SmartSDR USB Passthrough available in SSDR 3.9

Mike-VA3MW

I am getting this out early, as SSDR 3.9 should be released in the next week or so. Here is one of the features that I find very useful (writing this on May 24th, 2025).

SmartSDR Serial Passthrough

With SmartSDR v3.9 and above, FlexRadio introduces Serial Passthrough, a handy feature that lets you connect and control RS-232 serial devices—like antenna rotators or amplifiers—directly through your radio over the internet using SmartLink. 

Whether you're running third-party software like PSTRotator or other Windows-based control apps, this guide walks you through setting up your FTDI RS232-USB cable, configuring SmartSDR, and getting everything talking seamlessly.  

The hardware you are controlling must have an RS-232 connection.  

Devices that use proprietary USB protocols (e.g. NOT serial/RS-232) will not be able to connect.

How to Configure Serial Passthrough in SmartSDR

Step 1: Connect the FTDI RS232-USB Cable

• Plug your FTDI USB-to-RS232 cable (the one connected to your external device like a rotor controller or amp) into one of the USB ports on your FlexRadio.  These cables are available from the FlexRadio store.

Step 2: Set Up the Cable in SmartSDR for Windows

1. Open SmartSDR for Windows.  SmartSDR must be v3.9 or greater.
2. Go to Settings > USB Cables.
3. Find your USB cable in the list (look for its serial number).
4. Click Edit, then set the Type to Passthrough.
5. Double Click on the Cable to Edit the setting
6. Click on Advanced
7. Set the Baud rate of the device.
   

Click OK or Apply to save the changes.

Step 3: Create a Passthrough Port in SmartSDR CAT

1. Launch SmartSDR CAT.
   

Click to Create a New Port, and choose Passthrough in the protocol selection.

3. Select the same USB cable from Step 2 (matched by serial number).

Step 4: Use the Passthrough Port in Your Application

• In your third-party app (like PSTRotator or another device control program), choose the COM port that was just created in Step 3.
  
  • You can find the COM port name in SmartSDR CAT.
    
• Make sure your application is set to use that port for communication.
  

📝 Tip: Double-check in SmartSDR CAT that the Process is showing the name of the application you're using (like PSTRotator, PuTTY, etc.), which confirms the connection is active.

Gord-VA7GP

Excellent!

Currently, I have a local-to-my-Flex computer, and when I'm away-from-home I use Remote Desktop to connect to this local-to-my-Flex computer and spin my rotator. This pass-through feature could be very handy for a few such serial add-ons.

VK2NTK

Is this feature likely to work with the ACOM 1200S? Will I be able to turn the AMP on an off remotely and one more, Will the Mac version of SmartSDR work? I assume Marcus will answer this one. Thanks and 73's Jack

K1UO Larry

Hmmmm,, Might be able to rid myself of the 2 port l NPort serial server that now controls my Ultrabeam dipole and the RT21 rotor controller through PSTRotor-AZ. Not sure if I will lose some of the other controls through the PSTRotorApp like controlling the 8 port WEB KMTronics switch to allow remote on/off of Flex plus remote PTT.

Howard K7JNX

To use this completely I'd need 3 USB ports on my 6600 which only has two. Can one safely assume that it would still work if one used a USB hub?

WX7Y

Yes be sure you use a good quality POWERED Switch and Flex recommends it have a metal case, Mike talked a little on this in the video.

Asher - K0AU

Finally! Serial passthrough has been requested since the first SmartLink release. I searched the forum and Ken asked for it in 2019.

Anything else planned from the feature request backlog? In my tech companies we always had a roadmap we shared with customers even if features weren't scheduled yet. Aurora sounds like a cool idea, but many of us were hoping for more software investment in the existing 6K/8K platforms.

My priorities would be: multi radio support in SSDR and an AI roadmap. I'd love to see the WPF dependencies removed from Flexlib because that would promote more 3rd party software. A software connector for shipping VITA streams to the cloud and an orchestrator to manage radios at different sites would be interesting. A 3rd party program for the on-radio DSP could get us some things like native FT8.

In the same way that Aurora simplifies hardware integration, I'd like to see simpler software. To operate FT8 I have SSDR, DAX, CAT, WSJT, JTAlert, DXKeeper with several apps, often PSKReporter. In many ways SSDR, DAX and CAT are the least interesting parts of the stack and if FT8 is integrated all that's left is logbook integration. At the minimum an SSDR "FT8" mode that shrinks the pan to a mini box (and ideally shows FT8 on adjacent bands) and then has transmitter status is all we need.

If this is the wrong thread to discuss features we'd like to see on the roadmap, then move this to a feature request thread.