Author Topic: How many non-overlapping Moteino channels exist if datarate is 200kbps?  (Read 1606 times)

WhiteHare

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The RFM69 datasheet does not seem to explicitly answer the question, though perhaps to someone with more knowledge than me maybe it answers it implicitly.

Anyone know the answer?
« Last Edit: September 09, 2015, 06:04:08 PM by WhiteHare »

emjay

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Re: How many non-overlapping Moteino channels exist if datarate is 200kbps?
« Reply #1 on: September 12, 2015, 05:32:55 AM »
An answer requires also specifying which country-specific ISM band is in use and what frequency deviation is applied in each channel.

WhiteHare

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Re: How many non-overlapping Moteino channels exist if datarate is 200kbps?
« Reply #2 on: September 12, 2015, 09:57:49 AM »
915Mhz

emjay

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Re: How many non-overlapping Moteino channels exist if datarate is 200kbps?
« Reply #3 on: September 12, 2015, 10:44:37 AM »

The formula you need to use is on p.32 of the SX1231H data sheet:

  BW20dB = 2 (FDEV + BR/2)

That gives an approximation for the width of the occupied channel (without guard bands, allowance for main crystal precision/drift, transmit spurs etc) so is the tightest you could expect to pack channels together and expect success.
You then need to map this against the FCC bandplan for that ISM band.  There are several zones with differing rules about maximum radiated power, duty cycle etc. so that is quite an exercise.

Of course, as a shared resource, you have no guarantee that any particular "channel" is unoccupied at any point in time or that other users are following the duty cycle requirements.
 

WhiteHare

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Re: How many non-overlapping Moteino channels exist if datarate is 200kbps?
« Reply #4 on: September 12, 2015, 08:29:27 PM »
Because I need a concrete, non-hedged answer, I just now tried measuring it with an RTL-SDR.  Including the guard bands,  it looks as though its about 500KHz wide.



« Last Edit: September 12, 2015, 11:40:00 PM by WhiteHare »

Felix

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Re: How many non-overlapping Moteino channels exist if datarate is 200kbps?
« Reply #5 on: September 14, 2015, 08:45:09 AM »
There is no straight answer because it depends on your radio settings. The bandwidth will dictate how many channels you get. Divide your total spectrum by the bandwidth and you get a number that you're probably looking for. So if your bandwidth is 500khz and you have 26mhz of spectrum then you got 52 channels.