Without a doubt, the most frequent question I get when I put anything on social media about CTR2-Mini or CTR2-Mini+ is What’s a CTR2-Mini?.

The short answer is “What do you want it to be?

This blog is dedicated to describing what CTR2-Mini+ is (“Mini+” for short), but I’ve realized (thanks to several commenters) that I really need one page, a “marketing page” if you will, that just tells you what a Mini is and why you might want one. So here goes…

In the beginning was CTR

The Mini+ is the forth generation of radio controllers that I’ve designed and built. CTR stands for Control The Radio. The Mini+ traces it’s linage back to the original CTR Windows Pocket PC program I wrote back in 2001. I designed a companion Bluetooth interface for CTR called CTR-BlueLync that allowed you to control your radio with your Pocket PC over a Bluetooth link. The project was published in the February 2007 issue of QST.

CTR and CTR-BlueLync

then came CTR2

Fast-forward 18 years when I decided I wanted a knob for my Flex 6400 transceiver. I had just retired and the pandemic was just starting so I had a lot of free time. I started working on CTR2, CTR‘s sibling on steroids. The “2” in CTR2 stands for “too” or “also” because in addition to radio control it evolved into a complete multi-radio station control system that didn’t just offer rig control but a contest memory keyer, DSP audio signal processing, FFT frequency display, CW and RTTY decoding, touchscreen with touch tuning, buttons, available Node-RED interface, and automatic rig and antenna routing. It quickly grew into an oversized shack control system that was very expensive and hard to build.

CTR2 Board Stack and CTR2 Touchscreen Console

QEX featured it in the Sept/Oct 2021 and Jan/Feb 2022 issues. I’ve kept the CTR2 blog posts here for posterity. They make excellent reading for chronic insomniacs 🙂

I discontinued work on CTR2 when global supply chain issues made it impossible to source the parts needed to build it. And honestly, because of the cost, there was very little interest in it anyway.

and CTR2-Mini

I started working on CTR2-Mini in Dec. 2021. The goal was to return to the original concept of a control knob for my Flex 6400 (and any of the other radio I own) by removing as much bloat from CTR2 as possible. This made it easier and cheaper to build.

I chose the Wio Terminal from Seeed Studios as the controller/display for this project. It’s a great little development system.

The Mini was featured in an article in the September 2022 issue of QST.

The original CTR2-Mini

and finally CTR2-Mini+

The Mini did almost everything I had envisioned but there were some compromises.

  • First, it was powered through the USB-C connector on the bottom of the Wio Terminal so you either plugged it into your PC or into a phone charger to use it. Powering from 12 VDC would be better.
  • Second, while it had a sidetone for CW practice and remote radio operation the volume was low and there was no volume control. More volume and a volume control would be nice.
  • Third, the Mini requires an external Radio I/O module to interface with any radio. While this is nice if you have more than one radio, it’s a nuisance if you only want to control one radio. A built-in radio I/O circuit would be handy.
  • Finally, new features have been added to the program that make the optional keypad on the Mini almost a necessity.

By the time the QST article on the Mini was published I was busy creating CTR2-Mini+.


Both the Mini and the Mini+ use the same firmware and operate the same. The Mini+ remedies the issues listed above. You can read more about the Mini+ here. The original Mini is still available on special order. Contact me if you’re interested in one.

So what does CTR2-Mini+ do?

I’m glad you asked!

CTR2-Mini+ and one radio

Radio Control

At its heart the Mini is a compact radio controller that you can put anywhere on your operating desk. It’s especially handy if your radio is not located directly in front of you. Now days it seems the keyboard and monitor get that sweet spot so I put Mini next to my key and keyboard.

The Mini interfaces to your radio’s serial CAT (Computer Aided Transceiver) port. For most radios built from the 1980’s to around 2015 the CAT port was a proprietary serial port using one of three standards, normal TTL levels, RS-232 levels, and the Icom CI-V two-wire bus. The Mini supports all of these standards.

The three major manufactures, Icom, Kenwood, and Yaesu developed their own CAT control protocols. Not to be out done, Yaesu modified their protocol for almost every new model. They finally settled on a modified version of the Kenwood protocol for their FTdx line (thank you!). Other manufactures adopted either the Icom or Kenwood protocols for their radios. The Mini supports most versions of the ‘big three’ protocols. It also supports the Icom PCR1000 wideband receiver.

