BLE Antenna and capacitors

[Damien Berger]

Hi, 

we are using the NRF52840 DK and we would like to use our own antenna. We saw on others posts that we have to connect it to the J1 connector's place.

 We have some doubts :

When we connect a multimeter (beeping mode) on the two sides of capacitors C22 it beeps, do you know why ? A capacitor is not supposed to beep, right ? That happens with a lot of others capacitors and we do not understand why.

Then, if we use the multimeter between the RF signal (left of connector J1) and ground (at the bottom of the connector J1) it also beeps. Is it normal ? should'nt it be isolated ? 

Regarding the use of our own antenna, if we remove the J1 connector and directly connect our antenna to the RF signal, the actual antenna (ANT) will be disconnected right ?

Is there anything else we have to take into account in order to use our antenna ?

Thank you.

[ketiljo]

There's a transformer (balun) on chip. One side of the secondary winding is connected to the ANT pin and the other to ground. So you will measure a DC short between the ANT pin and ground. L1 will also have a DC short.

If you insert a connector in to J1, the right hand part will be disconnected and the connector will be connected to C22. 

 

[Damien Berger]

Thank you, any idea about my others questions ?

[ketiljo]

You will measure low resistance to ground on the top side of C22 because the current will flow through L1 into the ANT pin and to ground. The whole antenna path is DC grounded. 

A normal capacitor may have low resistance until it's charged by the multimeter. So it will beep for a short while.

Just go ahead and connect the antenna to J1. It's supposed to be like this. You don't need to remove J1, just use a test probe, see this