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enlace de wifi kilometros 500 ??

Enlace Wifi de 500 Kilometros ??
#1
Hoy he encontrado un articulo algo distinto a lo habitual y me ha llamado la atencion que dicho proyecto se basa en el Rebote de las señales de Wireless en la Ionosfera para intentar conseguir dicho enlace de 500 kilometros.

Dicho Proyecto esta en Ingles.... pero creo que merece la pena echarle un vistazo:

Informacion obtenida de http://wiki.whatthehack.org

Preliminaries

Oftelsat, MCCH: http://fundmcch.com.ec (trading as brothers) direct involved as partners together with the IICD (enabling ICT in developing countries) http://IICD.org, initiated the following pilot in Ecuador, Latin-America----- Please look at the end of the article for latest development! End of october.

note: The format we use is not 802.11/wifi. Its the IP traffic over wireless thats important to us. Thats what we intend to do. A wireless long distance gateway to the Internet (com. Karel Fassotte)

The Article

The wireless solutions we see today are a product of western industrial society. They were developed for fast mobile communication in the urban society. Wireless is nothing new. Radio recievers have existed for over 100 years now.

Available solutions are:

G3 mobile phone and Internet.
G4, Wifi (802.11 a/b/g) is good for Line-Of-Sight, max. 50 km, with good engineering.
Wimax (802.16 a) promises more, Near-Line-Of-Site, maximum 50 km.
Packet switching (A)X-25 VHF and UHF networks.
Satellite IP. Nearly everywhere.
But what is the MISSING LINK?

Beside satellite connectivity, there is no other solution for the rural, far off regions!

Oftelsat is a small group of radio and computer engineers, working in the south of this planet (Ecuador). Together with the IICD - International Institute for Communication and Development [http://:www.iicd.org] and MCCH [http://www.fundmcch.com.ec ] They're dedicated to finding connectivity solutions for social and economic development in rural environments.

Today Karel Fassotte explained, how he and others solved the issue to bring up a non-expensive voice, fax and data link in Ecuador rural territories using WI-NVIS (Near Vertical Incidence Skywave).

The used Frequency band is 2í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“10 MHz Shortwave (not microwave).

[Imagen: Ionosphere-1.jpg]

Radio waves propagate in a straight line of sight (LoS), like a laser. If the signal is blocked or severely attenuated, the link is broken. No connection.

shortwaves 2-30MHz are still very interesting!

Lower frequencies in the 2 to 30MHz. Have special properties.

The radio waves of shortwaves, may be reflected back to the earth at a high altitude, 200km layer, in the so called í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í¢â‚¬Â¦íƒÂ¢í¢â€šÂ¬í…“IONOSPHERE‿.

To travel a long distance, the signal must take off at a low angle from the antenna, -30 degrees or less. This is so it can travel the maximum distance before it first arrives at the Ionosphere. Long gaps before the signal returns to earth í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ the part in between this and the end of the ground wave is the so-called Skip (or Dead) Zone. The distances that can be reached are some 1,000km and more with Skip Zone gaps. Our goal is 0 to 500km, without gaps!

[Imagen: Ionosphere-2.jpg]

To travel a local - medium distance, the signal must take off at a HIGH angle from the antenna í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ typically 60 í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ 90 degrees! This returns from the Ionosphere at a similar angle, covering 0 í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ 500km. It thus fills in the Skip (or Dead) Zone í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ like taking a hose and spraying right up, the water will fall in a cetrain round area.

What is now most important?

