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Forum Index : Microcontroller and PC projects : lora with hc-12
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| viscomjim Guru  Joined: 08/01/2014 Location: United StatesPosts: 925 |
I have been playing with a couple of different lora modules and now would like to do some range testing in an "urban" setting, ie in the neighborhood with trees and houses and such. I was thinking about setting up a "base station" on the roof of my house. In an effort to not have to run cables my thought was to use a micromite with an HC-12 on the console and the lora unit on com1. This would be powered with a sla 12v battery which would be charged using a small 10w Solar Panel with a small solar charge controller. This would all (minus the solar panel) be put in a waterproof case (probably something like tupperware or something). The HC-12 would have the little coil antenna that comes with it and the lora unit would have an external antenna . The lora is using 915Mhz at 1 watt. The HC-12 on the console would allow me to work in my office and change code, run and stop the program etc. Is there any reason I should be concerned that the two radios on the same micromite could cause issues with each other? Is this "bad practice"? |
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| ryanm Senior Member  Joined: 25/09/2015 Location: AustraliaPosts: 203 |
Different frequencies so it shouldn't be a problem. |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Agreed. There is about 500MHz separation between the HC12's in the 433MHz band, and the LoRA module on 915MHz - plenty of space between them.  Smoke makes things work. When the smoke gets out, it stops! |
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| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
I appreciate the replies. Never worked with RF before, and probably never would have if it weren't for the micromite! Somewhat addictive... |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
Second harmonic gets the HC12 to 866 so might do a bit of de-sensing. It depends on how clean the RF is and how well filtered the LORA module is. It "should" be OK Jim VK7JH MMedit |
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| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
TassyJim, that is interesting and makes me wonder if I am approaching this correctly. I want to get a "real" feel for what the lora modules can do and I don't want to degradate the lora signal with the HC-12 on the console, but I need to get this as physically high as possible, but cabling the console is not possible from my roof to the office.... I guess I will just have to try it, but I also don't want to face the ladder more than I need to... scared of heights, etc. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Me not like heights either.  The HC12's are very clean. I had a thread with one on the spectrum analyser back a while ago, and I could not even measure the 2nd and 3rd harmonics, so I would think you would be fine. It would be a good idea to do a site test BEFORE mounting any ladders. You could just use a long bit of pipe and tape the modules to that for the purposes of testing. Insulated from the pipe, naturally.... Smoke makes things work. When the smoke gets out, it stops! |
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| ryanm Senior Member Joined: 25/09/2015 Location: AustraliaPosts: 203 |
I've done a bit of work with LoRa modules. If you've got some details or even co-ordinates I might be able to give you an idea of what to expect. Be warned that those big range links you see are operating at extremely low data rates. My own networks generally operate at an effective rate of around 8Bps for the payload. |
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| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
Hi ryanm, thanks for the input. I am still in the infant stage of using these modules but can use any help I can get. Once I have the 1 watt modules set up between 2 micromites I will post my results. I did plan on using a low data rate for range testing, but did not consider using such a low data rate (8bps). I was basically going to set up my base station as in the first post and then make a "mobile" unit with gps and start roaming while logging position and hopefully transposing on google maps, etc. Have you used the E32 type modules? I quickly tried the reyax modules and was pleasantly surprised with the range using just the little on board antennas. These are 100mW so I can only imagine the 1w units will do pretty well, especially with a better antenna setup. If you don't mind, would you consider sharing some of what you have been doing with lora and what your typical setup has been? |
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| HankR Senior Member Joined: 02/01/2015 Location: United StatesPosts: 209 |
