nRF24L01 Notes by DL4YHF

Original file location: ?/datasheets/PLL_and_RF_Special_ICs/nRF24L01/DL4YHF_nRF24L01_Notes.htm
Online on the website: www.qsl.net/dl4yhf/nRF24L01/DL4YHF_nRF24L01_Notes.htm

The nRF24L01(+) attracted the author's attention because it's widely available on a small module with either an antenna printed on the PCB, or even with a small on-board "power amplifier" / "low noise amplifier".
A couple of those development boards was ordered from a various suppliers, with qualities ranging from 'non-functional crap or fake chips' to 'perfect':

A batch of "NRF24L01+, PA + LNA Wireless Modul ~1100m Reichweite, mit Antenne" from the first shop (without an RF shield) was complete crap;
From a batch of "NRF24L01 + / CC1100/CC2500/A7105" modules (without the RFX2401C "PA / LNA"), some worked, others didn't, also identifyable by a low resistance between MISO and GROUND when not powered - more on that later.
A batch of EBYTE "nRF24L01 + PA + LNA" modules (E01-ML01DP5, with metal RF shield and SMA connector for the antenna, shown below) worked right out of the box (also in "CW", thus really populated with nRF24L01+), and produced +18 dBm when powered with +3.1 Volt DC.

Photo of the EBYTE "nRF24L01 + PA + LNA" module (E01-ML01DP5).
Click on image to magnify.

The module with 'PA + LNA' draws significantly more DC current that then 'bare' "nRF24L01+" module (without the bidirectional amplifier chip). Thus, for the planned "QRPP 13 cm CW beacon", some bare modules were ordered, too. On the second attempt, a seller (AZ-Delivery) was found who really had the PCB populated with a genuine nRF24L01+ chip.

nRF24L01 General Info and locally saved datasheets
1. nRF24L01(+) Datasheets
2. nRF24L01 Info Links
nRF24L01 Hardware, Host Interface, Pinouts
nRF24L01 Continous Wave Mode (e.g. beacon or signal generator)
1. Registers to control CW mode, power, frequency

1. nRF24L01(+) General Info and locally saved datasheets

Difference between both chips (with and without the "+" suffix),

The nRF24L01 is a single-chip wireless transceiver chip produced by Nordic Semiconductor. Its radio frequency band is between 2.4GHz and 2.5GHz. This frequency band also belongs to the license-free ISM (Industrial, Scientific and Medical) ...
There are modules such as nRF24L01 module, nRF24L01+ module, nRF24L01+ PA/LNA module.

They are actually similar, nRF24L01+ is an upgraded version of nRF24L01 chip.
nRF24L01 only supports 1Mbps and 2Mbps transmission rate, while nRF24L01+ also supports 250Kbps transmission rate.
The '+' variant features a lower data rate mode, superior sensitivity, better regulatory compliance, and increased communication reliability.

The nRF24L01+ PA/LNA module is an external antenna signal module that integrates transceiver amplification on the basis of the nRF24L01+ module, which increases the transmission distance of the module. In an open environment, the maximum transmission distance of the nRF24L01/nRF24L01+ module using the on-board PCB antenna is only 100 meters, while the PA/LNA module can reach 1000 meters.

1.1 nRF24L01(+) Datasheets

nRF24L01+PA+LNA 2.4GHz RF Transceiver Module.pdf: From 'Handson Technology':

This module based on Nordic nRF24L01+ with integrated Power Amplifier (PA) and Low-Noise-Amplifier (LNA) for extended range of up to 1,000 meter. This transceiver IC operates in the 2.4GHz band and has many new features! Take all the coolness of the nRF2401A and add some extra pipelines, buffers, and an auto-retransmit feature. You can use it in you project without any wireless design, just need to leave a 8 pins interface to this module, use the SPI interface to control the module on transferring data.
nRF24L01plus_Product_Specification_1_0.pdf: Sheds some light on difference between the "+" and "non-plus" chips:

nRF24L01+ is drop-in compatible with nRF24L01 and on-air compatible with nRF2401A, nRF2402, nRF24E1 and nRF24E2. Intermodulation and wideband blocking values in nRF24L01+ are much improved in comparison to the nRF24L01 and the addition of internal filtering to nRF24L01+ has improved the margins for meeting RF regulatory standards.
(draw your own conclusions about 'meeting RF regulatory standards' of the "non-plus" chips..)
NRF24L01_old_preliminary_product_specification.pdf
nRF24L01 Product Specification V2.0 (anno 2007)

