I have my PCB that I have SIM800c module with Bluetooth V3. My module GSM is working perfectly but my BT has just a few centimeters board (I have tried 3 different modules after upgrading their firmware to enable its BT!

Items I have already tried with no effect at all!

  1. mounting sim800c without any other power units on the board and feeding IC directly from outside.
  2. I have tried to wire it out directly from its related pin and cut its trace on the board and connect to different antennas but no change at all:

a) with a sprint b) wire with a plate C) wire it to one other BT module's antenna C2541 d) Add 10pf capacitor in middle of wire in one other step e) Try a computer TV antenna

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In its datasheet it is written some points: Keep the RF traces impedance as 50Ω Antenna matching circuit should be close to the antenna R201, C201, C202 are the matching circuit, the value should be defined by the antenna design. Normally R201 is 0R, C202 and C201 are not mounted.

Also note that I have seen some circuits for other similar boards with to many cap and resistors and some with nothing at all! just a connector. So I have no idea how to add them and if they will help in my case! See following example that I have found.

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Now the question is since I am very beginner for antenna topics how should I "design Antenna matching circuit"? Why while I have tried all these no change has happened at all! Even I couldn't increase its board for 30cm! I have read many related topics on the internet but could not get what to do exactly and step by step! which capacitor and resistor to use! Also is there anyway to make it better before redesign a new board and try! because it is time consuming and costly to try to see if it works or not!

I really need help, thanks.

Sim800 Datasheet: https://www.waveshare.com/wiki/File:SIM800C_Hardware_Design_V1.05.pdf Page37 is for BT antenna

  • 1
    Have you tried adjusting power with AT+BTLPWR=? What/How are you testing? Advertising from your board and scanning from another device or the opposite? Note that from what I understand, the SIM800c only supports classic Bluetooth, not Bluetooth Low Energy (aka BLE aka Smart Bluetooth), so it won't be visible with a BLE scanner app on a phone for instance.
    – jcaron
    Commented Mar 3, 2021 at 17:10
  • A quick search found the "SIM868 RF Design Application Note", which explains exactly what you need to do, but RF design is a very complex area, and you really should have access to some very expensive test gear to prove your design, and ensure it conforms to the required standards. Best advice: use a pre-tested wireless module, and don't modify its RF circuitry.
    – jayben
    Commented Jun 17 at 17:53

1 Answer 1


Have you read this one already ?


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