Jim, At maximum power the datasheet claims +15 dBm, so that's only 32 milliwatts. There's mention of a filter's loss (of a max of 3 dB) and it's not explained whether that's after or before the +15 measurement. Knowing the way spec sheets are very craftily written, I'll bet it's after, so that means the max. output power to the lossy twisty antenna could be as low as 16 milliwatts, and no higher than 25 milliwatts. More in a later post about the real output of your other LORA unit (it's also less than you think), and the limitations of the legal use of these units in the US. Hank |
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| HankR Senior Member Joined: 02/01/2015 Location: United StatesPosts: 209 |
I think I know what you mean by effective data rate, but to avoid confusion on this subject, what is the approx. raw data rate you use without accounting for various types of overhead? In bps or baud. Hank |
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| HankR Senior Member Joined: 02/01/2015 Location: United StatesPosts: 209 |
Under the terms of the US FCC type acceptance, that antenna would definitely be illegal. In the test report submitted as part of the US type acceptance process, there is only one antenna that is permitted, a little stubby rubber antenna. There is a clause in the applicable part of FCC Part 15 that probably does not apply to this device the way the type acceptance was applied for, but if this clause were invoked, a higher gain antenna would only be allowed if the transmit power were lowered to exactly cancel out the added gain of the bigger antenna you have in mind. There can be good reasons why one would do this even though the range would be unaltered compared to that attained by the little rubber one. The 1 watt power might be okay in the US; I'm not sure yet. The permitted levels are based on the specific modulation used by the device and are either .25 watt or 1 watt. 1 watt probably okay. I only mention all this to show that type acceptance terms must be followed in the US no matter what is legally permitted in other areas of the world. I have read somewhere that German emission standards are very generally speaking more stringent than the US, and the Japanese standards are the toughest of all. Most US standards are based on radiated field strength and don't even mention power level. FS is measured in unit emf/unit length, so that is typically in microvolts/meter. Hank EDIT: I keep hitting by mistake post instead of preview |
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| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
Hi Hank, before I purchased these modules, I found some info about the FCC limitations... FCC Rules for Unlicensed Wireless Equipment operating in the ISM bands The ISM radio bands were originally set aside for electromagnetic radiation produced by industrial, scientific and medical (ISM) equipment. In the early 1990's the Federal Communcations Commission (FCC) allowed using three of the ISM bands for unlicensed communication equipment. These three ISM bands are: 902 to 928 MHz <<< Thess modules are 915Mhz 2.400 to 2.4835 GHz 5.725 to 5.875 GHz In the United States the use of these bands for communication purposes is regulated by part 15 of the FCC rules. Maximum Transmit Output Power in the ISM bands Several of the FCC part 15 rules govern the transmit power permited in the ISM bands. Here is a summary of those rules: Maximum transmitter output power, fed into the antenna, is 30 dBm (1 watt). Maximum Effective Isotropic Radiated Power (EIRP) is 36 dBm (4 watt). You can obtain the EIRP by simply adding the transmit output power, in dBm, to the antenna gain in dBi (if there is loss in the cable feeding the antenna you may subtract that loss). The modules also have an FCC label on them, but you know how that goes sometimes with products from China. I was hoping that these modules would fit in the above guidelines for the US. Based on very little knowledge I am assuming that the module (30dbm) plus the antenna gain (3.5dbm) 33.5dbm is within the limitations. Plus I am assuming there is a bit of loss in the cable. Does this seem correct to you? |
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| srnet Senior Member Joined: 08/08/2014 Location: United KingdomPosts: 164 |
Why you would need as much as 36dBm from a LoRa device I cannot imagine. Estimated LOS range at a LoRa Bandwidth of 125khz and spreading factor of 12 (300bps) would be in the 7,000km range. With a small yagi you could get as far as geo-stationary satellite height. $50SAT is Silent but probably still working. For information on LoRa visit http://www.loratracker.uk/ |
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| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
