As you may, or may not know, I’ve been working on a Single Operator Two Radio (SO2R) option using CTR2-Minis and a new CTR2-Mini Antenna Switch Controller. I first introduced the concept in this post.

In this post I’ll go over the progress I’ve made over the past few weeks. In a nutshell, I received the new boards for the SO2R controller and the antenna switch and let’s just say they worked as designed. Unfortunately the v1.1 main board design needs to be tweaked again to eliminate a feedback loop that was causing instability when both Minis are off when the SO2R controller is turned on. A solution has been designed and tested for v1.2.

The lead photo shows the complete system deployed on my X5105 and FTdx101D. Please understand that I staged this photo to get everything into one photo. The Minis, radios, and antenna controller will be located in better locations once I’m fully operational.


SO2R Review

First, a quick look at the SO2R configuration drawing to help you visualize what I’m going to talk about in this post.

Two Minis are used to control two separate radios. Each Mini provides all its radio control features as if were all alone in the universe.

The SO2R controller in the center ties the Minis together and provides audio connections to and from the radios. The antenna port of each radio connects to a dual-port antenna switch that is under control of an the new CTR2-Mini Antenna Switch Controller. This switch allows any radio to be connected to any antenna but blocks connecting two radios to the same antenna (that would be bad).

The SO2R controller’s function is to route the common keys, PTT, microphone and headphone audio, and the function key pad to either Mini-A/Radio-A or Mini-B/Radio-B at the touch of a button. Audio from the selected radio is also routed to an external USB adapter which connects to your PC.

Both Minis and the antenna switch controller are linked to each other via WiFi.

SO2R Functional Diagram

v1.03 firmware brings Linking and Antenna Switch Control to CTR2-Mini

In order to support SO2R I needed the ability to link two Minis and their radios together so they operate as a single unit. The first requirement is that the Tx Enable on one Mini/Radio must be disabled when the transmitter on the other Mini/Radio is enabled. I also wanted to synchronize the frequencies of both radios depending on the Link mode selected. As described in the SO2R introduction post, SO2R options include basic interlocking, locking both radios on the same frequency, tracking frequency changes on separate bands on each radio, and operating one Mini as a remote to control the other Mini connected to a single radio. With the last three modes, changing the frequency on any radio or Mini changes the frequency on all of them. I also wanted the ability to remotely control the new CTR2-Mini Antenna Switch Controller so that either Mini could change the antenna routed to each radio or instantly swap the current antennas on each radio.

To accomplish these tasks, a new Link menu has been added to CTR2-Mini v1.03.xx firmware. This menu allows you to enable/disable linking, set the Mini to be Mini-A (the server) or Mini-B (the client), and select the linking mode (Basic, Basic+Freq, Basic+Tracking, or Remote). There are also options to set the IP address of the other Mini and the antenna switch controller, and fine-tune radio B’s frequency when synchronizing both radios to the same frequency.

When you deploy the CTR2-Mini Antenna Switch Controller and set it’s link address to Mini-A’s address, the Ant Sw menu appears on both Minis so you can control the functions of the antenna switch with either Mini or the switch controller. You also have the option of enabling automatic antenna switching based on the selected band. The antenna switch controller can be located away from the radios and the Minis controlling it.

The new CTR2-Mini v1.03 firmware can be downloaded here.

Here’s a coupe of screenshots that show how the new Link and Antenna Switch features are presented:

Mini-A Home Page

On Mini-A the 3 at the top-right indicates that this Mini is linked to the CTR2-Antenna Switch Controller and the #3 antenna is selected for Radio-A. Auto antenna selection based on band is enabled because the background of the Band label (20m in this example) is RED, the same color as the antenna indicator.

The At next to the antenna indicator tells us this Mini is assigned as Mini-A (the server) and it is in Basic+Tracking Link mode. The green antenna icon indicates we are connected using WiFi.

Mini-B Home Page

On Mini-B the 2 at the top-right indicates that this Mini also linked to the CTR2-Antenna Switch Controller (through Mini-A) and the #2 antenna is selected for Radio-B. Auto antenna selection based on band IS NOT enabled because the background color on the Band label (20m) is the default color, not YELLOW.

The Bt next to it indicates this Mini is assigned as Mini-B (the client) and it is in Basic+Tracking Link mode. Mini-B’s Link mode is automatically set by Mini-A. The green antenna icon indicates we are connected via WiFi.

