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Topic: E32-TTL-100 - How to use the RF module? (Read 4698 times) previous topic - next topic

Robin2

I seem to be getting extremely low bandwidth (with uart at 115200 and rf at 19200) when trying to receive a stream of gnss data, distance not being the problem. Do I miss something basic like having to change default channels?
What is missing is a complete description of the hardware you are using and the code for the programs you are using.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

epigramx

#16
Mar 23, 2019, 02:02 pm Last Edit: Mar 23, 2019, 02:35 pm by epigramx
What is missing is a complete description of the hardware you are using and the code for the programs you are using.

...R
Nevermind, my main problem was a misunderstanding of what those modules can do. The first practical problem I noticed is that it's relatively nonsensical to use a different UART rate compared to air rate unless you can guarantee you won't go above the air rate since the module appears to be implied by the manual-datasheet that has only 512bytes of cache (so it's a dropped-data galore that way [if you try to stream something like a big file] when it's already easy to drop data if you meet the air rate anyway).

Secondly, generally the modules are VERY low bandwidth by design so one should be careful to not try to send anything too populous [and above the air rate] (like the GNSS data I try to send; I can but I have to reduce them first). Something crucial is that they also have an error correction mode on by default (FEC) which is an EXTREME bandwidth hog so one should only enable it if they are absolutely sure they can get away with the lost bandwidth.

srnet

#17
Mar 23, 2019, 03:31 pm Last Edit: Mar 23, 2019, 08:20 pm by srnet
Something crucial is that they also have an error correction mode on by default (FEC) which is an EXTREME bandwidth hog so one should only enable it if they are absolutely sure they can get away with the lost bandwidth.
The use of FEC is implicit in the use of LoRa, you cannot turn it off all together. Ebyte have an option for turning it on and off, I suspect that might actually just be changing the rate from 4:5 to 4:8.


You can (with the native LoRa device) set the rate from 4:5 to 4:8.

The standard FEC rate, 4:5 adds 25% to the number of bits sent, hardly an 'EXTREME bandwidth hog'.
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srnet

#18
Mar 23, 2019, 03:39 pm Last Edit: Mar 23, 2019, 08:21 pm by srnet
Secondly, generally the modules are VERY low bandwidth by design so one should be careful to not try to send anything too populous
In LoRa technology bandwidth is used to refer to the RF bandwidth of the LoRa signal, which can be set between 7.8Khz and 500Khz. Bandwiths of 62.5Khz and lower give longer range but really require the modules to use temperature compensated oscillators, so mostly not used due to cost considerations.

A (high) bandwidth of 125Khz is most used in IOT applications.

The UHF LoRa devices were not designed to stream large amounts of data, rather to provide extreme long range links for low data rates in a very battery efficient manner.
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epigramx

#19
Mar 24, 2019, 08:47 am Last Edit: Mar 24, 2019, 08:54 am by epigramx
The use of FEC is implicit in the use of LoRa, you cannot turn it off all together. Ebyte have an option for turning it on and off, I suspect that might actually just be changing the rate from 4:5 to 4:8.


You can (with the native LoRa device) set the rate from 4:5 to 4:8.

The standard FEC rate, 4:5 adds 25% to the number of bits sent, hardly an 'EXTREME bandwidth hog'.
I do not know if they practically violate the standard on their config tool. I talked of their config tool specifically ("RF_Setting") which only shows "FEC ON", "FEC OFF" and when it's enabled it's extremely higher bandwidth compared to being off when bandwidth matters (e.g. when you need to squeeze your data - comfortably - in 9600 and when it's on, only 19200  may do it) [the word "extremely" is subjective anyway, so let's not delve too much into that, in the example I gave it can be considered an important overhead in any case].

[PS. Their manual/datasheet also only includes phrases like "After turn off FEC"]

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