Learning about 433 MHz radios - how?

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Re: Learning about 433 MHz radios - how?

Post by zoomx » Wed Mar 22, 2017 4:29 pm

Squonk42 wrote:It looks like RFM69s are just (legal?) repackaged SX1231H chips:
https://lowpowerlab.com/forum/rf-range- ... es-or-not/
Note: Although not documented, the Hope RFM96 actually supports Semtech's Low Data Rate Optimization (supported by Semtech SX1272 and SX1276) so we can use LoRa Mode 1 for maximum range, minimum bandwidth transmission. Refer to Page 28 of Semtech SX1272 Datasheet: http://www.semtech.com/images/datasheet/sx1272.pdf

Low Data Rate Optimization Given the potentially long duration of the packet at high spreading factors the option is given to improve the robustness of the transmission to variations in frequency over the duration of the packet transmission and reception. The bit LowDataRateOptimize increases the robustness of the LoRa link at these low effective data rates, its use is mandated with spreading factors of 11 and 12 at 125 kHz bandwidth.

Hope RFM96 seems to be derived from the Semtech SX1276: http://www.semtech.com/images/datasheet/sx1276.pdf. Although not documented, Hope RFM96 (but not RFM95) supports the Low Data Rate Optimization setting in RegModemConfig3 (register 0x26) exactly the same way as the SX1276. See Page 114 of the SX1276 datasheet. I confirmed this by checking the Hope library code (HoepRF_HSP_V1.0\libraries\HopeRFLib\HopeDuino_LoRa.cpp) at http://www.hoperf.com/demo_tools/419.html

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Re: Learning about 433 MHz radios - how?

Post by stevestrong » Wed Jun 28, 2017 2:44 pm

RogerClark wrote:
Thu Mar 16, 2017 9:06 pm
nRF905 is another option

but I had to hack an AVR library to use it, and the result was not pretty;-)
Hi Roger,
can you share the hacked nRF905 code (even if it is not pretty)? I am interested to test it, I have a project to control my home ventilation system which uses a protocol based on this chip.

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Re: Learning about 433 MHz radios - how?

Post by RogerClark » Wed Jun 28, 2017 9:42 pm


I replied to the GitHub issue before I saw this.

I will find the code and email it to you ( as admin I can find the email address you registered with)

But I apologise for the quality of the code, as it was just a quick hack to get it to work.
And, as I said on GitHub, that "library" is not really a library, it's just a collection of functions, so I think I just extracted the functions I needed and put modified versions of them into my own file

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Re: Learning about 433 MHz radios - how?

Post by turboscrew » Fri Jul 28, 2017 5:45 pm

Hmm. RSSI is till somewhat unclear - especially comparison between two bands of different widths...

But if someone else is in the situation I was when I started this thread, the probably most important things are these:
  • 0.5 <= 2*Fdev/BR <= 10 // modulation depth
  • Bitrate < 2*RXBW // oversampling rule
  • BW = 2*FDEV + BR <==> RXBW >= FDEV + (BR/2) // Carson's rule
Fdev is the (G)FSK frequency deviaton
BR is the air bit rate
BW is the bandwidth used (actually about 98% of the energy is within BW)
RXBW is the receive filter bandwidth

Note that Fdev and RXBW are one-sided.
In (G)FSK, "1"s and "0"s are sent using different frequency. The other is Fcarrier - Fdev, the other is Fcarrier + Fdev.
Also the RXBW is one-sided. The whole receive band is from Fcarrier - RXBW to Fcarrier + RXBW.
To receive well the BW needs to fit inside the Fcarrier +/- RXBW.

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