Every manufacturer used a different jack or socket for their CAT port. The easiest to interface to is Icom’s CI-V, a mono 1/8″ phone jack. Arguably the worst is the Yaesu FT-8×7 models with that awful 8-pin mini-DIN connector. Such a tiny radio with such a LARGE CAT port! I can supply adapter cables that adapt the Mini to most radio CAT, PTT, and Key interfaces. I also provide links to them so you can buy them directly from the vendors directly. Some will required slight modifications, like replacing a mono plug with a stereo plug, or wiring a stereo jack to the accessory plug for your radio.

NOTE: Starting around 2015 manufactures started converting CAT ports from a serial port to a USB port. Most of the smart manufacturers continue to support the serial port in addition to USB, but some, I’m looking at you Icom and Xiegu, have chosen to go with only a USB port. At the current time the Mini doesn’t support USB CAT ports due to the insane complexity of creating a USB Host port to interface to a radio’s USB serial port. However, this is on my road map and I hope to have a solution sometime in the future.

One of the things you’ll really appreciate about tuning your radio with a Mini is the variable frequency step resolution. Press and hold the encoder then turn it left or right to increase or decrease the tuning step. Available steps include 1, 5, 10, 50, 100, 500, 1K, 5k, 10k, 50k, 100k, 500k, 1m, 5m, 10m, 50m, and 100m. Using these steps you can easily move around the band or the spectrum quickly. No more spinning the radio’s dial endlessly to move to another place in the band.

In addition, if the Zero Digits mode is enabled, the Mini automatically zeros the digits below the tuning digit allowing you to easily tune the exact frequency you want. With the tuning resolution set to 1k or below, the Mini automatically re-zeros the lower digits as you tune the radio dial.

Contest Keyer and Code Practice

As expected, the Mini also includes a keyer. But not just any keyer. The Mini’s keyer features classic Iambic-A and Iambic-B modes in addition to Ultimatic and Bug modes. A special mode called Passthru simply takes the Dit and Dah inputs from the paddle connected to the Mini and passes them through to the Key and PTT outputs on the Mini. This allows you to connect the PTT/Key Out jack on the Mini directly to your radios’ Key input with a 1/8″ stereo cable and use its keyer. The Mini automatically sets your radio’s keyer speed when you adjust the Mini’s keyer speed so you can use your radio’s keyer and control it with the Mini. You can also connect the Mini to an external keyer if you have one you really like.

The Mini also allows you to connect a straight key to it’s PTT/K Input jack and use it at the same time you’re using your paddles. On SSB the straight key can be used as a remote PTT switch if you prefer.

The keyer features 14 message buffers that can be assigned to function buttons on the unit. For contesters it allows you to assign your call sign, contact serial #, and contest exchange to prosigns (^, #, and %). This allows you to create a contest exchange in one of the message buffers. A special prosign, *, allows you to temporarily increase you sending speed 50%. This is useful for sending the customary 599 signal report during a contest exchange. Entering *599* into the buffer sends just the report faster. Buffer #1 is assigned as a repeat buffer. The last message sent is saved in this buffer. Assigning this buffer to a function key allows you to repeat a contest exchange with a single button press without incrementing the serial #.

The Mini also provides a keyboard keyer. Just connect the USB-C port on the Mini to your PC and connect a terminal program like Putty or Tera Term to the Mini’s virtual serial port. While in this mode just type then press [Enter] to key out your text. You can also control everything on the Mini with the keyboard meaning you can control your radio from your keyboard.

As we’ll see in a minute, the architecture of the Mini system allows you to share your paddles and its keyer with every radio in your shack.

A new code practice feature has been added to v1.09 firmware that provides a code practice generator for those wishing to learn or upgrade their code proficiency. The practice trainer is based on the Koch method of learning code. The minimum speed of the trainer is 15 wpm. This prevents you from learning code by visualizing the individual Dits and Dahs. You learn the code by how each character sounds. There are plenty of web pages that describe how to use this method so I won’t go it it here.

Remote Meter Panel

The Mini can also be used as a remote metering panel. Just select Meter Mode from the Mode menu and the display changes to display five meters, the S-meter, Tx Power Output, SWR, Compression, and ALC levels. This mode is ‘sticky’, i.e. it stays on once you enable it, even through power cycles. So you can just leave the Mini in this mode until you want to use it. Turning the encoder slightly will temporarily return to the Home page where you can tune your radio, change modes, or do other housekeeping tasks. After 10 seconds of inactivity the Mini reverts back to Meter mode. Press the [A] button (Esc) to exit Meter mode and return to normal operations.

The two screenshots below show the Meter page in receive mode on the left and transmit mode on the right.

External Tuner Mode

If you’re like many hams you have an external tuner because your radio’s built-in tuner just doesn’t cover a broad enough range. And, if you’re like most hams you probably cuss every time you have to change your mode setting and reduce power every time you need to peak up your tuner.

