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Forum Index : Microcontroller and PC projects : lora with hc-12
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| ryanm Senior Member  Joined: 25/09/2015 Location: AustraliaPosts: 203 |
Terrestrial that is. The range even on the ocean is going to be orders of magnitude less than a satellite with a clear fresnel zone. Definitely a bit strong on the wording re-reading that. |
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| srnet Senior Member Joined: 08/08/2014 Location: United KingdomPosts: 164 |
Never noticed a differance myself, and I have tested at much longer range than 15km. Different modules all use the same LoRa chip, SX127x, so same firmware too, the only difference between different manufacturers modules is the antenna matching components and crystal. As long as the frequencies are fairly close, and that is an issue between modules form the same manufacture as well, I dont see how sticking to one manufacturer improves range. There is some link testing software here, that could be use to test; https://github.com/LoRaTracker/Link-Tester2 With suitably attenuated transmitters the testing could be over a local park. $50SAT is Silent but probably still working. For information on LoRa visit http://www.loratracker.uk/ |
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| srnet Senior Member Joined: 08/08/2014 Location: United KingdomPosts: 164 |
If you want to squeeze the last bit of range out of a LoRa module, then do tune the antennas to suit each module. The required tuning does vary between modules, so the optimum length\tuning for one module might not be the same as for another. There some tests and graphs of the variances between modules and how to carry out simple antenna tuning here; https://github.com/LoRaTracker/AntennaTesting You can get improvements of between 1dBm to 2dBm by matching antennas to modules. $50SAT is Silent but probably still working. For information on LoRa visit http://www.loratracker.uk/ |
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| ryanm Senior Member Joined: 25/09/2015 Location: AustraliaPosts: 203 |
Curious to know what sort of range the boats go out to from the dock viscomjim? Did I read your post and then google wrong or are they diving for sea sponges? They must be worth a bit to send out a boat. |
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| viscomjim Guru  Joined: 08/01/2014 Location: United StatesPosts: 925 |
Tarpon Springs is "the sponge capital of the world" and there are quite a few boats here at the dock. I will have the distances they go out later today. The sharing of GPS coordinates for where they ply their trade are not handed out very freely, as you can imagine, but they know I'm not going out to "sponge" their sponges. The gps coordinates will let me check LOS distances from the dock where I plan to place the base antenna using google earth pro to see if this is even feasible. I found a couple of nice antennas for 915mhz at digikey.   |
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| HankR Senior Member Joined: 02/01/2015 Location: United StatesPosts: 209 |
For quite a complete history of sponge diving going back 170 years in history (mention is even made to the time of Aristotle), see the "Story of Sponge Divers." It will tell you a lot about the modern capital of sponge diving, Jim's Tarpon Springs, Florida. story of sponge divers |
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| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
Well, I spoke with a couple of captains and they would like to see 30 miles or so out of something like this, and using the formula from Paul L. (D(mi) = 1.41 x H(ft)^0.5), both the boat and the base antenna would have to be at about 120 feet in the air to achieve the LOS for this distance. I can see how the ground station to satellite would work well in this situation, but with the roundness of the earth in the equation, 30 miles would probably be a bit difficult to achieve over water. This antenna has a gain of 5dbi, so could work well. Once built, I still want to see how far out on the water this will go with the remote having a gps unit so I can measure distance. I should be able to get a bit of height on the boat and the base uint, but the 30 mile thing might be out of the question due to antenna height... |
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palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1993 |
From what I have seen on the internet PaulL.'s formula is a bit out. Have a look here.Distance to Horizon From that you need an antenna 600ft. high. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| HankR Senior Member Joined: 02/01/2015 Location: United StatesPosts: 209 |
There is nothing wrong with PaulL's formula or Jim's arithmetic. Paul's entire post's content can be found in Wikipedia and that info in Wikipedia I've confirmed to be correct. Paulpc (palcal), first of all, your calculator determines what I call optical line of sight or geometrical line of sight. Jim is properly using the 1.41 factor which is an approximation for the behavior of radio waves, which in certain wide frequency ranges (including VHF), travel a little further than the optical range. Second, Paulpc's figure of 600 feet for a single elevated antenna is correct (for optical), but Jim's gave the instance of two equally elevated antennas. Using the LOS calc for one antenna and 15 mile range now yields 149 feet. Correcting that 149 feet for the approximation for radio behavior gives the originally stated and correct 120 feet for two elevated antennas. to achieve a combined 30 mile range for the path. |
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| HankR Senior Member Joined: 02/01/2015 Location: United StatesPosts: 209 |
