Update ESP-Now docs

Author: nseidle

docs/img/Radios/SparkFun RTK ESP-Now Distance Testing.png

@@ -1,5 +1,7 @@
 # Radios Menu
 
+## ESP-Now
+
 Surveyor: ![Feature Supported](img/GreenDot.png) / Express: ![Feature Supported](img/GreenDot.png) / Express Plus: ![Feature Supported](img/GreenDot.png) / Facet: ![Feature Supported](img/GreenDot.png) / Facet L-Band: ![Feature Supported](img/GreenDot.png)
 
 ![Radio menu showing ESP-Now](img/SparkFun%20RTK%20Radio%20Menu.png)
@@ -12,15 +14,23 @@ ESP-Now is a 2.4GHz protocol that is built into the internal ESP32 microcontroll
 
 Additionally, ESP-Now supports point to multipoint transmissions. This means a Base can transmit to multiple Rovers simultaneously.
 
-The downside to ESP-Now is limited range. You can expect your RTK device to be able to communicate approximately 1km (3200 ft) line of sight but any trees, buildings, or objects between the Base and Rover will degrade reception. 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 an external serial telemetry radio plugged into the **Radio**.
-
 The ESP-Now radio feature was added in firmware release v2.4. If the **Configure Radio** menu is not visible, consider upgrading your firmware.
 
+ESP-Now is a free radio included in every RTK product, and works well, but it has a few limitations: 
+
+1) Limited use with Bluetooth SPP. The ESP32 is capable of [simultaneously transmitting](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/coexist.html) ESP-Now and Bluetooth LE, but not classic Bluetooth SPP. Unfortunately SPP (Serial Port Profile) is the most common method for moving data between a GNSS receiver and the GIS software. Because of this, using ESP-Now while connecting to the RTK product using Bluetooth SPP is not stable. SparkFun RTK products support Bluetooth LE and ESP-Now works flawlessly with Bluetooth LE. There are a few GIS applications that support Bluetooth LE including SW Maps.
+
+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.
+
+![Max transmission range of about 250m](img/Radios/SparkFun%20RTK%20ESP-Now%20Distance%20Testing.png)
+
+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.
+
 ## Pairing
 
 ![Pairing Menu](img/Radios/SparkFun%20RTK%20Radio%20E-Pair.png)
 
-Pressing the Setup button (Express or Express Plus) or the Power button (Facet or Facet L-Band) will display the various submenus. Pausing on E-Pair will put the unit into ESP-Now pairing mode. If another RTK device is detected nearby in pairing mode, they will exchange MAC addresses and pair with each other. Multiple Rover units can be paired to a Base in the same fashion.
+Pressing the Setup button (Express or Express Plus) or the Power/Setup button (Facet or Facet L-Band) will display the various submenus. Pausing on E-Pair will put the unit into ESP-Now pairing mode. If another RTK device is detected nearby in pairing mode, they will exchange MAC addresses and pair with each other. Multiple Rover units can be paired to a Base in the same fashion.
 
 ![Serial Radio menu](img/SparkFun%20RTK%20Radio%20Menu.png)