The original plan was to just get an idea of how well these could do in an "urban" environment in my neighborhood with trees and houses that may not have an ideal LOS. But the future plan was to have the base station at a boat dock, high on a pole, and have a couple of remote units with GPS and a couple of other sensors installed on sponging boats that are prevalent in my home town. I have a few friends that do this for a living, so getting them on the boat is not an issue. These guys go out a few miles to do their jobs and these could possibly make for really neat trackers for the boat owners, where cell coverage may not work too well out in the gulf of mexico. This way they are not relying on coordinates radioed in by the captains, or using a cell based gps tracker that may not work out there, and they can track the location of their boats and some sensor readings at any given time. Plus, no license needed or monthly costs for cell service, and bonus, I get to play with what I love. The listing for the lora module shows a distance of 8000 meters, but you indicate a LOS range of 7000km at 300 bps. This is quite impressive, I must say. I will keep my data rate relatively slow to get the distance, but based on what you said, I might be quite surprised at the results. I know I probably have to take the curvature in to account, but again, still learning and this is a cheap way for me to experiment. |
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| Paul_L Guru Joined: 03/03/2016 Location: United StatesPosts: 769 |
You're dealing with line of sight propagation. The theoretical geometric distance to the horizon can be derived from the Pythagorean theorem if you know the height of the antenna. It works out to D(mi) = 1.23 x H(ft)^0.5 or D(km) = 3.57 x H(m)^0.5 This equates to a range of 7.14 km for an antenna height of 4 metres. However, RF radiation bends as it passes through an atmosphere. (This is visible if you watch the fuzzy edges of the shadow of the earth on the moon during an eclipse.) So a fudge factor of 4/3 is usually applied for good weather conditions. D(mi) = 1.41 x H(ft)^0.5 or D(km) = 4.12 x H(m)^0.5 This equates to a range of 8.24 km for an antenna height of 4 metres. If the both the receive antenna and the transmit antenna are 4 metres high then the effective range would be doubled. (The circular limit of the transmit pattern would touch the circular limit of the receive antenna tangentially.) When it starts raining all bets are OFF! Paul. |
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| ryanm Senior Member Joined: 25/09/2015 Location: AustraliaPosts: 203 |
I haven't used any Chinese units. I use ones from an Australian company called Modtronix. Getting good reception at very low data rates is based off the precision of the crystal and I just don't trust Chinese stuff when there's Aus stuff for $20 per unit. Max transmit power on a SX1726 without duty cycle restrictions is 17dBm. That power should easily get you up against LOS boundaries on the ocean, antenna height will be your key to range.. The Chinese ones with higher TX powers must throw that output through another amplifier, which depending on the quality might actually introduce more noise than the extra power is worth. One absolute golden rule for loRa radios (assuming module to module not LoRaWAN) is to use all the same model in your network. Manufacturing tolerances and circuit design mean that different manufacturers have slightly offset frequencies from each other. Also they will have their own frequency shift with temp, but if all the radios are shifted by the same amount on a hot or cold day it won't affect your signal. Data rate I quoted was 8Bps <= note the capital. That example is based on a 12 byte packet taking 1450ms to transmit, 400ms of which is the LoRa pre-amble so 12 / 1.45 = 8.3 bytes per second for the packet including overhead. For the actual symbols transmitting useful information you are looking at (12 x 8 ) / 1.05 ~ 92bps or baud for the payload. |
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| srnet Senior Member Joined: 08/08/2014 Location: United KingdomPosts: 164 |
702km LOS (ground to high altitude balloon has been achieved at 868Mhz and 14dBm. An output of 34dBm, would be 20dBm more, which is 10 times distance. Of course the Earth is bendy and you would need the comms to be to\from a satellite to test this. $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 |
Thats not necessary in my experience. Just choose a suitable bandwith and there is plenty of leeway to allow inter communication between different manufacturers devices. I dont recall a problem mixing manufacturers devices when used at a bandwidth of 62.5khz in 4 years of regular use of LoRa. And yes I have tested with modules in deep freezes and\or ovens. In measurements I recall doing in the early days, typical maximum frequency shift between device was +\- 4khz @ 434Mhz, and a specific manufacturers devices could be + or - offset. $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 |
Not necessary at all, LoRa is a standard and different gear works really well together, but if you're chasing that last little bit of signal 15kms apart it helps to have all the modules the same. |
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