That scanner example you gave me is brilliant. Its worth sharing the results to show not only how to transmit constant carrier, but also how to use the receiver to monitor activity in the WiFi spectrum. I'm very impressed.
The nRF24L01+ device has a built-in low noise amplifier. So with just a short quarter wave stub antenna, it can pickup any local WiFi activity that may be taking place. The sketch first prints details of the device itself, but then goes on to display a complete scan of the 2.400 to 2.525 GHz spectrum.
You have to be aware that this Tx/Rx module is not directly WiFi compatible. So it won't talk to a WiFi router, or decode WiFi packets. The radio channel numbers mentioned differ from WiFi channel numbers, and the modulation used is also different. The module uses GFSK modulation and has channel numbers that are 1 MHz wide, so there are a total of 126 channels going from 2.400 GHz to 2.525 GHz.
The example sketch will auto scan every channel in turn (0 - 125) and then display the received channel signal strength as a hex digit (0 - F). Here is a sample scan that I made this evening...
Where I have annotated the picture with an arrow, you can see the point where I switched on the constant carrier on channel 40 from a second nRF24L01 module, placed only a few feet away. But noticed that there is radio signal activity received before it was switched on.
Notice too that there is no radio signals appearing above Channel 100. This is equivalent to 2.500 GHz, which is beyond the WiFi channels (WiFi CH14 = 2.484 GHz).
My construction for this experiment is shown below. I built the plywood bases originally to use for the ADF4351 Signal Generator modules, but I decided to use the same SPI bus for the nRF24L01 modules. I use different pins for Chip Select etc, and switched the SPI clock from pin 13 to pin 14, but it worked a treat on first switch on.