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'[EE] 2.4 GHz over water???'
2006\01\24@160239 by VULCAN20

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I am not knowledgeable with radio waves.  I was thinking of a project
using the Maxstream xbee Zigbee pro radios.  I need to send data from a
small rc boat to a larger full size boat  about 1000 M distance.
The big boat will have the ant about 3 to 4 M above water. The small
boat I would like to have as low as possible.  I asked an old ham radio
person about it and he said It would not work due to freq. and height
above water.
I e-mail Maxstream and all they would comment that it depended upon the
height above water and would not suggest min height required.
Any thoughts on this?

Any other radios that could be used?  Requirements: about 1000M over
freshwater, wave height less then  1M.,
the large boat would send signal to start data collection.  Then when
small boat had data it would send it back to larger boat.

Thank you very much?
John

2006\01\24@165154 by Enrico Schuerrer

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-----Ursprüngliche Nachricht-----
Von: "VULCAN20" <spam_OUTVULCAN20TakeThisOuTspamcharter.net>
An: "pic microcontroller discussion list" <.....PICLISTKILLspamspam@spam@mitvma.mit.edu>
Gesendet: Dienstag, 24. Jänner 2006 22:02
Betreff: [EE] 2.4 GHz over water???


{Quote hidden}

IMHO a question of the antenna height on the smaller boat above the waterline AND the height of sea waves. From the point of free space attenuation it's only a question of transmitting power and receiver sensitivity and the used antennas. A bigger problem I assume will be if the small boat is in a wave trough and so the direct visible line between the antennas is interrupted.

>
> Any other radios that could be used?  Requirements: about 1000M over
> freshwater, wave height less then  1M.,
>  the large boat would send signal to start data collection.  Then when
> small boat had data it would send it back to larger boat.
>

If you use a data transmission protocol with data protection even interuptions should not be a problem.

Enrico
OE1EQW

2006\01\24@231533 by Russell McMahon

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> I e-mail Maxstream and all they would comment that it depended upon
> the
> height above water and would not suggest min height required.
> Any thoughts on this?

>IMHO a question of the antenna height on the smaller boat above the
>waterline AND the height of sea waves. From the point of free space
>attenuation it's only a question of transmitting power and receiver
>sensitivity and the used antennas. A bigger problem I assume will be
>if the small boat is in a wave trough and so the direct visible line
>between the antennas is interrupted./>

__________

And there are going to be "Fresnel zone" issues (Google knows). The
direct and reflected waves interact. Antenna height above ground
(here, water) path helps heaps. There are calculators / algorithms
available that cover this BUT I'd say that if you had enough power to
work well with plenty of height above the water than it will still
work "somewhat" when your line of sight is in the wave tops. You would
need to reduce data rate, keep data packets short and have a robust
protocol. Whether this will work well enough for your application is
something only you will be able to determine.

I'd guess that giving the small boar aerial a bit of height should be
doable and liable to be useful.



       RM

2006\01\24@234103 by Peter Krengel

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2.4G WILL work IF the antennas can "see" each other. If water waves are too
high possibly interruptions could happen.

Using lower frequencies such as 70cm (433 MHz) would give a better security.

Peter
DG4EK





{Original Message removed}

2006\01\25@010042 by Peter Krengel

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Ooops....did I missunderstood your question? Did you like to set the antenna
of the small boat UNDER water?

That sure doesnt work. As somebody states earlier 2.4 Ghz (about) is der
frequency of resonance of the water molecules! Anyway, any high frequency
will not work under normal sea water (if you use destilled water it works).

Therefore in military (i.e. submarines) ultrasonic is used as a carrier
frequency. All what you need is two special under water speakers and
microphones (and of cause  transceivers). But there is one disadvantage
using this. As you have to transfer datas the usuable transfer rate will be
rather low.

So using any VHF oder UHF frequency will be the best way to solve the
problem.

Peter
DG4EK




{Original Message removed}

2006\01\25@090503 by VULCAN20

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As the subject line saud "2.4 GHz  over water???"  No, you did not
misunderstand, but others must have.
Thank you
John

Peter Krengel wrote:

{Quote hidden}

>{Original Message removed}

2006\01\25@132842 by Peter

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http://www.qsl.net/w4sat/horizon.htm

I think that you can take the antenna height of 1 meter but availability
1/2 (when the small boat is in a trough its horizon is zero).

Peter

2006\01\25@194143 by Gus Salavatore Calabrese

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There is more to consider than line of sight...
Fresnel effects will cut the signal down as well.
See
 http://www.winncom.com/glossary.aspx?term=23
http://www.connect802.com/wcu/2005/newsletter_050501.htm

Comments on 2.4 GHz through water
http://expertanswercenter.techtarget.com/eac/knowledgebaseAnswer/
0,295199,sid63_gci976435,00.html

Regards

AGSC

2006\01\26@085021 by alan smith

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I'm not sure if thats really true, other in the sense of..."seeing" the RF signal.  I've taken Xbee modules, put on the other side of the house (also done with some TI demo boards) so there is quite a bit of 'stuff' between them and they tend to still work pretty good.  True, that if you mount the module up high, the ability for them to see each other is better.  Sometimes it just comes down to simple experimentation.  

 For Maxstream to come and say...oh sure that will work.....its like any application, too many unknowns to predict if it will work reliably.  Best thing to do, no matter what you use, is to have the master ACK the slave devices to ensure that the data was properly received.
 
Peter Krengel <krengeldatecspamKILLspamgmx.de> wrote:
 2.4G WILL work IF the antennas can "see" each other. If water waves are too
high possibly interruptions could happen.

Using lower frequencies such as 70cm (433 MHz) would give a better security.

Peter
DG4EK





{Original Message removed}

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