NRF24L01 Continuous Carrier

[ToBeDD]

Hi Forum,

I'm using a NRF24L01 (without "+") in  a very power critical application. To tune the matching networks, i used a mini coaxial connector on the output to measure Antennaimpedance and output impedance of the nRF. For that I need an unmodulated carrier to be transmitted from the nRF. I found This document which pointed out a very simple procedure to get the nRF to a CW. Start the nRF -> PWR_UP to 1 -> set highest Bit in RF_SETUP to activate CW Mode and then pull CE high. I've validated my uC Code with an osciloscope to check if the SPI protocol ist setup correctly - and it is. 
Sadly my nRF Chip does absolutely nothing. 

I've recognized that the document is for the NRF24L01+... is the NRF24L01 capable of sending CW? Due to several pages on the web, the L01 and the L01+ are similiar beside the plus version has more modulation capabilities. 

How can I achieve a constant carrier? 

FYI: I know that sending a CW at this frequency is not allowed. But that's why im using a U.FL connector to measure the carrier (with antenna disconnected). Besides that, im working in an anechoic chamber. 

Kind regards, looking forward for your help! 

Tony

[ketiljo]

Hi Tony

The procedure for setting up a carrier is the same for the + and non + devices. The only difference between the two is that the + version can do data in ACK packets plus a few more minor thing.

If the procedure doesn't work, there's something going on with your design. Can you post the schematic for the nRF24L01 part and the 16 MHz crystal spec please?

Ketil

[ToBeDD]

Hi Ketil,

thank you for qour quick reply.

Meanwhile I've implemented the "Appendix C" Procedure from Datasheet REV2.0 which worked first try. This also proves that the SPI and my Codebase is in working condition. 

For the schematic: I've used the reference design from datasheet REV2.0 "Appendix D". My Crstal is a 16MHz Type (ABM11-16.000MHZ-B1U-T from Abracon). It runs with a nice sinusodial at perfekt frequency (verified with scope). 

Is there something else that could go wrong here? 

Thank you in advance!

Tony

[ketiljo]

Hi Tony

Is this the crystal you're using? https://www.digikey.com/en/products/detail/abracon-llc/ABM11-16.000MHZ-B1U-T/9997511

If so, the CL value is 10 pF. The load caps are calculated as follows: 

Ccap = CL *2 - Cpin, where C pin = ~2 pF

For a 10 pF crystal, the caps should then be 18 pF. 

When you touch the crystal with a probe, the capacitance in the probe will pull the frequency. The best way to check the frequency of the crystal is to use a spectrum analyzer and measure the exact frequency of a unmodulated carrier. 

cheers,

Ketil