The Mini eliminates this frustration with it’s External Tuner Mode. When you enter this mode (from the Mode menu) the Mini automatically changes your radio’s mode to CW and reduces the output power to a setting you choose. In addition, the [B] button becomes a latching Key Out control. Just press it once to key the radio and press it again to unkey. If this weren’t enough, the PTT switch on the function keypad and a remote PTT switch become momentary Key Out controls. Just press any of these buttons to generate a tuning carrier. You can instantly change your output power by turning the encoder. When you’re done tuning just press the Esc button to return to the original mode and power settings. It couldn’t be easier! Here’s a photo of External Tuner Mode in active key out mode.

One Mini, Multiple Radios

As mentioned above, the Mini was designed to expand beyond controlling one radio. It can store radio profiles for up to 16 different radios. Use a simple manual RJ45 switch (or multiple RJ45 switches) to select which radio to operate. Each radio profile contains a favorite frequency list, CW message buffers, the CAT protocol, and other custom settings for that radio. You can use multiple profiles with the same radio if you have a lot of frequencies you need to remember, or CW message buffers for different contests or operations.

To select a radio just select the radio profile on the Mini, select the radio on the manual switch, and you’re controlling that radio. The diagram below shows an example of controlling four radios.

One Mini – 4 Radios

Third-Party Apps

About now you’re probably wondering if the Mini is compatible with third-party apps like log books and WSJT-X. Yes it is. Just plug the Mini into your PC and connect your third-party app to the USB serial port created for the Mini. Tell your program it’s talking to a Kenwood TS-2000. That’s it. The Mini will translate the Kenwood commands from the app to the protocol of whatever radio the Mini is connected to. You’ll still be able to control your radio using the Mini. If you switch to another radio your app won’t even know it.

This isn’t a full TS-2000 emulation, just frequency and mode, but that’s usually all the loggers and digital programs control anyway. If you’re running a full featured radio control app you’ll probably just want to stick with that.

Flex Control

As I mentioned previously, my primary driver for creating the Mini was to provide a physical tuning knob for my Flex 6400. The Mini uses WiFi and the Flex IP API to control your Flex over your network. It connects as either a GUI or non-GUI client. In addition, the Mini has enhanced Flex support that allows you to control many of the functions of the radio like Tx/Rx antennas, slice volume, bandwidth, filters, RF gain, Tx power, Tune power, and antenna tuner so you can operate your Flex in POR (Plain Old Radio) mode without SmartSDR running. The Mini even includes a ‘mini’ panadapter that’s available when the Mini is connected in GUI client mode. This panadapter, while not as robust and pretty as the SmartSDR panadapter gives you a sense of what’s happening on the band.

Radio settings can be assigned to the function keys allowing you instant access to the settings you change most. If that’s not enough, the Mini supports real CW and PTT over the network. Just take your Mini and a set of paddles with you and use SmartSDR on your iPad or connect your cell phone to an audio server like Mumble to handle the audio.

And yes, you can connect more than one Mini to your Flex at the same time. Assign each Mini to a different slice to get a physical knob and all the Flex features the Mini offers on each slice at the same time, including the link features described below.

If you’re just looking for a physical knob for your Flex without the keyer/sidetone and serial radio CAT features of the full Mini you can add just an encoder and a function keypad to a Wio Terminal. Visit the FlexRadio Features page for the schematic.

Enhanced mode for other radios

In addition to the Flex radios several other radio protocols provide additional control over the radio. The Mini currently offers enhanced support for Kenwood, Icom, and Yaesu FTdx models, including radios from other manufacturers that use these protocols. Like the Flex you can adjust many of the radio’s features from the Mini and assign them to the function buttons for instant access.

WiFi, Bluetooth, and Link Modes

The Mini supports both WiFi and Bluetooth connectivity to support several link modes. Link modes allow two Minis, connected to separate radios, to synchronize settings. In link mode one Mini is assigned as a server (Mini-A) and the other is assigned as a client (Mini-B).

Basic Link Mode

In Basic Link mode the Tx Enable mode and keyer settings are shared. This means that enabling the transmitter on one Mini automatically disables the transmitter on the other. Changing the keyer speed on one Mini changes it on the other. You can also push or pull the frequency and mode from one Mini/Radio to the other.

A special FTdx101 mode in Basic Link mode allows you to control the Sub receiver on the radio with Mini-B through the serial CAT connection to the radio on Mini-A. This allows two operators to use the radio at the same time. Of course only one can transmit at any given time. The Minis handle the transmit permission interlock automatically.

