This chapter covers everything related to the configuration, setup, and optimization of Wi-Fi.

Basics

Getting started with CTC modules and their Wi-Fi often proves to be a major hurdle. For this reason, we begin here with a few basics.

Fundamentally, CTC uses the standard functionality of Wi-Fi. The term WLAN is only commonly used in German and is too generic — the standard in use is called “WiFi”. Our CTC router is also just a standard Fritz!Box on which we perform a few basic setup steps for you (see the “Router Configuration” section below).

A typical Wi-Fi network always has a name (SSID) and should have encryption (password) to prevent unauthorized access. Encryption standards include WPA, WPA2, and WPA3.

  • WPA is largely ineffective, as it can be cracked with minimal effort using freely available tools.
  • WPA2 can also be cracked, but with significantly more effort. For most devices (including CTC modules), this is the highest level of security supported.
  • If only WPA3 is enabled, the CTC module cannot connect to the Wi-Fi network.
  • You should therefore set your model railway Wi-Fi to “WPA2” or “WPA2 + WPA3”.

In addition to the non-unique SSID, there is also a MAC address for the Wi-Fi network. This is globally unique but is typically only used at a technical level and often not displayed to the user.

A Wi-Fi access point is a device that provides wireless (Wi-Fi) access to a network without offering additional networking functions. A Wi-Fi router, on the other hand, includes the full functionality of a network hub and usually also provides internet access. For CTC, it is important that the Wi-Fi router, using the DHCP function, assigns the IP addresses required for communication. The smallest variant of a Wi-Fi router is a hotspot from a mobile phone.

There can be any number of Wi-Fi networks with the same SSID. This is used, for example, in so-called mesh networks to make Wi-Fi available over a larger area using multiple Wi-Fi access points (and a Wi-Fi router). However, all these Wi-Fi access points must be connected to the associated Wi-Fi router. These Wi-Fi access points are also called “Wi-Fi repeaters”. If the CTC module detects multiple Wi-Fi networks with the same SSID, it is difficult to predict which one it will connect to.

A CTC module supports two operating modes for Wi-Fi:

  • In configuration mode, the CTC module creates its own Wi-Fi network, acting like a mini-router. In this mode, the module can only receive configurations—specifically, the SSID and password of the model railway Wi-Fi. The CTC module’s Wi-Fi network has an SSID but no password, meaning it is unencrypted.
  • In normal operation, the CTC module knows an SSID and its associated password and attempts to connect to the Wi-Fi network with this SSID upon startup.

Wi-Fi Mesh

As of firmware version 20250627 (CTC app 4.40), CTC modules also work reliably in a mesh network. The following should be noted:

  • From CTC’s perspective, a mesh exists when there is more than one access point with the same SSID, all connected to a shared router.
  • On startup, the CTC module connects to the first available access point with a matching SSID. The search typically begins with the Wi-Fi channel last used for a connection.
  • The CTC module remembers the Wi-Fi channel used to connect to the model railway Wi-Fi. If the Wi-Fi signal becomes too weak, the CTC module automatically searches for alternatives (routers with the same SSID), but only on the same Wi-Fi channel. Only after 60 seconds without a Wi-Fi connection does the CTC module search across all Wi-Fi channels again.
  • The search on the same Wi-Fi channel takes approximately 300 ms. During this time, the CTC module is unreachable.
  • The minimum signal strength considered “too weak” can be adjusted in the Wi-Fi configuration (“Signal min. db”) of the CTC module.
  • The Wi-Fi Monitor not only displays the signal strength history but also the currently used access point.

Wi-Fi Icon

Since the reception quality of the Wi-Fi signal has a significant impact on CTC, it is displayed in various locations using the following symbols:

Symbol Meaning
ctc-app-doku-icon Optimal Wi-Fi reception (> -67 dB)
ctc-app-doku-icon Good Wi-Fi reception (> -70 dB)
ctc-app-doku-icon Acceptable Wi-Fi reception (> -80 dB)
ctc-app-doku-icon Poor Wi-Fi reception (≤ -80 dB)
ctc-app-doku-icon CTC module with old firmware that does not yet transmit signal strength.
ctc-app-doku-icon CTC module has not reported for at least 3 seconds.
ctc-app-doku-icon CTC module has not reported for over 10 seconds.

The last two symbols (yellow and red) do not indicate the reception quality of the CTC module. It is possible that the CTC module is still well connected to the Wi-Fi, while the CTC app has lost its connection to the Wi-Fi. This is particularly likely if all CTC modules switch to yellow or red.

Router Configuration

In this section, we collect documents for configuring routers:

Tips for Wi-Fi Connection

Both laptops and smartphones and tablets have an ever-increasing urge to connect to the internet. This leads to them being reluctant to connect to Wi-Fi networks without internet access and often spontaneously disconnecting from them. CTC does not require internet access, which is why the model railway Wi-Fi is often set up without an internet connection.

The challenge is to ensure that the devices running the CTC app connect to the model railway Wi-Fi and do not spontaneously disconnect from it. Here are a few tips:

  • Connect PCs and laptops that do not need to be moved during model railway operation via an Ethernet cable.
  • Disable the “auto-connect” option for all Wi-Fi networks or enable it only for the model railway Wi-Fi.
  • Switch the smartphone to airplane mode and then enable only the Wi-Fi.
  • If issues arise, check whether the PC or mobile device is still connected to the correct Wi-Fi.

Tips for Optimizing Wi-Fi Reception Quality

  • Laptops or PCs that are not moved should be connected to the Wi-Fi router via an Ethernet (LAN) cable. Often, reception issues have shown that the laptop—not the CTC module—was the cause.
  • Use the 5 GHz Wi-Fi band for the device where the CTC app is installed. This forces communication via the Wi-Fi router, which often has a significantly better position for communicating with the CTC modules.
  • For smartphones/tablets, there are so-called Wi-Fi analyzer apps, such as the ad-free “WiFi Analyzer (open-source)” for Android. With these, you can move to different locations on your model railway layout and check how strong the reception of your model railway Wi-Fi is and how many competing Wi-Fi networks are present. If necessary, it may be worth changing the channel of your model railway Wi-Fi.
  • Using the Wi-Fi Monitor, you can display the signal strength of locomotives more precisely and over time. The displayed graph can help you find the optimal position for your Wi-Fi router.