How long do you think I can rich with this cain of system? I want to use a omni over the vessel but then I can use another type of antenna over the buildin because the vessel´s way is alway the same and is straight.I hope someone can advise me before I through my money.

Regards

RE: Wifi over water

(OP)
Above 20dB over signal sensibility...

RE: Wifi over water

If you keep to 60% of the first Fresnel zone in standard atmo conditions (and there are no obstructions between building and ship), I can see 30km without much issue with a 20dB fade margin (assuming a -90dBm receiver sensitivity and a 29dBi gain antenna at each end... lower antenna gains, as necessary, and add it to the base transmit power of 0).

With full details about what you intend to use I can provide more detailed numbers.

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Wifi over water

(OP)
I want to use a 8 dBi gain antenna over the vessel and a 14 dBi Yagy antenna. I ´m going to use ubiquiti xr9 with 28 dBm of output....What about multipat...??

RE: Wifi over water

(OP)
Do you known about a more directional antenna on 900MHz? I can´t find anything over 14 dBi

RE: Wifi over water

There is a phenonmenon called "ducting" that might get you better propagation if your antenna was not on the building top, but lower.

www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

RE: Wifi over water

biff,

Wouldn't ducting be seasonal/unreliable (as well as being more land-based/shoreline in nature rather than beyond the coastline)?

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Wifi over water

(OP)
Thanks everybody for the advise. I´m interesting in "ducting" how could I known which is the best hi to install the antenna. It is a good choise to use a 900MHz system entead of a 2.4GHz or 5.8GHz?? what about freznel zone or multipath...I guess I will learn a lot trying to do this...

RE: Wifi over water

Ducting may not be reliable. It's a bending of the signal due to atmospheric conditions. Like Ham radio energy hopping.
I'd look for alot more info on it before venturing that way.

I think that 18 dBi antenna will help you. 900 Mhz is probably better than the higher frequencies. The loss between your two antennas in your link will be typically lower at 900 mhz by the ratio of the physical sizes of your antennas on the building plus add 20*log(fhi/900mhz) ratio(assumes omni antenna on the ocean and formula relates to effective area of omni antennas).    

RE: Wifi over water

(OP)
Hi Higgler. I have to tell you that I sign in here because I read this from you...
"The circular polarization thing works worst mathematically at around 6 degrees incidence angle since all of the vertical polarization energy is absorbed at that angle by a flat ocean. Hence if you send circular you receive horizontal polarization over the water at that incidence angle.One thing I've often thought about but haven't seen, is to have a receive antenna aboard ship for a program such as this using two antennas atop each other. Combined them into a magic tee (zero/180 degree outputs) to have sum and difference outputs. If you can point the null of the 180 degree output properly (between the tranmitter and the ocean), then the energy bounce off the ocean will always help one channel and always hurt another channel of the magic tee output, hence dual receiver front ends to detect the highest signal would stop multipath fading. I believe the antenna separation must be large if the transmit antennas in this system are close to the water. It works best for picking up low flying transmitters approaching ships that pop into and out of dead spots due to multipath on a calm ocean day. Antenna diversity would help too, but not as reliably at the magic tee, or so I think. Proof is always in the measurements, and sometimes in the paperwork. I've seen alot of trees killed for nothing by useless ink.kch"

I´m gonna star with an omni 8dBi over a small vessel and a parabolic of 15 dBi over a small buildin. I guess with this I´ll have an idea...Talking about multipath do you think that is a better option to use 900MHz not only because of the losspath  but also the absorve coefficient  from the water at this frequency?
regards....

RE: Wifi over water

I don't know if you can "count on" the ducting phenomenon to be there when you need it.  Never the less, if you are using a wifi card (especially one with 802.11N multi antenna mimo capabilites to handle multipath and channel perturbations), it sounds like a lower antenna would greatly extend the range in the sumer time.  In fact, a higher antenna might have the signal "bounce off" the ducting layer and miss the boat entirely, as I gather.

www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

RE: Wifi over water

(OP)
Guys after try with the omni over the vessel I would like to try with a traking antenna system. I known that there is a lot of this for aeromodelling. Can you advise me of some system ?

RE: Wifi over water

The temperature inversion layers associated with "ducting" of (typically VHF/UHF) radio signals normally occur at altitudes well above 100m.

For example, distant FM broadcast stations can often be heard in the Spring mornings on your car radio, and their broadcast antennas are often installed on top of very tall buildings, or very very tall towers.

What sort of signal is being carried by this radio link?

Are we talking about the unlicensed (YMMV) 902 to 928 MHz band? Is the base station in a large city (a building was mentioned)? If you aim a high gain 900 MHz antenna into a coastal city from offshore, then you're going to pick-up every wireless speaker, wireless headphone, older cordless telephone, wireless intercom, etc. And this environment may change from moment to moment.

If this radio link is for data, might it be simpler to use a mobile data USB stick (or smart phone), one with a socket for an external moderate gain antenna, and access the commercial data network. A bare device can reach several kilometers, add an external antenna and the range could be out to the horizon (maybe).


     

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