See this calculator which very handily accepts two antenna heights and yields two separate radio horizon distances. Radio horizon calculator for two antenna heights |
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| HankR Senior Member Joined: 02/01/2015 Location: United StatesPosts: 209 |
Adequate radio line of sight is a necessary but not a sufficient condition for received signal to noise ratio to be high enough for a successful link. Lifted from the internet: A necessary condition is a condition that must be present for an event to occur. A sufficient condition is a condition or set of conditions that will produce the event. A necessary condition must be there, but it alone does not provide sufficient cause for the occurrence of the event. With radio we have now left the relatively uncomplicated digital world and have entered into the wider physical world where answers and situations are very often not defined by simple black and white, yes or no states. This makes it a little harder to give full and adequate answers in this format favoring quick, short, hit-and-run type posts characteristic of internet forums and mailing lists. |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
Optical horizon: Formula assumes the earth is round which is not quite true. Formula cam from palcal's website link. end the input with 'f' for feet, otherwise metres. Radio gives greater range due to bending. From my location at 240M and view of the sea Observer's Height? ? 240 55.3 Kilometres. 34.4 Miles. 29.9 Nautical Miles. Observer's Height? ? 40000f 394.6 Kilometres. 245.2 Miles. 213.0 Nautical Miles. Observer's Height? ? To get the distance between two observers. add them together. I receive aircraft on 1.09GHz out to 300NM on a regular basis. Ships on 162MHz go from ~35MN to 300NM+ when there is an inversion. Jim VK7JH MMedit |
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| Paul_L Guru Joined: 03/03/2016 Location: United StatesPosts: 769 |
@Jim -- That's about the way it works. When I was with Pan Am we would get a usable VOR signal on 115.4 MHz about 365 miles from Gander NL on a great circle route from LHR to JFK. The Gander DME in the 340 MHz band would lock on at about 325 miles. HF comms on 5.345 MHz would bend in troposcatter so the ground wave would reach all the way across the pond reliably. HF comms in the 3 MHz band would reflect off the Kennelly-Heaviside E layer depending on sunspot activity. I could sit on the ground at JFK in the middle of the night and work the 20 metre ham band with my K2JLN call sign, using one of the Collins 618T2 transmitters in a 727 and get QSL cards from Hong Kong. RF propagation is a very peculiar thing. Paul in NY |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
@Paul I used to work 160 metres. That had interesting propagation when the grey-line was working for us. Much more fun than these itty-bitty frequencies. Jim VK7JH MMedit |
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| HankR Senior Member Joined: 02/01/2015 Location: United StatesPosts: 209 |
The code from the website Palcal linked to is the worst I've ever seen. I'm talking about things like the ridiculous constant of 4.06 x 10^13 among other absurdities Hilarious. ROTFL. Instead of the inaccurate rounded-off figure of 40680631590769 the web programmer used, why not use the best true value available now of 40680631590769.1828459045235 measured by the US National Institute of Standards and Technology? False precision - Wikipedia "False precision (also called overprecision, fake precision, misplaced precision and spurious precision) occurs when numerical data are presented in a manner that implies better precision than is justified; since precision is a limit to accuracy, this often leads to overconfidence in the accuracy, named precision bias." False Precision |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
Many of the MMBasic device do use double precision. 40680631590769 is within the range of double precision floating point. As long as you are aware that the distance is for optical horizon it is not that "hilarious" Jim VK7JH MMedit |
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| HankR Senior Member Joined: 02/01/2015 Location: United StatesPosts: 209 |
Jim, This has nothing to do directly with the precision available to some of the MM devices. I have no issue whatsoever with your very nicely done translation to BASIC. It is about the self-described mission of the website calculator and the code used to achieve that. The following is a statement verbatim from the website itself: "This is a rough guide to determine the distance of the horizon based on the observer's height above mean sea level." So the constant referred to before, needing an exponent of 10 to the thirteenth power when expressed in scientific notation -- that's pretty absurd from the point of view of the principle of false precision explained in the prior post. Even though it appears in an intermediate calculation, 14 digits in all is just kind of silly. I hope everyone not already really familiar with what false precision is (also by other names such as "fake precision" which I like) might read the wikipedia entry. I'm sure there are plenty of other internet sources on precision to be found. It's of course included in any college introductory but rigorous text (i.e., meant for science or engineering majors) on physics or chemistry, and many engineering texts as well. Here's one of the funny illustrations of FP from Wikipedia: "False precision is the gist of numerous variations of a joke which can be summarized as follows: A tour guide at a museum says a dinosaur skeleton is 100,000,005 years old, because an expert told him that it was 100 million years old when he started working there 5 years ago." Hank |
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