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LoRA measuring antenna's

Building antenna's is one thing, but how do you know if they are working well?

SWR can be measured with antenna analyzers like the RigExpert AA-600  (which when connected to the computer can work up to 1.4Ghz), but SWR doesn't say anything about gain.

When you want to measure gain, a good way is to have a transmitter and receiver setup in the field (for example 40m appart clear view). For the baseline measurment, for example 10 measurement to average the RSSI,  you use 2 groundplane antennas (with a gain of 0dB over a dipole). When the transmitter antenna is changed to a unkown antenna, the reception should get better (RSSI increasing) of worse (RSSI decreasing).

The setup

To do this kind of testing you can buy a very good (and expansive) signal generator and a calibrated signal meter or spectrum analyzer. But because it's a hobby we want to keep things affordable.

IMHO this should be possible with a setup of 2 Ardino's and 2 RFM95W LoRA trancievers which I used to experiment with (see my LoRA DIY page). One Arduino (the server) and will listen to transmissions of the the other Arduino (the client). The server will responde to the client message by sending back the reception RSSI that moment. The client will log this info (incl his own RSSI) so the user can determin of the new antenne is better then the reference one.


Based on the description above and my experience RadioHead Packet Radio library (which I used for my experiments), I used the rf95_client and rf95_server samples as a bases to start the test client and server. After a hour coding and testing everything was ready for the first test.

The test is simple.

  1. The server and client have the same configuration.
  2. The server is waiting for a message from the client.
  3. The client sends a '?'  to the server.
  4. The server response with the lastRssi.
  5. The client stores this value and his own lastRssi in to a array.
  6. The clients repeats this test 10 times
  7. The client calculates the average of the 10 samples and dumps the samples and the calculated average to the serial port.

 

Now it time to do some test and get results.