Seeking a setup for tuning the antenna for nRF51422

[henning larsen]

In short:Is it feasible to use RSSI values when tuning the antenna?

I have a custom board with an nRF51422 on which I have designed the RF part to be as much as possibly according to the development kit. I have however been obliged to change the antenna and board thickness due to space issues. So I need to adjust the antenna to obtain good matching.

I see two options: [b]1) Have nRF51422 broadcast packets and measure the RSSI in the receiver (for instance nRF2779 USB dongle - which is part of eval. and dev. kits) 2) Have nRF2779 USB dongle broadcast packets and measure the RSSI in nRF51422 from the RSSISAMPLE register. [/b]

The RSSI will in both cases be a measure of the antenna matching properties and can thus be used to find the best (not necessarily optimum) antenna length.

Both options suffer that I did not find any examples on how to read the RSSI value. Search on thisisant.com indicate that option 1) require a CC257X device when using the ANT_RSSI_Demo from thisisant.com

So I seek an example on how to read the RSSI value from either nRF51422 or nRF2779 USB dongle.

I am aware of the method described in the excellent white paper by Nordic SemiconductornWP-017 on antenna matching using Smith chart and a VNA. This is very comprehensive and require an VNA. I was wondering to use something simpler at least for a start.

On thisisant.com there is an Windows appication: ANT_RSSI_Demo which supposedly can display RSSI values, but it does not work on nRF2779 USB dongle. The error message indicates that it is requiring a CC257x chip-set device. It is a bit unclear where to get such with USB interface.

Any suggestions on practical antenna tuning are welcome. Thanks

[Ole Morten]

I'm not aware of any good setups for doing this kind of hacky antenna tuning. However, we can help with proper tuning if needed, but you have to create regular support case and upload Gerber files of your design for review first. A support case can be created with your regular MyPage account.

[henning larsen]

Ok Thanks for your answer. I will consider your proposition.

But does that mean that there does not exist example code on how to read RSSI value in nRF51422?

Could be useful though in other cases.

Manual has a brief description on the RSSI register, but I have the understanding that there is more to it than just reading the register value.

[xinhua zhu]

I am in similar situation. Any example code to read RSSI in nRF51422 for my information?