Replace Embedded Antenna with Coaxial Cable

[Husky_xc]

I am now using nrf51822 chip connected to a 50-ohm nominal input/conjugate match balun and then connected to an Embedded antenna.

I am requested to do a radio test which needs a coaxial cable out from our PCB. Is there any way that we can replace the antenna without changing PCB layout? like unsolder the antenna and then attach a coaxial cable? If yes how to choose the components?

Thanks

The spec for balum and antenna are here: media.digikey.com/.../1001312_May2013.pdf www.st.com/.../en.DM00087690.pdf

[Jørn]

Hello Husky_xc

You can solder the center conductor of a semi-rigid, 50 Ohm, coaxial cable directly to the transmission line coming out from the balun, however you need to take some precautions.

The coax will need to be soldered as close as possible to the balun, preferably less than 1mm away. The exposed center conductor of the coax will need to be as short as possible as well. This is important because the exposed conductor will not have a characteristic impedance of 50 Ohm due to the absence of the dielectric and the ground shield.

The ground shield of the coax will need to be soldered to the ground plane of the PCB. Keeping the ground shield as short as possible, while making a solid connection with the ground plane.

If the 16MHz crystal is close, and you need a stronger connection between the ground shield and the ground plane (to prevent it from coming loose due to mechanical strain) you can also solder the shield to the casing of the 16MHz crystal.

The transmission line leading to the antenna will need to be cut as close to the center conductor of the coax as possible. If you leave the transmission line attached it will act as a transmission line stub, which will interfere with your measurements.

Best regards

Jørn Frøysa

[Husky_xc]

Hi Jørn, thanks for the answer, that's really helpful! I will try it out see if there are any extra questions.