See tutorial on https://goo.gl/H8i0rT

_33_nRF24L01_SimpleTransmitRadio.ino

/*
   Project name: nRF24L0 — Popular RF module using with Arduino ! #arduSerie-33
     Studing nRF24L01 radios!
     Flavour I - Transmiter Radio
     Hex File: _33_nRF24L01_SimpleTransmitRadio.ino
   Revision History:
     Jun, 2017
       - Medium webpage: https://goo.gl/H8i0rT
   Description:
          This is a simple code to configure a radio transmitter and other receiver
          in the simplest possible way!
   MCU:                  Arduino 1.8.2 - @16MHz       http://www.arduino.cc/
   Radio:                nRF24L01  - Unknown version
   Connections:
      See Official youtube channel vids:
   Based on:  Connecting and programming nRF24L01 with Arduino and other boards
               from http://starter-kit.nettigo.eu/2014/connecting-and-programming-nrf24l01-with-arduino-and-other-boards/

   Datasheet Atmega328P  8-bit AVR Microcontrollers:
   http://www.atmel.com/Images/Atmel-42735-8-bit-AVR-Microcontroller-ATmega328-328P_Datasheet.pdf

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License v3 as published by
   the Free Software Foundation
*/

#include <SPI.h>
#include <nRF24L01.h>
#include <RF24.h>

RF24 radio(7, 8);

const byte rxAddr[6] = "00001";                // you can modify this address
                                               // serves to mark each transmission line

void setup()
{
  radio.begin();                               // initializa the serial interface
  radio.setRetries(15, 15);                    // 15 * 255 = 3.75 milliseconds to retry transmition, 15 tries
  radio.openWritingPipe(rxAddr);               // open a stream for transmitting the data pipe

  radio.stopListening();                       // stop the process of listening
}


void loop()
{
  const char text[] = "Hello World from J3";   //Send a message
  radio.write(&text, sizeof(text));            // write to radio stream

  delay(1000);                                 //wait one second
}