1.2 nRF24L01 Info Links

https://forum.arduino.cc/t/simple-nrf24l01-2-4ghz-transceiver-demo/405123

Introduction to the RF24 library

https://github.com/nRF24/RF24/blob/master/COMMON_ISSUES.md

Contains helpful notes for troubleshooting with the 'RF24' class driver from Github, e.g.:

My PA/LNA module fails to transmit
You may find variants of the nRF24L01 transceiver that are marketed as "nRF24L01+PA+LNA" (WB: The ones used here). These modules are distinct in the fact that they come with a detachable (SMA-type) antenna. They employ separate RFX24C01 IC with the antenna for enhanced Power Amplification (PA) and Low Noise Amplification (LNA) features. While they boast greater range with the same functionality, they are subject to a couple lesser known (and lesser advertised) drawbacks:

Stronger power source (...)
Needs shielding from electromagnetic interference.(...)

My PA/LNA module doesn't perform as well as I'd hoped or the NRF radio works better on touching it
As described above, the radio modules (notably the PA+LNA versions) are reliant on a stable power source. While these modules may work with a poor power supply, they often lose packets or fail to receive as many as a module with a better power source. Moreover, this can sometimes be seen in odd ways such as the radio module working better when touched. This again is likely a power stability issue because the radio module is missing a capacitor (a commonly neglected expense on behalf of the module's manufacturer).

Add capacitor(s) close to the VCC and GND pins of the radio. Typically, 10uF is enough. Depending upon your circuit's layout, differences in capacitors' electrolytic properties can be seen, such that a low ESR (Equivalent Series Resistance) rated capacitor is desirable.

2. nRF24L01 Hardware, Host Interface, Pinouts

Interface pinout of the 'nRF24L01+ PA/LNA' board (top view, from the 'Handsontec Transceiver Module)

Since none of the originally purchased 'nRF2401+ PA/LNA' boards was working properly (*), it was time to take a "closer look" at the board. So here it is, with the IC pins numbered (red) and some important signal lines (PCB traces marked white):

Layout of the 'nRF24L01+ PA/LNA' board. Click on image to magnify.
Many of these boards floating around the planet are crap (*).

The (faulty) PA/LNA is a Skyworks RFX2401C "2.4 GHz Front-End Module", SMD part marking "2401C". The datasheet is widely available. Pins on the 3*3 mm QFN-16 IC are:


                          Vdd NC Vdd DNC 
                       ,-----------------,
                       | O 16 15  14 13  |
                    NC |1    ......... 12| NC 
                       |    .        .   |
                   GND |2  .  (17)   . 11| GND
                       |   . GND/    .   |
                   GND |3  . COOLING!. 10| ANT <----> to/from PI-filter <---> Antenna
                       |   ...........   |     RX  TX
           <----> TXRX |4               9| GND
           RX  TX      |   5   6   7  8  |
                       '-----------------'
                         TXEN RXEN NC GND    __
                           |   '------------|__|--<-- from nRF24L01+ "CE" (H=ChipEnable)
                           |                 __
                           '----------------|__|--<-- from nRF24L01+ "Vdd_PA" (H=TX, L=RX)
                        Skyworks RFX2401C    (resistors should be 10 k, but were populated with 1 kOhm)
  Note: "NC"  = Not Connected,
        "DNC" = "Do Not Connect" !

About the non-functional boards from a German reseller:: Three of the four boards had a dead nRF24L01+, easily identifyable by measuring the impedance between MISO and ground before powering on the device, which was around 45 Ohm.
The only board with a working nRF24L01+ one had a dead "PA/LNA"-chip and produced a maximum output of -3 dBm at the highest power setting.

Above: Larger board with integrated PA (power amplifier for TX) and LNA (low-noise amp for RX).
Below: Smaller board with integrated antenna (printed to the PCB), without amplifiers.

Interface pinout of the 'nRF24L01+' board without "PA/LNA", but with on-board antenna.
Maximum output = 1 mW, thus only for short-range experiments. SPI adapter is compatible.