-HIGH angle of radiation from antenna
-Minimise ground wave, as it will interfere with the returning skywave
-Most importantly, CHOOSE THE CORRECT FREQUENCY BAND í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ go too high in frequency and your signal will pass
through straight into space!
Choosing the RIGHT frequency:

The Ionosphere í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ D, E, F1 & F2 layers

D and to a lesser extent, E layers attenuate and absorb signal
Best returns from F2 layer
At any one time we need to know the frequency of the F2 layer í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ The Critical Frequency or foF2
Optimum frequency for NVIS work around 10% below this

[Imagen: Ionosphere-3.jpg]

NVIS frequency and time:

In practice, highest NVIS frequency can reach 10 MHz band. Lowest can go down down to1.81 MHz band. í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í¢â‚¬Â¹íƒâ€¦í¢â‚¬Å“Higherí­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¾íƒâ€ší‚¢ frequency band during day, í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í¢â‚¬Â¹íƒâ€¦í¢â‚¬Å“Middleí­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¾íƒâ€ší‚¢ frequencies afternoon/evening, í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í¢â‚¬Â¹íƒâ€¦í¢â‚¬Å“Lowerí­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¾íƒâ€ší‚¢ frequencies at night. Frequencies also affected by time of year and period of sunspot cycle. For best results, these three different frequency í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í¢â‚¬Â¹íƒâ€¦í¢â‚¬Å“bandsí­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¾íƒâ€ší‚¢ required.

Also F2 is the critical frequency:

The Critical Frequency is the key to successful NVIS working. The Critical Frequency (or foF2) is the highest frequency at any one time that a signal transmitted vertically will be returned to earth. Anything above this passes into Space. As they are interested in vertical signals for NVIS, then the value of the Critical Frequency (foF2) at any one time is of great importance to them.

But how to find or estimate foF2?

BY PREDICTION:

Real-time web information from Ionosondes
Websites offering Critical Frequency predictions: í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ RAL STIF, IPS Euromaps
Software Propagation prediction tables or similar printed material
Rule-of-thumb:- í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í¢â‚¬Â¹íƒâ€¦í¢â‚¬Å“higherí­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¾íƒâ€ší‚¢ band by day, í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í¢â‚¬Â¹íƒâ€¦í¢â‚¬Å“middleí­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¾íƒâ€ší‚¢ band afternoon/evening transition, í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í¢â‚¬Â¹íƒâ€¦í¢â‚¬Å“lowerí­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¾íƒâ€ší‚¢ band nightime

[Imagen: Ionogram_from_EISCAT.jpg]

The most likely bands:

In practice, 8 MHz (35m) usually í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í¢â‚¬Â¹íƒâ€¦í¢â‚¬Å“highestí­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¾íƒâ€ší‚¢ band
4 MHz (80m) next lowest
1.81 MHz (160m, í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í¢â‚¬Â¹íƒâ€¦í¢â‚¬Å“Topbandí­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¾íƒâ€ší‚¢) the lowest
80m and 160m strongly affected during the day by absorption from the D-layer, plus noise at night and varying
times of the year
Transition frequency around 5 MHz!
e.g. a realtime ionogram:

[Imagen: Realtime_ionogram.jpg]

[Imagen: MUF_LUF_MOTS.jpg]

Predicted signal levels:

[Imagen: Predicted_signal_levels.jpg]

The best usable frequencies:

[Imagen: Best_usable_frequencies.jpg]

Next Question: What kind of Antenna is here to use?

Need high angle (60-90º) radiation for NVIS
Vertical no use í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ predominantly low angle
Half wave dipole at 0.5 wavelength produces low angle radiation, BUT, if lowered to 0.25 wavelength or below,
produces high angle radiation !
Not too low, though í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ some earth losses. A reflector wire or earth mat can reduce this.

[Imagen: Antenna-1.jpg]

The antenna, the key to be successful:

The right angle and direction is very important! It always is, here it is a little bigger!

Horizontal dipole radiates at low angle radiation, it must be half (0.5) a wavelength above ground.

Lambda 40 = 20meters!

In the case of the lower bands such as 80 and 160m, this would be pretty high and big!

Horizontal dipole at íƒÆ’í†â€™íƒÂ¢í¢â€šÂ¬í…¡½ Lambda altitude:

[Imagen: Antenna-2.jpg]

The vertical opening depends on antenna height:

- If the height of the dipole is lowered, the angle of radiation becomes higher and the low angle radiation
starts to disappear

- The optimum amount of high angle radiation is obtained at a quarter- (0.25) wavelength above ground

- Going lower than 0.25 causes efficiency loss
- In practice 0.25 í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ 0.15 wavelength heights used for NVIS

High angle radiation í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í¢â‚¬Â¦íƒÂ¢í¢â€šÂ¬í…“Straight up- Straight down

[Imagen: Antenna-3.jpg]

What about the antenna bandwidth?

