LowPowerLab Forum

Hardware support => RF - Range - Antennas - RFM69 library => Topic started by: KrisK on November 13, 2016, 09:55:21 PM

Title: Basic Battery Life Questions 433 vs 868 vs 915Mhz
Post by: KrisK on November 13, 2016, 09:55:21 PM
I have been reading a bunch.   And I truly want to thank every advisor that gives such qualified advise freely.   This has helped me beyond explanation (I can only hope to post worthy advice in the future)  More kudos goes first and foremost to Felix for developing one heck of a product.   In just a short week from Order to Receipt I can now move forward with a product that is a (Hobby Business) to hopefully something more.    Kudos again to all.

Here is the question:   If the same code was running on the Moteino with the RFM69 how much longer would the battery last between these 3 frequencies and the W vs HW. 

I'm not an electronics guy just a old C programmer enjoying the heck out of this stuff.     My tests proved the RFM69HW had far more range than I ever thought outside.   Now I need to make sure the operators don't get frustrated by having to replace batteries every day.   I do plan on putting a solar panel to help recharge batteries and work on sleeping the devices periodically.   

Thanks again for any/all advice.


Title: Re: Basic Battery Life Questions 433 vs 868 vs 915Mhz
Post by: Felix on November 14, 2016, 08:37:00 AM
To my knowledge and observation so far the frequency does not make a difference. The actual data is just carried over the carrier frequency which can be either of the 3 bands (in fact the radio chip (http://www.semtech.com/images/datasheet/sx1231h.pdf) could output from an even larger range.
Where frequency makes a difference is obstacle penetration. The higher the frequency the lower penetration, it's just physics there. Also you have to mind the allowed ISM bands in your country/area etc.

The W and HW are 2 different implementations of the same RF chip which happens to have 2 RF output paths, which include a combination of PAs (power amplifiers) with different gains up to a total of 20dBm possible in the HW, and 13dBm in the W variant.
0dBm is 1mW, the reference point, each 3dB is a doubling in output power on the log scale (or halving when you go negative).
So from 13dBm to 20dBm there is 7dBm differece, that's a LOT in terms of power. There are ways to save power which are discussed in this forum. But it's all a tradeoff in terms of range and consumption etc. You can reach farther bu shouting louder. Or you can tweak your radio settings at lower bitrate and bandwidth. At extremely low bitrates folks have transmitted from lower atmosphere with a range up to 160-200km, using the RFM69HW (still highest output). That's just to illustrate what kind of range is achievable in line of sight conditions. But it gets complicated to keep the receiver and transmitter very tuned to the same very narrow frequency channel at those low bitrates.
The default settings in RFM69 lib give you an all around "best" set of out-of-box settings that will work in most conditions with the RFM69 radios without you having to worry too much at least in prototyping stages. When you need to get more specific or have more exotic requirements you can tweak the radios to your requirements, there's a lot of research already done and shared in this forum in that direction.
Hope this helps, and thanks for the compliments :)
And more contributions and input and corrections to my mistakes always welcome from others of course.
Title: Re: Basic Battery Life Questions 433 vs 868 vs 915Mhz
Post by: KrisK on November 14, 2016, 09:32:48 AM
Great information.   I sure thought the frequency mattered on power consumption.    I knew dB was big but I thought frequency was also. 

I can code for the battery life down the road and will make use of some of the forum suggestions.     The longest I really need through trees will be 300 yards.   So playing with the DB might be all I need.    I actually believe I can integrate a small solar array on the project box to recharge the batteries extending their life.     

Again thanks for the help.    Now the work actually begins.