rf communication recommendataion

Hi all, I need RF link to communication from sea to shore covering a distance of approx. 20km. I need an RF link which does not impose much
conditions on the antenna size( I can have only a 50cm antenna). The link should work with an omnidirectional antenna. Please recommend any RF equipment/product that may cover a range 20-30km. The speed can be in 192000bps and above. Thanks in advance. Kkrishna.
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kkrish wrote:

There are a few questions that arise which you have not pre-answered in your posting.
1. Which country are you wishing to implement this link in. Different countries have different regulatory regimes for wireless communications.
2. Why would your antenna size need to be limited to 50cm and why does it need to be omnidirectional. If the positions are fixed a directional Yagi can be much more efficient and require less electrical power at each end.
3. With your requirements, you may need to look at obtaining the appropriate operating licencing from the regulatory authorities. This will resolve whether you will be in the VHF or the UHF ranges (both could do it but the allowable power limits might differ).
When you can fill us in on those aspects there may be some suggestions about what equipment you could use for the RF links.
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On 09/26/2010 04:15 AM, Paul E. Bennett wrote:

I don't know how much he could count on diffraction -- without it, he'd need to elevate his antennas, possibly significantly. I get 32 meters high if the other one is at ground level, or both at 8 meters.
8 meters isn't much, unless you're on a row boat or a buoy -- and he didn't say.
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You are right . I will be on a boat at the Txr. end. I can have the receiver antenna with more length. Licensing may not be a problem but we need reliable transmission.
Thanks in advance.
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kkrish wrote:

Intriguing why you think licensing may not be a problem. Apart from truly international waters I don't know anywhere on the planet where licensing would not be a consideration (for other than the short range licence free bands).
So far we have very scant information from you. We know that it is data at 192000bps or more (but how much faster do you expect?). We also know that the distance is expected to be approximately 20km. We have been told your antenna can only be 50cm in length (but not the reason why) and that it is expected to be omni-directional (again why is not explained). The transmitter is on a boat.
So, in order to get some real help a little more information is needed.
1. World Region which regulates the spectrum in your area.
2. Data packet size and quantity to be transferred.
3. Maximum error rate you can live with.
4. How much power is available for your transmitter (if you are on a boat this may be quite limited).
5. Where the other end of the link is located (on shore?) and what height restrictions you may face there.
There will be more questions but they will become clearer when you have filled in some more of the story for us.
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On 09/27/2010 11:58 AM, Paul E. Bennett wrote:

Somalia? Drug running?
But yea -- most places on the globe you'll run afoul of the local spectrum allocating agency if you just pick a frequency at random and start transmitting.

And we still don't know how high of a mast he can put on the boat, or if he can use an antenna that's omnidirectional horizontal but has gain from compressing the vertical beamwidth (which presumes the boat doesn't rock much).

Both regulatory and expense -- if his power restrictions are severe enough that he absolutely positively needs line of sight then he needs a tower that's 32 meters high at least, and while that's quite practical it's not necessarily cheap.

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Tim Wescott
Wescott Design Services
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First, Thanks for your replies.... I am not from Somalia and I am not doing anything bad. We can apply for permission from our country for the license. That is the reason I mentioned no need to worry about license right now. We need reliable data transmission, 1/10000000 will be a better error rate we would like to have. The receiver will be at shore and the height of the antenna can be higher.
Thanks in advance.
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And I can have a solar panel that can serve the power may be upto 10W.
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