Serial port splitters are software utility programs that can turn one physical serial port into multiple virtual serial ports. When serial port splitters are being discussed, the first question asked is usually "why would I want to do that?". To answer that, you need to know that serial ports can generally only be used by one program at a time. Let's suppose that you use DxLab software for logging and rig control. All you had to do is just connect a computer to the radio to read the frequency, log it, and QSY the radio when you click on a spot from the Dx cluster.
OK, simple enough. But suppose you want to run another program at the same time and you want that program to also communicate with the radio. For example, you might want to enter a Dx contest and use a dedicated contest logger like N1MM and at the same time run DxLab in order to watch for new band countries. and QSY the radio to the spotted frequency. Or, you might want to run WSJT-X and a logging program at the same time. Well, now you have a problem. You shouldn't set two programs to use the same serial port, nor can you use a Y cable. If you do, both programs will try to communicate with the radio on that port and neither will work. What you need is a way to "split" the radio's serial port into two distinct ports so it can communicate with more than one program. You might even need a third serial port for an amp or antenna switch. Once you start automating the urge to expand tends is natural. Fortunately, it's very convenient to create a virtual serial port for each program you run that needs access to the serial port connected to the radio. Once a separate virtual port is assigned to each application you don't have to worry about which programs happen to be open before you open another. They could all be open and it wouldn't matter.
That is basically a description of my setup. I have used the Eltima Serial Port Splitter successfully for several years to split a physical serial port (Com3 in my case) into three virtual serial ports (Com8,9,10). Each of my dedicated programs is set to run on one of those virtual ports and all three programs can run simultaneously. You simply identify the physical port you want to split and create the virtual ports that your programs will use. Your computer and software applications treat these virtual ports as if they were physical ports. They even show up in Windows Device Manager.
20210416...Update!! I recently purchased an SDR radio. These radios generally do not have physical serial ports. Instead, they use a virtual serial port (on the ethernet connection) to communicate with software programs. That presents a problem for most serial port splitting utilities which can only split physical ports. That's the situation I ran into with Eltima. When I tried to split the radio's com port virtual com port the SDR's control program could no longer communicate with my logging program. Fortunately, I found a utility that can split not only physical ports but virtual ports, as well...Eterlogic VSPE (virtual serial port emulator). While this program requires a bit more geeking ability than some other solutions like Eltima, it is very flexible and powerful as well as very affordable at only $25 (try before you buy). Eterlogic is now my recommended solution, and is an essential utility for SDR owners who want to split ports. Eterlogic's VSPE allows up to 8 programs to utilize one virtual serial port.
Below are a few tips for getting VSPE to work:
+ Try before you buy
+ Set up one split pair and use the virtual port with up to 8 programs
+ Once it's working, set it up as a Windows Service so it will run automatically
+ Be sure to run Windows CMD as an administrator when establishing the Service