Unfortunately the first 'nRF24L01+' boards were NOT populated with an nRF24L01+, but with the older nRF24L01 (without "+"). So it was unusable as a low-power "CW beacon", and it doesn't support the long-range "low" speed with 250 kBit/second.
The author had more luck on the second attempt, this time with modules from a different reseller in Germany (AZ-Delivery, but that seller went out of business in 2026):

Foto of what the author believed was a 'genuine' nRF24L01+
on the 'black board' with integrated Meander-style PCB antenna.
The board with this chip produced the spectrum shown below.

Spectrum and Power Test from a "black board" with integrated Meander-style PCB antenna.
-47 dBm measured via DSA with a dipole antenna - see details about the test setup below.

For the above "Power Test" of the PA-less module, the receiver (DSA = Digital Spectrum Analyzer) was located 50 cm away from the board, using a 2.4 GHz swivel dipole antenna (10 cm long) from the "nRF24L01+PA+LNA" boards. The nRF24L01+ was configured for Continuous Wave, and 1 mW output (the maximum), using the author's "QRP CW Beacon" firmware running on a PIC16F628A.
Peak power : -47 dB
Peak frequency: 2.40195 GHz.
During the first minute after power-on, frequency drift could be seen on the DSA, even at a display span of 500 kHz. This is caused by the cheap 16 MHz crystal being heated up (very moderately) by the nRF24L01+. Not an issue for wide-band FSK transmissions at the chip's supported bitrates (500, 1000, and 2000 kBit/second), but too unstable for serious 'narrow band' modes like CW / Morse code in amateur radio...
... but besides that, trying a CW QSO via the geostationary satellite QO-100
using an nRF24L01+ with "PA" (RFX2401C) and a tweaked 16-MHZ crystal would be fun !
(more on CW mode, and its applications in chapter 3)

2.1 nRF24L01(+) Pin Functions

From the nRF24L01+ datasheet (Rev 1.0, page 11):

IC PIN BOARD PIN Name Pin function Description

1 3 (!) CE Digital Input Chip Enable Activates RX or TX mode

2 4 (!) CSN Digital Input SPI Chip Select

3 5 (!) SCK Digital Input SPI Clock

4 6 (!) MOSI Digital Input SPI Slave Data Input

5 7 (!) MISO Digital Output SPI Slave Data Output, with tri-state option

6 8 (!) IRQ Digital Output Maskable interrupt pin. Active low

7 2 (!) VDD Power Power Supply (+1.9V - +3.6V DC)

8 1 (!) VSS Power Ground (0V)

IC PIN	BOARD PIN	Name	Pin function	Description
1	3 (!)	CE	Digital Input	Chip Enable Activates RX or TX mode
2	4 (!)	CSN	Digital Input	SPI Chip Select
3	5 (!)	SCK	Digital Input	SPI Clock
4	6 (!)	MOSI	Digital Input	SPI Slave Data Input
5	7 (!)	MISO	Digital Output	SPI Slave Data Output, with tri-state option
6	8 (!)	IRQ	Digital Output	Maskable interrupt pin. Active low
7	2 (!)	VDD	Power	Power Supply (+1.9V - +3.6V DC)
8	1 (!)	VSS	Power	Ground (0V)

2.2 nRF24L01(+) Host Interface

The nRF24L01(+) datasheet doesn't explicitly specify the SPI "mode".
So which of the four "SPI Modes" ( 2 * CPOL + CPHA) does it use ?

Mode CPOL CPHA SCLK Idle Data Sampled On Data Shifted On

0 0 0 Low Rising Edge Falling Edge

1 0 1 Low Falling Edge Rising Edge

2 1 0 High Falling Edge Rising Edge

3 1 1 High Rising Edge Falling Edge

Mode	CPOL	CPHA	SCLK Idle	Data Sampled On	Data Shifted On
0	0	0	Low	Rising Edge	Falling Edge
1	0	1	Low	Falling Edge	Rising Edge
2	1	0	High	Falling Edge	Rising Edge
3	1	1	High	Rising Edge	Falling Edge

From the nRF24L01+ datasheet (Rev 1.0, page 52):

nRF24L01+ SPI read- and write operation. C7..0=COMMAND, S7..0=STATUS, D15..0=DATA.

-> Looks like "SPI Mode 0" (CPOL=0, CPHA=0):
Clock low on idle, data sampled on rising edge, data shifted on falling edge.