The dipole is essentially a single band antenna
There are also a couple of special higher-gain single band NVIS antennas í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“
Dipole with reflector
The Shirley
The Jamaica
(thought, that the pics from each type is not needed here)

Multiband antennas:

As mentioned earlier, at least three different frequency bands are needed for successful 24 hr NVIS service and so multi or wideband antennas are used. Simple ones include long wire, inverted-L, Shallow (120º) Inverted-Vee Doublet with open feeder, full-wave low (0.15-0.25λWink horizontal loop (reflector could also be used below this) . Other multiband antennas can be used, key is the correct height of the antenna.

Not only the correct angle of transmission TOA but ALE:

ALE : Automatic Link Establishment
ALE scans and tests sets of frequencies í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ usually in several bands - for a particular path or net until it
finds a frequency that will support communications over the path.
Each radio in an ALE net constantly broadcasts a sounding signal and í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í¢â‚¬Â¦íƒÂ¢í¢â€šÂ¬í…“listens‿ for other sounding signals
generated by other net members
Analysis of these signals by processing determines the best frequency for communication at the time and this
frequency is then selected automatically for operations
Here PC-ALE, a software program written by Charles Brain, is the solution (screenshot):

[Imagen: Pc-ale.jpg]

NVIS summary:

Covers 0 í­Â¢íƒÆ’í‚¢íƒÂ¢í¢â€šÂ¬í…¡íƒâ€ší‚¬íƒÆ’í‚¢íƒÂ¢í¢â‚¬Å¡í‚¬íƒâ€¦í¢â‚¬Å“ 500Km using High-Angle (50-90º) Skywave
Choice of Correct Frequency Band just below the Critical Frequency is most important.
Antenna must be horizontal, not vertical.
Antenna must be on a correct altitude, between 0.25 and 0.15 of a wavelength above ground (antenna aperture)
An NVIS antenna has omnidirectional radiation
Multiband antenna (at least three bands) needed for 24hr NVIS coverage
And the digital link???

First some more about mother nature.
Shortwave propagation the gift of nature is not easily predictable!
It depends on our sun, the solar activity. Particals and radiation hit the upper atmosphere of the earth,
charging the gasatoms, giving it the property to reflect certain frequencies.
The sun is very dynamic, but has some cycles in her life! 11 year shift, from higher activity to lower activity
(right now 2005/2006)
Cycles Solar activity:

There is off cource a day and night cycle
Also a seasonal cycle (angle of incedence)
Oftelsat start their pilot in Ecuador (see beginning of the article), and the most important specs were the following:

Establish a digital link, if possible 24 hours a day.
First digital voice and audio
Data transfer, FTP like.
Gateway to internet
Remote -control of the transcievers and pc (desktop)
The used COTS-equipment was the following:

Transciever: IC706MKIIG, shortwave, VHF,UHF transciever. Modified to transmit and recieve from 1Mhz. - 470Mhz.
Powersupply: a computer (switching) powersupply, 13,8volts, 20 amps max. modified to charge a car battery.

IC706KMIIG

[Imagen: Transceiver.jpg]

and more COTS-equipment:

A T2FD broadband antenna. 3-30Mhz.
A duoband dipole, 4 and 7Mhz.
A desktop P.C.
Simple soundcards.
A digital voice and data modem ARD9800, capable of 3kbs, using OFDM, multitone.
A car with build on antennatuner longwire and whip antenna. Also equiped with an ARD9800 modem and IC-706

Longwire on the car with tuner (scheme):

[Imagen: Car-antenna.jpg]

And here a picture of the mobile unit from beside viewed:

[Imagen: Mobile-unit.jpg]

And here (just for fun) a real picture from the mobile unit:

[Imagen: Mobile-unit2.jpg]

The used software was Digital Radio Mundial multimedia, digital waveform software. They decided not to transmit with a wider bandwith than the 3Khz. Maximum speed 5.6kbs. Q15X25 Packet software (linux) 15 sub-carrier X25. And they want the Q15X25 to run IP traffic and gateway this to Internet. Speed also 3kbs.

