diff --git a/exercise-book/src/nrf52-radio-puzzle.md b/exercise-book/src/nrf52-radio-puzzle.md
index b8730b6..9fdfe32 100644
--- a/exercise-book/src/nrf52-radio-puzzle.md
+++ b/exercise-book/src/nrf52-radio-puzzle.md
@@ -11,8 +11,6 @@ Your task in this section is to decrypt the [substitution cipher] encrypted *ASC
 
 ✅ Flash the `puzzle-fw` program on the Dongle. Follow the instructions from the "nRF52840 Dongle" section but flash the `puzzle-fw` program instead of the `loopback-fw` one -- don't forget to put the Dongle in bootloader mode (pressing the reset button) before invoking `nrfdfu`.
 
-> Note: If you experienced USB issues with `loopback-fw` you can use the older `puzzle-nousb*.hex` variants.
-
 Like in the previous sections the Dongle will listen for radio packets -- this time over *channel 25* -- while also logging messages over a USB/serial interface. It also prints a `.` periodically so you know it's still alive.
 
 ## Sending Messages and Receiving the Dongle's Responses
diff --git a/exercise-book/src/nrf52-troubleshoot-usb-dongle.md b/exercise-book/src/nrf52-troubleshoot-usb-dongle.md
index 6ef9303..9051ffe 100644
--- a/exercise-book/src/nrf52-troubleshoot-usb-dongle.md
+++ b/exercise-book/src/nrf52-troubleshoot-usb-dongle.md
@@ -32,20 +32,11 @@ Return to the ["Interference"] section.
 
 If you only get one line of output then your OS may be losing some serial data -- we have seen this behavior on some macOS machines. You will still be able to work through the exercises but will miss log data every now and then. Return to the ["Interference"] section.
 
-If you don't get *any* output from `cargo xtask serial-term` and/or the `cargo xtask change-channel` command fails then the Dongle's USB functionality is not working correctly.
-
-In this case you should flash one of the `loopback-nousb*` programs:
-
-Put the device in bootloader mode again. Now, run:
-
-```console
-nrfdfu nrf52-code/boards/dongle/loopback-nousb21  # you can pick 11, 16, 21 or 26
-```
-
-❗️ The number in the `loopback-nousb*` file name is the radio channel the Dongle will listen on. This means that when you program the Development Kit to send data to the Dongle, you need to ensure they are communicating on the same channel by setting
+If you don't get *any* output from `cargo xtask serial-term` and/or the `cargo xtask change-channel` command fails then the Dongle's USB functionality is not working correctly. In this case you should ask your trainer for a custom firmware which has a fixed radio channel allocated. This means that when you program the Development Kit to send data to the Dongle, you need to ensure they are communicating on the same channel by setting
 
 ```rust ignore
-/* make sure to pass the channel number of the loopback-nousb* program you picked */
+/// make sure to pass the channel number of the loopback-nousb* program you
+/// received from the trainer
 radio.set_channel(Channel::_21);
 ```