Antenna Switching for Bluetooth Direction Finding

[Siddharth Venkatesh]

Hi

I am currently trying to get the antenna switching working on the nRF52833 DK. I have an SPDT RF swtich which I want to use for switching between two antennas. I want to use one of the DFE GPIO control pins to control the RF switch. However I am having trouble with configuring the right GPIO pin. 

Currently I am using 

NRF_RADIO->PSEL.DFEGPIO[0] = 0x00000011; //(P0.17)
NRF_RADIO->SWITCHPATTERN = 0x1; // P0.17 active

I just had two questions:

1. What are the right GPIO pins to use on the board for this function. Can the pins P0.17 and P1.08 be used?

2. And how do I configure these pins correctly?

Thanks

[Dmitry]

Hi,

1. You can use any pins that is not marked as "Standard drive, low frequency I/O only" (see ch. 7.1 in product specification)

2. You didn't mention what RF switch you have, assuming it has a single control input. A switch pattern should consist of at least four entries -  one for the time before CTE, one for the reference period, next two (or more) for each sampling slot. An example of (I believe) the right config in your case:

NRF_RADIO->PSEL.DFEGPIO[0] = 0x00000011; //(P0.17)
NRF_RADIO->SWITCHPATTERN = 0x0; // before CTE - antenna 1
NRF_RADIO->SWITCHPATTERN = 0x0; // reference - antenna 1
NRF_RADIO->SWITCHPATTERN = 0x0; // slots 0, 2, 4... - antenna 1
NRF_RADIO->SWITCHPATTERN = 0x1; // slots 1, 3, 5... - antenna 2

[Siddharth Venkatesh]

Hi Thanks for that 

I am using the mini circuits ZSDR-230+ RF switch. Is this switch suitable for this function?

[Dmitry]

You can try it, though it has up to 4usec switching time - you need to set TSWITCHSPACING to 4usec and configure double-entry switching slots (0, 0, 1, 1), then each second slot hopefully will contain right IQ value.

[Siddharth Venkatesh]

Hi 
Im sorry, what do you mean by double entry switching slots (0,0,1,1). How would I do this?

Thanks

[Dmitry]

I mean that your RF switch requires 8-usec switch spacing, but the maximum value that can be configured in 52833 is 4 usec, so you can configure two slots for each antenna:

NRF_RADIO->PSEL.DFEGPIO[0] = 0x00000011; //(P0.17)
NRF_RADIO->SWITCHPATTERN = 0x0; // before CTE - antenna 1
NRF_RADIO->SWITCHPATTERN = 0x0; // reference - antenna 1
NRF_RADIO->SWITCHPATTERN = 0x0; // slots 0, 2, 4... - antenna 1 switching
NRF_RADIO->SWITCHPATTERN = 0x0; // slots 0, 2, 4... - antenna 1 sampling
NRF_RADIO->SWITCHPATTERN = 0x1; // slots 1, 3, 5... - antenna 2 switching
NRF_RADIO->SWITCHPATTERN = 0x1; // slots 1, 3, 5... - antenna 2 sampling