When visiting Bluetooth usage page just now [here] (Bluetooth Usage | Seeed Studio Wiki) I noticed that it asks to connect the Antenna that comes with the purchase of xiao esp32-c3, to use WIFI or Bluetooth always.
I did some experiments for BLE signal strength without external antenna and compared them to the esp32-c3 super mini that I also have which has a ceramic inbuilt antenna.
The test was using NRFConnect on Android mobile to understand signal strength and noticed, the super mini when is held next to mobile running NRFconnect gives a signal strength of -33 dBm, while xiao esp32-c3 gives around -60dBm. When held around 40 cm apart the supermini drops to -75dBm while xiao drops to -95 dBm.
That brings a few questions to my mind.
What is a signal strength that is still in a good range to have a stable BLE connection between the paired contacts for xiao? On other hand, I have one more xiao board, that does not show any BLE signal, on NRFconnect. Does that mean it has defect in BLE or some other defect? and if one board out of two random boards has a defect, does that indicate quality production issues for xiao for bulk order purchases in the future?
Another question is why unlike super mini Seeed studio xiao has preferred the external antenna, and not included inbuilt ceramic antenna which still stays super compact and as super mini shows has a strong strength for close distances unlike xiao, because an external antenna hanging around takes the compactness away in related applications where form factor is critical.
Hi there,
Albeit , most would agree on the compactness issue, However If you look at the Super mini you will see there is a lot of (KEEP-OUT) Zone on the PCB. The Xiao and Seeed didn’t have the real-estate to do it the same. The FCC test and Part B & C require compliance at particular distance and power level. The External antenna give you a lot of latitude in range for different TX power dB.
Be sure of the BSP file you use and which LIB’s there may need to be extra steps to compare apples to apples. 
there is a video demo of some BLE range testing on here with code used. Have a peek at that as well.
HTH
GL 
PJ 
1 Like
Thanks for the answer.
If some one wants to design their own C3 based board because they want a smaller form factor antenna onboarded board that can have some flexibility in terms of size, as long as its around size of super mini, but with battery support, and onboard strong antenna, do you recommend any materials that needs to be compulsorily kept in mind in terms of guidelines from compliances, regulations etc and where can one read about this if a new board needs to be designed from scratch that basically can use c3 chip and firmware but lays out components onboard without any issues. Any references can be great if you can provide please.
Hi there,
Look to the C6 it’s all of the C3 and more… Has the antenna diversity to.
The Super Mini is pretty much as small as you can get commercially available, for C3 specs AFAIK, I think there’s one that is just a bare C3 and a pinch of components with ANt in PCB. check out these …
and search this in images, on G-man , some good hits there too.
“ESP32C3 module only with ant and a resistor”
(animated gif from google, FYI) 
You may need to press Play!
HTH
GL PJ
This is One…
1 Like
Thanks. I will check this soon.