Basic + Frequency Link Mode

Basic+Freq link mode includes the Basic Link features plus the frequency and the mode of the two radios are synchronized. This allows you to use two separate radios on separate antennas as a full diversity receiver/transmitter. Just choose the receiver with the best signal when working a station that’s fading, or instantly start using the other transmitter if the main transmitter fails during a contest.

Basic + Tracking Link Mode

Similar to Basic+Freq link mode, Basic+Tracking link mode synchronizes the frequencies of the two Minis and their radios, but offset by their original (before sync mode was enabled) frequency spacing. For example, tune Mini-A to 14.1 MHz and Mini-B to 21.1 MHz then enable Basic+Tracking link mode. Now, tuning either Mini, or either radio will cause the other Mini and it’s radio to move the same distance. So if you tune Mini-A in this example to 14.15 MHz its radio will move to 14.15 MHz and Mini-B and its radio will move to 21.15 MHz. This is useful during a contest if you want to monitor the activity on two bands at the same time. To initiate a contact just enable the transmitter on the Mini you want to use and make the contact.

Remote Control Mode

In this mode Mini-B is in the shack, connected to your radio. Mini-A is the traveler. It connects to Mini-B over the network (local or Internet) and controls Mini-B remotely, just as if you were in the shack.

An example of linking for SO2R is shown in the diagram below.

Singe Operator Two Radio (SO2R) Control

And if that isn’t enough…

By now I hope you’re thinking, “Wow, that’s a lot of functionality in a small controller”. But there’s more.

The CTR2-Mini Antenna Switch Controller is a small controller also based on the Wio Terminal. It controls single and dual port remote antenna switches. It’s main advantage is that it can be linked to one or two Minis. This allows the switch controller to be placed out of the way and controlled by the Mini. You also have the option of having the antenna switch controller automatically switch antennas when you switch bands on the Mini.

Along with the antenna switch controller I’m working on an SO2R (Single Operator Two Radio) controller. The CTR2-SO2R Controller performs the functions shown in the diagram above. It allows you to use the radios you have to achieve full receiver diversity or SO2R operation. The SO2R controller isn’t quite ready for prime-time yet but if your interested in it, let me know.

A full-blown SO2R setup including the antenna switch controller is shown here.

Build it yourself

The Mini is designed such that anyone with moderate soldering skills can build the unit in a couple of hours. If you can solder .1″ pin headers to a PCB you probably won’t have any problem building the Mini+. To see what’s involved with building a Mini+ download the Mini+ assembly manual.

I can supply PCBs for either model. All PCBs have all the SMT devices preinstalled by the factory. You just need to add the through-hole components. I don’t sell complete part kits. Instead, you can purchase the components from my Mouser Mini+ Bill-of-Material page.

I can also supply fully assembled, programmed, and tested units and radio interface cables if you don’t want to build your own.

Is the Mini+ for you?

That’s a good question, and only one you can answer. If you’re strictly an FT8 operator, then the Mini doesn’t bring a lot to the table for you (but Meter mode might be useful). If you operate other modes the Mini has a lot to offer, most of which are described above.

At first glance the Mini might look like a solution looking for an answer. But if you think about it, doesn’t ham radio in this age of cell phones fit into this category?

If you’re the kind of operator that loves technology and is always looking for new ways to apply it maybe the Mini is for you. If you have multiple radios and would like a common user interface for all of them, maybe the Mini is for you. If your radios are more than an arm reach away from your operating position, or you don’t want to have to boot your PC and run SmartSDR just to check band conditions on your Flex radio, maybe the Mini is for you. If you’re like me, and you think it’s cool to be able to build a device that interfaces to some of the most advanced electronics in the world and actually adds to your operating enjoyment, the Mini is definitely for you!

Wrapping it up

I hope this answers the question, “What’s a CTR2-Mini?“. If you’re interested in seeing the user interface in action I have several YouTube videos on my channel (highly rated for insomniacs :). You can also download the CTR2-Mini Operation Manual for an in depth look at the user interface.

Is that it?

That about covers the Mini, as it is today. This is a constantly evolving project. As new options or modes are suggested by users, or just percolate up from my cerebral cortex, I add them. That’s part of the fun of being the developer… developing. I have several things on my road map including getting a USB Host port to work for USB CAT only radios. I’m sure other things will pop up too. The nice thing about the Wio Terminal is how easy it is to update the firmware. Just download the new firmware and copy it to the Wio. That’s it. No compiling, libraries, IDEs, or any of that stuff. Just copy and paste a file.

Thanks for checking out my projects. If you have any questions or comments please let me know. You can also contact me directly or via email. You can find my email address on QRZ.com.

73, Lynn, KU7Q