Approximately what RSSI/SNR should I be getting here?

Using Arduino Networking, Protocols, and Devices
1

Hi

I have two RFM95 Lora radios (915mhz). I have them in LOS about 30 metres away and I am using the following settings:

  1. frequency = 915E6;
  2. tx power = 20;
  3. spread factor = 12;
  4. bandwidth = 125E3;
  5. coding denom = 5;

Both radios have 915mhz aerials connected.

I am currently getting an RSSI of -95 and an SNR of 3. Is this about what I should expect? Appreciate that it varies on other conditions but would be good to know that its about right.

Thanks

2

I would expect SNR to be higher so close, 9 or 10dB.

RSSI is a little low also.

Could be the antennas.

3

Thanks

I'm using this antenna - is there any reason why I shouldn't use these (says it works to 915mhz)?

I suspect that I may not have soldered the ufl connector on to the board correctly. A bit fiddly given how small they are.

4

First reason is it is too long for 915 mHz. Second is at 868, is has 2DBi gain which in reality is an actual loss of 1 dbi compared to a dipole antenna with 3dbi gain.
Paul

5

ok thanks, any recommendations for something equivalent which is better?

6

Mouser sells this one: and has actual gain
They have then in stock.
Paul

7

Much easier when trying to work out if an RF device is working well or is not is to use a basic antenna, i.e. a bit of wire that is 1/4 wavelength long at the appropriate frequency.

Any other comparision depends on the purchased antenna being what it claims to be and the only way to be sure of that is to use an antenna tester and then a field test to verify the radiation pattern.

A simple bit of wire of the right length is going to perform more or less the same for everyone, the wire type is not critical, and its a universal comparison standard.

8

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