PCB antenna and J1 connector

[Ceow]

Hi all,

I'm trying to measure the transmit power of nRF51 development kit with a spectrum analyzer and I am facing the following issue:

It is specified in the user guide of nRF51 that "When connecting the test probe, the internal switch in the SWF connector will disconnect the PCB antenna". However, in my case, I can still connect to the nRF51 with my phone, while an SWF connector is plugged in the board. I suppose that the trace antenna is still connected. My connection setup is like in this answer.

I was assuming that any SWF connector should work but is the one from Murata specified in the user guide the only one able to achieve this ? If not, do you have any more guidance ?

Thanks in advance

[AmbystomaLabs]

I will assume you are using the correct mating connector. For reference this is the correct one: www.murata.com/.../o33e.ashx

There are a lot of knock-offs of these connectors, so it is entirely possible you have one that isn't from MuRata, but likely works fine.

None of these connectors will fully isolate the nRF from its local environment. All the microstrips, components, the SWF, and even the nRF itself will radiate some RF and allow your phone to connect locally.

What you will see is that the signal strength and thus range will be severely diminished.
However, when nearby even an nRF with no RF connection will still connect just from the signal that radiates from the chip.

[AmbystomaLabs]

So, we're done here right? It doesn't matter even if you use the MuRata part, your phone will still connect when local to the board.

[Ceow]

I think so. I was able to measure a signal strength of ~ -45dBm from my phone instead of a severely diminished signal as you said. So I suppose that something is wrong with the connector I was using but I ordered the one from MuRata and hope that it will work.

[Ceow]

Thank you AmbystomaLabs

[AmbystomaLabs]

Yeah, -45dBm is pretty high. I just wanted to point out that there could be some confusion on the connector. The DK connector is the version that has the switch inside to reroute the signal. A standard SWF connector does not. MuRata sells both as do other companies. The male connector for the test port with the switch is different from the standard connector since the pin is longer to engage the switch. So, it is possible you were using a standard swf connector but since the long pin wasn't there the switch was not engaging. So, just to be clear the model number for the probe is MXHS83QE3000. And here is the digikey page: www.digikey.com/.../en

The connector is actually a little clumsy to use standalone since they are designed to be installed in test jigs for production testing. You normally end up having to hold the thing the whole time.