3. nRF24L01(+) Continous Wave Mode (e.g. beacon or signal generator)

From a thread at www.eevblog.com/forum/rf-microwave/zero-effort-2-4ghz-cw-beacon-with-switchable-frequency:

nRF24L01+ (which is dirt cheap) has a CW mode, with programmable CW frequency and amplitude. Used that a couple of times, mostly as a quick sanity check for SDR + Rx antenna + cable integrity. Though, it will take some time to wire, to power and to program a chip.
(...)

There are ready made modules with nRF24L01+ and a PCB antenna. Some modules also have an UFL connector, for an external antenna if needed. Note that there are some nRF24L01 (without the + at the end). I've tested the CW mode only on the nRF24L01+.

Then, you'll need a microcontroller to talk with the nRF chip. Most common and cheapest would be an Arduino Nano board. Can be bought ready made from any maker's shop, ebay, etc. Probably they are at mouser or Digikey, too, but I never searched.

Both modules come with 0.1'' pins. Wire them together with some DuPont wires, or solder them on a test board, and that's it.

For the software part, the CW mode for the nRF chip is documented in its manual, so there are plenty of ready made Arduino examples to put the nRF24L01+ in CW mode. Connect the Arduino to a PC, download the demo, and it should work.
For a ready made program, search for 'nRF24L01 continuous carrier Arduino'. Random example:
https://forum.arduino.cc/t/nrf24l01-arduino-trying-to-get-constant-carrier-wave-output-for-testing/322112/13

Often Arduino 'sketches' rely on bulky libraries. Not in this case:
continuous_carrier/continuous_carrier_Pv1.ino
Essential code (all in the Arduino-dictated "setup()"):


SPI_RW_Reg(WRITE_REG + CONFIG,0x0a);  // 1. Set PWR_UP = 1 and PRIM_RX = 0 in the CONFIG register.
       // Bit0:PRIM_RX:0(PTX) Bit1:PWR_UP:1(Up) Bits2-3:CRC:00 Bits4-6:IRQ:000 Bit7:Always0

  ... delays between register accesses omitted for clarity ...

SPI_RW_Reg(WRITE_REG + RF_SETUP,0x93); // 3. In the RF register set: CONT_WAVE = 1, PLL_LOCK = 1, RF_PWR.
       // bit0:LNA_HCURR:1, bits1-2:RFPwr:11(0dBm), bit3:DataRate:0(1Mbps), bit4:PLL_Lock:1, bits5-6:00, bit7:CONT_WAVE:1

SPI_RW_Reg(WRITE_REG + RF_CH,0x05);    // 4. Set the wanted RF channel.


digitalWrite(CE,1);  // 5. Set CE high.
                     // 6. Keep CE high as long as the carrier is needed.

3.1 Registers to control CW, power, frequency

Details about CW, frequency- and power control, from the nRF24L01+ datasheet (Rev 1.0, page 58):

Addr	Mnemonic	Bit	ResetVal	Type	Description
05	RF_CH				RF Channel
	Reserved	7	0	R/W	Only '0' allowed
	RF_CH	6:0	0000010	R/W	Sets the frequency channel

06	RF Setup				RF Setup Register
	CONT_WAVE	7	0	R/W	Enables continuous carrier transmit when high
	reserved	6	0	R/W	Only '0' allowed
	RF_DR_LOW	5	0	R/W	Set RF Data Rate to 250kbps. See RF_DR_HIGH for encoding.
	PLL_LOCK	4	0	R/W	Force PLL lock signal. Only used in test
	RF_DR_HIGH	3	0	R/W	Select between the high speed data rates. This bit is don't care if RF_DR_LOW is set. Encoding: [RF_DR_LOW, RF_DR_HIGH]:
					'00' : 1Mbps
					'01' : 2Mbps
					'10' : 250kbps
					'11' : Reserved
	CONT_WAVE	2:1	11	R/W	Set RF output power (TX)
					'00' : -18 dBm
					'01' : -12 dBm
					'10' : -6 dBm
					'11' : 0 dBm
	obsolete	0			Don't care

About what NORDIC call the 'frequency channel':
Frequency in MHz = 2400 + channel number in register 0x05, bits 6..0 .
Thus the only possible "CW carrier frequencies" are 2400 to 2525 MHz, in 1 MHz steps.