The link maintenance was realized with PC-ALE software, mil.std. 188-141 with kind permission of Charles Brain (the author). Because of lack of interest in the experimenters world, he did not have the linux sourcecode anymore. With this software, a multimedia Laptop and an inexpensive transceiver, it is possible to successfully enter an ALE network.

So what happended in real life with this stuff?

First tests, taken on 7 and 8juli 2005.
They first established a digital voicelink with el Mirador, close to the town of Quinide in Esmeraldas, at some
100km distance
After that they've established a digital link between Esmeraldas and Guyaquil. It works!
They aimed at 24 hours service capacity. This was not imediately achieved. Only parts of the night en day. This
was due to the wroung transmission angle TOA.. The antenna was to low.
'Digital voice

The digital voice unit worked fine. The quality cannot be compared with the analoge signal. What a difference!
The mobile unit could recieve well but transmission quality was not enough. The whip antenna, 2meters long, did
not a good job.
'In the last trails we did end of juli, we repaired the horizontal whip that was burned and could stay connected, mobile, in the whole of Ecuador, the south of colombia and the north of Peru, more than 1000km. We were driving our mobile from the city of Riobamba in the middle of the country to Quito, the capital. We connected to every station in the HC-Network (amateur radio emergency network)!!! The mobile unit'

The longwire antenna worked very fine. The car when parked could setup digital voice communications within 10
minutes.
Recieving was possible, mobile and over hundreds of kilometers.(see above for update)

The digital data transmission

Non IP data were succesfully transmitted over 350 km. Speed: 3kbs troughput.
DRM transmissions, voice and data were also succesfull 3.5kbs.
Q15X25 packet at 3kbs, did not function, because of some bugs in the software.
ALE did not work well, because of interfacing problems.






[edit]So what happened next
Now end of august 2005,we got the PC-ALE running and linking. The problem we had was related to a hardware problem in the interfacing. We resolved this and all is working perfect. The mobile unit is capable of participating mobile in the network

But in view with all this problems to solve in the future, they have still an link over 350 km up and running quite well.

THE FUTURE

It is surely not a mass solution for bigger cities etc.
Their goal is to create a radiomodem that is capable of 64Kbs in a multislotted system, using more than 1
radiochannel at a time (10).
The plan is to use a SDR (software defined radio)
Time critical aplications are not always possible!
Several digital voice channels are possible.
DSP will be a natural choice for the radio. Easily reproduced and updated, with the same hardware.
This development has to replace the Icom 706
A transparant IP gateway, can easily provide sufficient bandwith for smaller, rural, far off telecenters, These
centers are well served with this wireless solution.
Operational costs are low.
Next phase will be an ip gateway to the intranet/internet. Planned for the end of 2005.
(Update Now august 2005, we are already implementing these services in the link).

Third phase is the implementation of a SDR multiple carier system and system integration under Linux. Planned for 2006.
CONCLUSIONS

NVIS, Near Vertical Incedent Skywave, automated shortwave IP data transmissions, are feasinable at costs less
than satelite.
Operation has always been dificult because of the many factors involved, maintaining a link. Now with
possibilities of digital techniques, systems can be automated and transparent for the user, f.i. an ethernet
gateway.
Bandwith that may be obtained are some 1bs /hz, using more sofisticated modulation and demodulation (adaptive
sequential coding) can optimize link efficiency.
3bs/hz should be obtainable.
Digital mobile NVIS, within a cell structure of more dan 2000km diameter, is available (with good antenna engineering).

What do OFTELSAT want???

