Long Distance Microwave Transmission Experiment

Long range WIFI is becoming ever more popular with a growing demand for faster and more stable connections worldwide. In rural areas where cable broadband is not available, the deployment of microwave antennas is a low cost and reliable alternative to reach those remote areas. Deployments of permanent, stable, high speed links reaching distances greater than 100km are often accomplished, and in extreme cases, distances in excess of 300km have been realised.

Long range WIFI is becoming ever more popular with a growing demand for faster and more stable connections worldwide. In rural areas where cable broadband is not available, the deployment of microwave antennas is a low cost and reliable alternative to reach those remote areas. Deployments of permanent, stable, high speed links reaching distances greater than 100km are often accomplished, and in extreme cases, distances in excess of 300km have been realised.

Following the recent laser experiments across Lake Balaton and Lake Ijssel, FECORE plan to conduct a new experiment using the latest in microwave technology to further test for any evidence of curvature over large bodies of water. This experiment will take place from the coast of England across the North Sea to the coast of Holland at a distance of 148km.

What sets our experiment apart from the rest, is the proximity of the antennas to the water. With a proposed height of approximately 60m on one side and 37m on the other, the radius of the Fresnel Zone is an important consideration, especially given that a reflective surface, such as water can cause severe interference to a microwave transmission. The rule of thumb is that the 1st or the Primary Fresnel Zone would ideally be 80% clear of obstacles, but must be at least 60% clear.

In selecting the best frequency to use for our experiment, simulations were conducted using the antenna manufacturers online simulation tool. The images below show that the Fresnel Zones of frequencies less than 5GHz will not clear the surface of the water. Also of note is the height of earth’s curvature as simulated using their online tool.

With the proposed antenna heights, our calculations show this to be a clearance of 4.5 meters from the surface of the water to the bottom of the 1st Fresnel Zone. Of course at high tide, this clearance could reduce by as much as 2.5 meters however this still leaves the zone 100% clear for our experiment.

It is well documented that weather and other atmospheric conditions have an affect on microwave transmissions, resulting in the microwave beam refracting up or down. In permanent deployments however, the customer expectation is to communicate over the link any day, any time, and it needs to perform consistently, not influenced by the weather or any other environmental condition. These expectations impose some practical limitations, line of sight being one of them. It is for this reason that microwave antennas are often installed on high mountain tops when transmitting over land.

A variable known as ‘K-Factor‘ is sometimes used when determining if two sites are suitable for a deployment. The K-factor is used to change the effective radius of the earth, typically to 1.33 times its accepted size. This is due to the atmospheric refraction of microwaves causing them to either bend downwards (typical k-factor = 4/3) or to bend the signal upwards away from the earth (k-factor less than 1). It is suggested to use a k-factor of 4/3, 1, 3/4 and 1/2 when performing any link analysis, as when the k-factor changes on a day to day basis due to the weather, the link should always remain operational.

It is worth noting that in the case of our experiment, by applying the typical k-factor of 4/3 (1.33) to the radius of the earth, the antennas on both sides would need to be a minimum of 366 meters above sea level to refract down over the curve and attain a successful link.

Using AutoCAD, it is possible to determine exact radius that the earth would need to be in order for the link to be line of sight, and for the 1st Fresnel Zone to clear the surface of the water. In the case of our experiment, the earth’s radius would need to be 602,847 km, or 94.62 times its accepted size.

The image below is taken from a simulation made using the Radio Mobile online calculator. Just as with the antenna manufacturers online tool, it too shows that there should be no possible link between the 2 sites for this experiment.

 

 

 

From these simulations it is clear that we must transmit on a frequency of 5GHz or higher to stand a chance of obtaining a link. Although an 11GHz system is capable of higher transmission rates, the drawback is, that the signals are more susceptible to bad weather and because we are not interested in achieving a high capacity transmission, we have opted for a 5Ghz system for this experiment.

The image below, taken from an online Fresnel Zone calculator shows that at a frequency of 5.725GHz, and a distance of 148km, the beam yields a 44 meter radius at the midpoint.

It is therefore apparent that all trusted sources that can predict and calculate the viability of a successful microwave link between two sites, show it to be impossible, simply due to earth’s curvature. Therefore if a successful link is established during the experiment, it will cast serious doubt over the existence of a curved earth. And using the typical K-Factor = 4/3 does not increase the radius of the earth nearly enough to allow for a link of this distance, at these elevations.

If and when a link is established, it will be monitored using real-time signal strength data obtained from the radio’s built-in software. The duration of monitoring will be enough to ensure that a stable connection is maintained throughout varying atmospheric and weather frontal systems. If it maintains a stable connection then it can be considered ‘permanent’ for the purposes of this experiment, bringing in to question whether or not the sea is curved or whether it is indeed flat.

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