I was recently asked if CTR2 could select from a group of linear amplifiers in addition to radios and antennas.

The ham making the inquiry is thinking about replacing his W8ZR StationPro II station controller and was wondering if CTR2 could offer the same functionality. To be quite honest, I didn’t know anything about the StationPro II so I looked it up. It is a pretty impressive controller. It allows you to select between three radios, three linear amplifiers, and three antennas in any combination. It was discontinued back in 2017 but there are many of them in the wilds.

StationPro II uses two custom RF switches to route transceiver, amplifier, and antenna connections. These are electrically operated remote switches and are controlled by switches on the StationPro II front panel. The user wanted to know if CTR2 could interface to these switches.

The StationPro schematics are still online so I found the RF switches and came up with the configuration you see in the lead photo. The design requires both the StationPro Remote RF Switch and the Station Select Switch (if you want to select from multiple antennas) and mimics the features of the StationPro II.

In this configuration the CTR2 Radio Antenna Switch Controller (RASC) automatically selects one of three transceivers when the user selects a radio on the Radio Select page. The user then uses the Antenna Select page in the HMI to select the operating amplifier and antenna combination. This is done by setting the Antenna Mode switch to Multi to allow more than one antenna selection as shown in the Node-RED screenshot below. With the settings shown, the selected radio will be connected to AMP 3 and it will be connected to ANT 2 regardless of the band the selected radio is operating on. You can also select a band on the left and set a different combination of amps and antennas for each band.

Selecting antenna port #4 enables the amplifier bypass relay.

This is a very preliminary design. There are a couple of areas that need additional work.

First, the ALC and Amp PTT lines need to be routed from the selected radio to the selected amp. I’ve put together a preliminary board design for an external switch box to do this. The relays in the switch box will be driven by the RASC and ASC outputs and route the ALC and PTT signal between the selected radio and amp. The box will connect to the RASC and ASC outputs of the HMI with a CAT 5 cable. This cable will have an RJ45 breakout connector on the HMI end. The other end of the CAT5 cable plugs into the RJ45 jack in the center of the switch box. The signals from the three radios connect to a 10-connector pluggable terminal strip on the left of the switch box and the three amps will connect to a similar connector on the right side. The photo below is a Kicad 3D rendering of the design. The switch PCB is designed to fit into the same PacTec enclosure I use for the Radio I/O module.

Here’s the first draft of the schematic to help you visualize what’s going on in the switch box.

Second, and most importantly, there is no interlock on the Antenna Select page to keep you from destroying your amps! It is entirely possible to select all of the amps and the amp bypass at the same time. Key your transmitter and you just lost a lot of equipment.

Fixing this problem will be easy. I’ll just add another mode to the Antenna Mode switch on the Antenna Select page that allows one and only one port to be selected in ports 1 to 4. Ports 5 to 8 would still be allowed multiple selections to support multiple antennas in phased arrays.

This solution is not specific to just the W8ZR Remote RF Switches. You could easily replace these switches with other electrically operated three or four port antenna switches. The only requirement is that the switches need to be controllable using discrete hard wired connections (i.e. one wire to each relay with (+) or (-) common).

Since I don’t run linears at my QTH (I’m mostly QRP) the ham from the initial inquiry volunteered to help beta test this solution for me. If everything goes well this solution will join the list of CTR2 options.

If you’re interested in this project and want more information, contact me.

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