CTR2-Mini Antenna Switch Controller Home Page

This is a screenshot of the Antenna Switch Controller. It uses the same notation as the Minis in the top-right corner when it is connected to WiFi. The 32 text indicates the A and B antenna port assignments and the green antenna icon indicates the switch is linked to the Minis via WiFi.

Oper indicates the switch is in Operate mode. It’s below the [A] button to indicate that this button controls this option. Press the [A] button to toggle the switch operate mode between Operate and Lock. In this mode no changes can be made to the switch.

Active indicates the switch is Active (antenna relays are selected). It’s below the [B] button to indicate that this button controls this option. Press the [B] button to toggle the switch between Active and Off mode. In Off mode the the antenna relays are deactivated and the two radio ports are open. In the Off mode all radio and antenna ports are displayed in grey.

Swap is the user selected function of the [C] button. Pressing the [C] button will swap the antenna on the two radio ports, i.e. antenna #2 will move to Radio-A and #3 will move to Radio-B. Press it again to swap them back. The user can select the function of the [C] button.

The main portion of the display graphically shows which antenna is connected to which radio port. You can change the name of the antennas to fit your antenna configuration. Click the encoder or the 5-way switch on the Wio and select the Port-A or Port-B menu to change the assigned antenna.

NOTE: The software on the Minis and the Antenna Switch, and the switch controller hardware are interlocked to prevent the same antenna from being connected to both radio ports on a dual-port switch.

The tag line at the bottom can be changed to anything you want, as long as it’s less than 26 characters 🙂


CTR2-Mini SO2R Controller

The CTR2-Mini SO2R Controller is a pretty simple device. There are no processors, therefore, no firmware. Just old school switches, buttons, a few latching relays, and a couple of op amps. Most of the complicated circuits are SMT devices so it will easy to have the board house do the SMT assembly. The only thing you’ll need to do is mount the through-hole components and assemble it.

The front panel is kind of unique. At least I’ve never seen one done this way before (but then, I don’t get out much!) It’s basically a single-sided circuit board. The front of the board has white silk screened control labels on a black solder mask. Pots and switches mount in holes cut in the the board by the board house. Each pot or switch has large solder pads next to it on the back side where each control’s leads are connected using short jumper wires. All the connections to the main board end up on two 12-pin headers that are jumpered to the main board using DuPont jumpers as shown in the next photo. Everything fits nicely in a PacTec KEU-7 sloped panel enclosure. The front panel replaces the aluminum panel supplied with the enclosure.

The front panel turned out so well that I wrote an article on the design process and sent it to ARRL to see if they were interested in publishing my method. I’m happy to report that they’ve accepted it for publication in QEX sometime towards the end of the year.

Inside the CTR2-Mini SO2R Controller

A closeup of the front panel in the next photo shows the various controls. They are grouped by function. Starting at the top-left, the Tx Enable buttons select the Mini and radio that will be enabled to transmit. (Both Minis and radios are active all the time but only one transmitter can be enabled.)

  • Pressing the A or B Enable button automatically enables Tx on the Mini connected to that port and disables Tx on the other Mini.
  • Pressing the [Tx Enable] button (button [A]) on either Mini automatically switches the SO2R controller to the enabled radio the same as pressing the Tx Enable button on the SO2R controller.
  • Paddles, microphone, and the Straight Key/remote PTT/function key pad signals are automatically routed to the selected Mini/Radio.

Below the Tx Enable buttons are the Tx Mic Gain pots. Each radio has it’s own mic gain adjustment. The power switch and the mic selector are below the Tx Mic Gain pots. Two microphone inputs are provided. Jumpers permit enabling mic bias and whether the Ring of the mic plug is used as PTT on each mic jack.

In the middle are the Rx volume pots with the Rx audio routing switches below them.The Rx audio switches give you four options:

  • Both ON (as shown in the photo): Rx-A audio routes to the left headphone speaker and Rx-B audio route to the right headphone speaker.
  • Rx-A ON, Rx-B OFF: Rx-A audio routes to both headphone speakers.
  • Rx-A OFF, Rx-B ON: Rx-B audio routes to both headphone speakers.
  • Rx-A OFF, Rx-B OFF: Rx-A and Rx-B are combined and route to both headphone speakers
    • This option allows you to listen to both receivers as if they were one. This is handy when using the Frequency or Tracking options in Link mode as described in this post.

