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I'm very new to radio communication so I apologize for the lack of knowledge about this subject.

That being said, I'm looking for a directional antenna imagine a situation as follows, I'm in a rural area where the nearest cell tower would be 20-25 miles away my phone is completely in the dark and is unable to communicate with the tower.

So I need an antenna, there are no other cell towers around and due to the higher gain we're going for a directional one in this case.

I'm considering a high gain antenna either a Yagi-uda or a Parabolic antenna since those are high gain and with a high dBi I think I'll be able to reach the tower.

I need to communicate both uplink and downlink, with an average speed of 1-3 MB/s, the cell tower communicates using 1800MHz as the frequency.

Ideally I would use an antenna which would be portable, which something like a Parabolic antenna isn't, neither is the Yagi-uda, however I realize that this might not be possible.

I know that the transmitting power, line of sight, dBi, frequency and a lot of other factors are in play, how do we determine if our antenna would be able to reach, estimating a clear line of sight?

Thank you in advance!

icyli2
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  • Nothing trivial in this case. The clear sight line over the horizon is not enough. There must be also enough free space around the sight line.. Radio communication engineers call the needed free space "Fresnel zone".. See these links for the tower height calculations https://en.wikipedia.org/wiki/Horizon and https://en.wikipedia.org/wiki/Fresnel_zone The needed Fresnel zone can easily double the needed tower height. A legal thing: You may live in a country where one has no right to use amplifiers nor high directivity antennas for transmitting. –  Jan 17 '22 at 08:55
  • (continued) Why? There can be a limitation of the allowed transmitting power and it can be given as the maximum allowed power density at certain distance., not as watts, but as watts/square meter. Or equivalently as decibels over one milliwatt with non-directing antenna. Finally the operator can use communication signalling that doesn't allow so much signal flight delay as you need. –  Jan 17 '22 at 09:00
  • This location is based in Europe so it falls under the ECC (among others) standards. I'm not to sure about the max transmitting power but from previous research the max dBi should be 30. In regards to the Fresnel zone, it's in the center of a forest, double the tower height seems well very high but possibly I'd be able to put it in a very high tree or put up a pole on the roof and attach the antenna to it. Is there any hope of being able to achieve a connection? – icyli2 Jan 17 '22 at 18:59
  • Have you already calculated how high antenna tower you need for clean over the horizon and obstacles sight when you know the distance,, how high obstacles there are on the route and how high is the phone company antenna tower, the elevation (from sea) of your place and of the phone company tower? Add to that the radius of the 1st Fresnel zone at 1800MHz frequency and 25 miles distance. –  Jan 17 '22 at 19:44
  • I haven't but it sure seems like a lot of steps to take, how would this correlate with determining if this antenna would be able to reach? I'm not sure about how high the carriers tower is nor the sea level of the place but in regards to the Fresnel zone, if I put the antenna on a large tree or a pole on my roof I'd be able to get about 30-40 meters above all obstacles (since the surrounding area is mainly filled with tree's). I think I'll be able to pass most obstacles there are if not all it's quite a deserted area after all. – icyli2 Jan 18 '22 at 02:47
  • Assuming a near perfect environment, 40 meters above the trees is there a rough estimate as to how much dBi and transmitting power I'll need? Or maybe a formula which estimates what range an antenna will have? It's hard to get these values practically (how high the tower is) and this is my vacation house, I've been researching for weeks but would love to find a simple method to determine whether I'll be able to reach. If there's no other way I'll get these values and report back. – icyli2 Jan 18 '22 at 03:20
  • 40 meters tower as a minimum will cost some real money. Have you asked from the phone operator "how high tower and what antenna & phone gear I need?" Their engineers (or their engineering subcontractors) have on geographic data based tools to calculate it in seconds. It's different thing do they bother to answer. Drawing manually the terrain profile is possible, too, but it's a hard job. A drone owner may be able to help you to do some practical tests. I guess you should search for satellite phone operators and satellite internet providers. About power: see Friis transmission equation. –  Jan 18 '22 at 07:15
  • Thanks for the detailed explanation, using a drone (if I can find one who communicates on the same frequency range) seems like a good and easy method! – icyli2 Jan 19 '22 at 01:45
  • @user287001 After some research I found out about the "free space path loss" formula which calculates the maximum theoretical range of an antenna under perfect conditions. Do you think it's possible to use this formula to get a rough estimate range of how much range an antenna will have under less ideal conditions? Everyone keeps referring me to the environment an although I understand it's a crucial factor to equate the range, what if we'd plan to use the antenna in multiple different areas, or these values are unable to be determined? – icyli2 Jan 28 '22 at 14:07
  • By the way, what about RF amplifiers? From my understanding (which is limited) these should work similar to audio amplifiers I.E they make the received signals "clearer" maybe this is something which can be added to get the maximum range possible? I would love to just look at an antennas technical specification and just pinpoint a rough range that it'll have but it seems that it's way more complex than this, and even engineers need to look at all these factors to determine an accurate range? – icyli2 Jan 28 '22 at 14:11
  • Free space path loss formula is the Friis Transmission Equation. If you know the max distance for proper connection in surely free space you can calculate how much more you get by increasing the receiver antenna gain, the transmitter antenna gain and transmitter power. The formula knows nothing of your environment. You must know how much extra loss your environment causes. Amplifiers in receivers are useless, they amplify the noise, too, assuming you cannot afford cryogenic space- or medical imaging technology devices. –  Jan 28 '22 at 15:08
  • @user287001 You're right, factoring in the environment will be the only way to get an actual accurate measure, I've tried the FSPL formula already but it's giving me absolutely insane ranges (150km on 2.4GHz with a 16dBi Yagi-Uda). Is there a formula so that we can calculate this ourselves or would it require help from the cellular operator? – icyli2 Jan 29 '22 at 08:29
  • Check this: https://www.researchgate.net/profile/Oskar-Wibling-2/publication/2643036_Terrain_Analysis_with_Radio_Link_Calculations_for_a_Map_Presentation_Program/links/56731e2408ae04d9b099c223/Terrain-Analysis-with-Radio-Link-Calculations-for-a-Map-Presentation-Program.pdf It's a cross-section of terrain analysis of radio link engineering. It presents also a developed new tool. Search for more info sources. I'm afraid you cannot invest to get the data and knowledge needed to do your calculations by yourself. Ask at first the cellular operator which antenna, tower and equipment you need. –  Jan 29 '22 at 08:50
  • Thank you very much for your help, I'll have a go at it soon hope I'll be able to get a signal! :) – icyli2 Jan 29 '22 at 09:28

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