This is an interim report on some experiments with BLE regarding the effects of RF switch power on/off and antenna selection.
The conditions are as follows
- Receiver side turns on RF switch and uses an external antenna
- Transmitter side, RF switch is on or off, and an antenna is selected
- When sing an on-board antenna, an external antenna must be removed
- The distance is approximately 10 meters over a wall
The results are summarised in the graph below.
When RF switch is powered, an external antenna has about 10 dB advantage over an on-board antenna. When RF switch is not powered, an external antenna is about 10 dB smaller, while an on-board antenna is about 30 dB smaller.
Based on the “powered from input pins” hypothesis:
If an external antenna is selected on HIGH, it will drop by 10 dB, but appears to be working. On the other hand, when set to LOW and an on-board antenna is selected, it is 25 dB smaller, close to the data sheet isolation value of 30 dB.
This is just my hypothesis.