The function buttons on the right side are programmable and can send CW buffers or open various menus on the Mini. The PTT button can be used to key the enabled transmitter. These buttons are routed to the Mini/Radio that has Tx enabled.

CTR2-Mini SO2R Controller Front Panel

One question you may have is “Do I need the SO2R controller to operate two Mini’s and two radios?”

No, you don’t! The controller simply provides a convenient method to control the signals to and from the selected Mini/radio. You can use the link modes with just two standalone Minis. The Minis manage Tx Enable switching and the antenna switch without the SO2R controller. You can use a mixer board to manage the audio. You’ll also need a way of routing your keys and PTT to the selected radio which can easily be done with a couple of DPDT toggle switches. I designed the SO2R controller to put all these functions in one box.


CTR2-Mini Antenna Switch Controller

The new CTR2-Mini Antenna Switch Controller (ASC) is a takeoff of the CTR2-Antenna Switch Controller. The major difference is that it is a standalone controller with it’s own display instead of an integrated controller as was done on CTR2. This means that you can use this controller by itself on almost any antenna switch on the market (that takes individual relay select inputs).

CTR2-Mini Antenna Switch Controller and 2×4 Antenna Switch

The new Antenna Switch Controller is shown above along with a custom switch I built from two cheap eBay 1×4 antenna switches. Yes, I got off a little on the CNC router when I cut the label on the switch face… it’s good enough for who it’s for 🙂

The new ASC has been designed to support 1×8 (1 radio port, 8 antennas), 2×4 (2 radio ports, 4 antennas) and 2×8 (2 radio ports, 8 antennas) switches. It can output +12V or Ground on the antenna relay select lines depending on how your remote antenna switch is configured.

It is specially designed to interface with the CTR2-Mini. When linked to a Mini, the Mini displays the switches’ settings and allows you to remotely control the unit. The screenshots in the Firmware section above show how the Minis and the ASC work with each other. Future plans are to create a simple Node-RED flow to allow you to manage the antenna switch controller over the Internet.

You don’t have a 2×4 or 2×8 remote antenna switch? No problem. Just buy two 1×4 or 1×8 switches and add coax jumpers to parallel each antenna input with those on the other switch (Antenna #1 on switch A to Antenna #1 on switch B, #2A to #2B, and so on). That’s how I created the switch shown in the photo.

For a 2×4 switch, use a DB9 breakout adapter cabled to the antenna switch controller board and wire pins 1 through 4 to A switch relays 1 through 4, and wire pins 5 to 8 to relays 1 through 4 on the B switch. Wire pin 9 (return) to both switches’ common input pins.

The antenna switch controller is expandable if you need a 2×8 switch. In this case buy two 1×8 switches and add an expansion board to the switch controller. On the controller’s expansion board wire it’s DB9’s pins 1 through 4 to relays 5 to 8 on switch A and and pins 5 to 8 to relays 5 to 8 on switch B. Again, wire pin 9 on the DB9 to the common on both switches.

You can also purchase a commercial 2×4 or 2×8 antenna switch. Just make sure it takes individual relay controls. If you plan to go this way, send me the link for the documentation on the switch you will be using so I can verify this switch controller will work with your switch.

A note about antenna switches

If you intend on using 2×4 or 2×8 antenna switches make sure that you use remote antenna switches with the highest port isolation you can afford. The offline receiver will be listening to the transmitted signal so the lower the leakage the better. My personal limit is +7 dBm (about 5 mW) of RF power on the offline receiver’s front-end. This means that if you are transmitting 100 watts (+50 dBm) on one antenna port there needs to be at least 43 dB of isolation from that port to the receiver on the unselected radio port. The cheap eBay antenna switches I bought have around 40 dB of isolation which works fine for me since I rarely use more than 50 watts. If you’re running 1 kW (+60 dBm) you’ll need at least 53 dB of isolation, but I would go for 60 to 70 dB to be on the safe side.

There are several lower cost antenna switches that you can build. KK1L has a 2×6 port antenna switch on his web site. It has around 60 dB of port isolation. The parts to build it are available at Mouser. The total cost is around $200 in 2020 dollars.

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