The job we are doing has to be done.
We are looking for reenforcement!
Involve more brains
Keep it an open enviroment, GNU
We are interested in integrated solutions for development and communication
If you're interested feel free to contact Karel as follows: We notice a lot of people reading the page, but only few people, participate. karel fassotte karel@oftelsat.com karel.fassotte@gmail.com

Latest results 22-10-05 We still have some problems with the link. Its not open 24 hours a day. We have the ALE working, but the antenna system is not optimal. The signals are recieved in Atlanta US well, but in Esmeraldas not always. The vertical antenna seems to be to low now, < 50 degrees. MCCH has asked us to implement 2 more stations in the province of Esmeraldas. Installation should be finished in december 2005. (karel fassotte)

Please see also the pages of our partners: [http://www.IICD.org ] IICD - The International Institute for Communication and Development (IICD) assists developing countries to realise locally owned sustainable development MCCH [http://www.fundmcch.com.ec ] organisation of cacao farmers in Ecuador,

(eof, and i need a new pair of fingers. pls excuse my bad english, and the sometimes bad build sentences =) ...)

References
http://inventors.about.com/library/weekly/aa121599a.htm
Zero13

"Así como el hierro se oxida por falta de uso, también la inactividad destruye el intelecto.." - Leonardo Da Vinci

Síguenos en TwitterYoutube

Responder
#2
en 2'4 ghz va a ser q no , se podria por ejemplo mediante un convertidor de frecuencia pasar de 2'4 ghz a 7 khz o 40 metros? para asi conseguir rebote en la ionosfera?¿ pq a la frecuencia de 2'4 ghz el rebote se pasa la ionosfera por donde termina la espalda Big Grin

por cierto

http://www.zero13.net/foro/viewtopic.php...highlight=

Sad
Responder
#3
La conexión usando la ionosfera de rebote, es una buena opción, pero no esta estandarizado y tan solo existe esa investigación en marcha.

Puede ser demasiado complicado realizar algo con eso, tendriamos que hacerlo todo, incluyendo software para la conexión de los pcs.

Veo mas viable la opción de 2,4 Ghz con visión directa. Pero en un futuro, quien sabe...?
Responder
#4
Si.... yo no lo veo realizable todavia y menos con nuestros conocimientos y medios... quizas me equivoque... pero bueno, lo veo realmente dificil.

He puesto esta info porque la he visto interesante Wink ... solo eso.
Zero13

"Así como el hierro se oxida por falta de uso, también la inactividad destruye el intelecto.." - Leonardo Da Vinci

Síguenos en TwitterYoutube

Responder
#5
hombre, como he leido x ahi arriba, a frecuencias mas bajas (pocas decenas de khz) se ha conseguido tanto rebotar en la ionosfera como en la luna... pero, a 2.4Ghz me parece que va a ser que no...
Responder
#6
Simplemente para frecuencias por encima de 50 Mhz no existe rebote en esta capa. Las señales la atraviesan
Responder
#7
Hay un famoso colega que hace rebote lunar en 1.2 Ghz, por tanto en 2.4 es posible, pero hay que enfasar antenas y usar potencia (mas de 100 watios).

Lo del rebote ionosfera, pues apartir de 50 Mhz normalmente no es posible pero en ocasiones se presentan condiciones de propagación que si lo permiten, por ejemplo yo he mantenido comunicacion perfecta y con muy poca potencia (1 watio)con Canarias (yo vivo en el norte de España), es decir he mantenido comunicacion a 2000 kilometros, esto lo hice por rebote en capa E, en los meses de verano es habitual estos tipos de reflexion aunque duran muy poco tiempo.

Estos dias la nasa a anunciado unas lluvias meteoricas que permiten la reflexion de las ondas radioelectricas a mucha altura, este es otro metodo para alcanzar comunicaciones intercontinentales en frecuancias altas.

Pero lo nornal es lo que os digo, que por encima de 50 mhz no haya reflexion, por eso las comunicaciones con los satelites o por ejemplo con la famosa estación internacional espacial (iss) se hacen a frecuencias algo elevadas. Por contra a frecuencias mas bajas si se produce reflexion y es posible comunicar por ejemplo con Australia o cruzar el Atlantico sin ningun problema.

