Docs: Update Radios Menu

Author: nseidle

docs/img/Terminal/SparkFun RTK Everywhere - Radios Menu.png

@@ -10,7 +10,7 @@ Torch: ![Feature Supported](img/Icons/GreenDot.png)
 
 Pressing 'r' from the main menu will open the Configure Radios menu. This allows a user to enable or disable the use of the internal ESP-Now radio.
 
-ESP-Now is a 2.4GHz protocol that is built into the internal ESP32 microcontroller; the same microcontroller that provides Bluetooth and WiFi. ESP-Now does not require WiFi or an Access Point. This is most useful for connecting a Base to Rover without the need for an external radio. Simply turn two SparkFun RTK products on, enable their radios, pair them, and data will be passed between units.
+ESP-Now is a 2.4GHz protocol that is built into the internal ESP32 microcontroller; the same microcontroller that provides Bluetooth and WiFi. ESP-Now does not require WiFi or an Access Point. This is most useful for connecting a Base to Rover (or multiple Rovers) without the need for an external radio. Simply turn two SparkFun RTK products on, enable their radios, pair them, and data will be passed between units.
 
 Additionally, ESP-Now supports point-to-multipoint transmissions. This means a Base can transmit to multiple Rovers simultaneously.
 
@@ -22,7 +22,7 @@ ESP-Now is a free radio included in every RTK product, and works well, but it ha
 
 2. Limited range. You can expect two RTK devices to be able to communicate approximately 250m (845 ft) line of sight but any trees, buildings, or objects between the Base and Rover will degrade reception. This range is useful for many applications but may not be acceptable for some applications. We recommend using ESP-Now as a quick, free, and easy way to get started with Base/Rover setups. If your application needs longer RF distances consider cellular NTRIP, WiFi NTRIP, or an external serial telemetry radio plugged into the **RADIO** port.
 
-3. Bug limited to Point to Point. There is a known bug in the ESP32 Arduino core that prevents a base from [transmitting to multiple rovers](https://github.com/espressif/esp-idf/issues/8992). This will be fixed in future releases of the RTK firmware once the ESP32 core is updated. For now, a base can be paired successfully with a single rover.
+3. ESP-Now can co-exist with WiFi, but both the receiver and transmitter must be on the same WiFi channel. 
 
 ## Pairing
 
@@ -34,10 +34,26 @@ On devices that have a display, pressing the Power/Setup button will display the
 
 *Radio configuration through WiFi*
 
-The radio system can be configured over WiFi. The radios subsystem is disabled by default. Enabling the radio to ESP-Now will expose the above options. The unit's radio MAC can be seen as well as a button to forget all paired radios. This button is disabled until the 'Enable Forget All Radios' checkbox is checked. The 'Broadcast Override' function changes all data transmitted by this radio to be sent to all radios in the vicinity, instead of only the radios it is paired with. This override feature is helpful if using a base that has not been paired: a base can transmit to multiple rovers regardless if they are paired or not.
+The radio system can be configured over WiFi. The radio subsystem is disabled by default. Enabling the radio to ESP-Now will expose the above options. The unit's radio MAC can be seen as well as a button to forget all paired radios. This button is disabled until the 'Enable Forget All Radios' checkbox is checked. The 'Broadcast Override' function changes all data transmitted by this radio to be sent to all radios in the vicinity, instead of only the radios it is paired with. This override feature is helpful if using a base that has not been paired: a base can transmit to multiple rovers regardless if they are paired or not.
 
 ![Radio menu showing ESP-Now](<img/Terminal/SparkFun RTK Everywhere - Radios Menu.png>)
 
 *Radio menu showing ESP-Now*
 
-A serial menu is also available. This menu allows users to enter pairing mode, view the unit's current Radio MAC, the MAC addresses of any paired radios, as well as the ability to remove all paired radios from memory.
+A serial menu is also available. This menu allows users to enter pairing mode, change the channel (ie, set of frequencies) used for communication, view the unit's current Radio MAC, the MAC addresses of any paired radios, as well as the ability to remove all paired radios from memory.
+
+## Setting the WiFi Channel
+
+![Radio menu showing ESP-Now](<img/Terminal/SparkFun RTK Everywhere - Radios Menu.png>)
+
+*Radio menu showing channel 11*
+
+All devices must be on the same WiFi channel to communicate over ESP-Now. Option **4 - Current channel** shows the current channel and allows a user to select a new one. Allowable channel numbers are 1 to 14. By default, devices will communicate on Channel 1. A user may select any channel they prefer.
+
+**Note:** ESP-Now can operate alongside WiFi but the user should be aware of the channel numbers of the devices. When a device connects to a WiFi network, the ESP-Now channel number may be altered by the WiFi radio so that the RTK device can communicate with the WiFi Access Point.
+
+Using a single device to communicate corrections to multiple devices (no WiFi involved) is the most common use case for ESP-Now.
+
+Using ESP-Now with a single device on WiFi is possible. Take the example of a Base that needs to communicate corrections over ESP-Now and will also be pushing the corrections to a Caster over NTRIP using WiFi: The Base is started, WiFi is activated, and the channel is overwritten to 9 (for example) when the device connects to the Access Point. All rovers in the area who wish to obtain corrections over ESP-Now also need to have their channels set to 9.
+
+Using multiple devices on *different* WiFi networks, while attempting to use ESP-Now, is likely impossible because the device's channel numbers will be modified to match the different channels of the Access Points.