El mundo de la RF es apasionante...
Responder
#8
A ningon fabricante se le a ocurrido poner un punto de acceso en la estación espacial??? Tiene órbita geoestacionaria o varia?.
Lo digo porque seria muy interesante de ser posible.
Responder
#9
Este tema es mas que interesante... pero la cuestion es que es necesario ó que tipo de Antena se necesita para realizar un rebote a tanta distancia ??
Zero13

"Así como el hierro se oxida por falta de uso, también la inactividad destruye el intelecto.." - Leonardo Da Vinci

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#10
me encanta que pregunteis, esto es un mundo apasionante, es muy facil comunicar con la iss o con cualquier otro satelite, los hay que tienen bajada en 2.4 Ghz tambien, con un simple walki talki se puede comunicar con cualquier pais o hablar con la estacion internacional espacial, sin ningun problema.

Normalmente no son geostacionarios, os recomiendo, para empezar, usar el programa orbitron que es gratuito y os recomiendo visitar la web de mi amigo Pedro, donde hay videos y seguro que vais a alucinar, en esta web encontrareis info de como configurar el programa y muchas otras cuestiones, si alguien despues le surge alguna duda me tiene a su disposicion.

La web es: http://www.eb4dka.tk/
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#11
Entonces podriamos realizar un enlace de datos a 2.4 ghz entre dos puntos muy alejados ??... por ejemplo 300 kilometros ??, en teoria ambos deberian estar en las mismas condiciones... no?

Altura
Tipo de Antena
Hardware en General
Amplificacion Emision/Recepcion
Etc.
Zero13

"Así como el hierro se oxida por falta de uso, también la inactividad destruye el intelecto.." - Leonardo Da Vinci

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#12
yo pienso que si se puede hacer el contacto y espero intentarlo y conseguirlo este verano.

Ahora bien de conseguirlo no va a ser un contacto estable, eso por supuesto, probaremos las orejas de las zcom 325+ !!!

Habia que pensar en un protocolo de comunicacion para estas pruebas !!!

y a nivel de coaxiales, antenas y etc hay que usar algo curioso, al poder ser mas de 14 dbi´s y por ejemplo concretar previamente algunas cuestiones esenciales, como puede ser el tipo de polarizacion, ubicaciones exactas, etc, etc

Espero no parecer demasiado optimista, piensa que mi ventaja es por que esto ya lo he probado a frecuencias algo mas bajas, lo que pasa es que usando equipos mas sofisticados: previos de recepcion, etc.

Si no se intenta, seguro que no se consigue !!!
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#13
Estoy de acuerdo contigo... Wink
Zero13

"Así como el hierro se oxida por falta de uso, también la inactividad destruye el intelecto.." - Leonardo Da Vinci

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#14
Zero13 escribió:Entonces podriamos realizar un enlace de datos a 2.4 ghz entre dos puntos muy alejados ??... por ejemplo 300 kilometros ??, en teoria ambos deberian estar en las mismas condiciones... no?

Altura
Tipo de Antena
Hardware en General
Amplificacion Emision/Recepcion
Etc.

amigos si es posible.... revisen esto!!!!

http://www.neoteo.com/tabid/54/ID/3729/Default.aspx

:adios:
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#15
jeanmarquez escribió:amigos si es posible.... revisen esto!!!!

http://www.neoteo.com/tabid/54/ID/3729/Default.aspx

:adios:

382 km, waaaah, y con un ancho de banda de 3 Mbp/s!!, Es increible, y encima usando un router linksys de 40e... Muy Buena noticia, gracias!.
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#16
y yo que sonaba despierto dias atras pensando en wifi por rebote lunar... :meparto2:

yo pienso que tal desafio presenta varios contratiempos no limitantes, de hacerlo a una frecuencia de 10 mhz (no recuerdo a quien esta designado) la logitud de la onda tan solo mide 30 mts, hacer un dipolo de 1/4 de onda mide 7,5 mts cada elemento, para disminuir su tamano tendriamos que emplear una suerte de bobinas que no estoy seguro que tanto pudieran afectar el rendimiento de nuestra antena, asi que no seria tan cotidiano como ver un router wifi sobre la computadora de casa. Por otra parte, cuanta potencia emplear?, que hay de los protocolos, conexiones, etc?

No lo veo imposible, pero hay mucha tela que cortar mientras sea experimental; aplaudo la iniciativa de quienes quieran probarla. Animo!!!:plasplas:
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#17
sigo pensando que la DISTANCIA REAL a cubrir es demasiado alta (especialmente con el tema del rebote lunar) con los equipos que pueda tener alguien 'aficionado'...

origen de datos:
http://www.sc.ehu.es/sbweb/fisica/celeste/luna/luna.htm
http://es.wikipedia.org/wiki/Luna
http://es.wikipedia.org/wiki/Tierra

en el caso del rebote lunar: la DISTANCIA REAL seria: (Distancia del centro de la tierra al centro de la luna) 384.400 km - (Radio promedio de la luna) 1738 km - (Radio promedio de la tierra) [Radio ecuatorial (a): 6378 km Radio polar (b): 6357 km] {((a) + (b)) /2} 6367,5 km

esto son: 376294.5

(Fórmula de Friis) Lp(dB)= 92,45 + 20log10 F+20 LOG10d :
Lp= Path loss
F= frecuencia en GHz
dB= decibelios
d= Distancia en kilometros

Web que automatiza la formula:
http://www.radioptica.com/Radio/calculo_...nlaces.asp

Segun esa pagina serian 212 dB las pardidas, yo creo que serian mas pues la luna no es un material 'conductor perfecto' ni un reluciente espejo para las ondas de wifi :-P

Siendo 'generoso' con los nomeros...

Tomando una sensibilidad de recepción de -94dBm@1Mbps Gtx=Grx= 30dBd y estando conectados estos antenones a los AP por un pigtail que tiene una perdida total de -1dB (perdida del cable, de los conectores, de acoplo de impedancias) y dando un margen de funcionamiento de solo 1dB (escaso a mi gusto)


212-94+1-30+1-30 +1 = Ptx,necesaria

Ptx,necesaria = 61 dBm = 1258925mW = 1259 W


ED: rehago los calculos en cuanto encuentre el dato q falta :mrgreen: Big Grin
ED y PD: ahora si :-)
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#18
Muy pronto vamos a hacer pruebas en dos puntos alejados a 25 Kms. con antenas panel y cn antenas de DTV modificadas.
Veremos que resulta.
No soy experto en la materia, pro alguito se.
Lo que pueda lograr se los comunicara a Ustedes
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#19
Genial!.. estaremos atentos.
Wink
Zero13

"Así como el hierro se oxida por falta de uso, también la inactividad destruye el intelecto.." - Leonardo Da Vinci

Síguenos en TwitterYoutube

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#20
Amigo Zero 13
He aqui parte de los equipos que vamos a utilizar en las pruebas
Te agradeceria si pudieras decirme donde conseguir algon software como para medir la intensidad de la señal, ajustar el direccionamiento de las
parabólicas y todo aquello que creas conveniente y que este a tu alcance que pueda servirme.

[Imagen: equipo2lo1.jpg]

[Imagen: torre2bc5.jpg]

[Imagen: parabolicas2wt0.jpg]

[Imagen: directv03si0.jpg]

Vivo en un pueblo muy pequeño y me gustaria ser miembro VIP, pero lo unico que se consigue por aqui es Western Union y me muero por entrar a los sitios VIP a darme gusto. jejejejeje


Bueno ya la prueba preliminar la hicimos y colocamos algunas imagenes de lo que se hizo en esta localidad, entre 2 puntos a 15 Kms de distancia entre ellos.

http://www.zero13wireless.net/foro/showt...#post36879
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