Right to left so far: The red cable is a network cable to the Laptop used as a system GUI. The left SMA connection goes to the L10 GPS antenna. The center is the new external sma port that comes off the 8th (spare) splitter port and is used for an external radio. Anything that can receive RF can be used there. In this case I'm just going to use a little Yaesu VX8 set to "AM" mode on 50.485Mhz to listen for 50 Mhz Power Line noise. (this seems to be a good frequency for hearing it well). The right SMA connector is goes from the 8-port splitter to the main 25-1300Mhz Discone RX Antenna. Btw this is a new one I just got to replace the older one I use the last time I drove around. That older one was in a slightly sorry state. The newer one is a D-130J from Diamond Antenna.
Here's a pix that show the 8-port splitter I've been talking about internal to the Big Box you see above. It's the grayish box with marker noting -9db of loss. The top right most port is the one that is running to the new external SMA connector.
So this new external port can also be used with another RTL and something like GQRX which I've also tried to do. This works pretty good! However, the low-end Asus X551M laptop I'm using for this project about maxes out it's dual core cpu when I do this. I'd much prefer to use GQRX and an RTL than the Yaesu VX8 for listening/watching the band. However, this is a limitation of the laptop I'm using. I could probably run GQRX just fine with the Chrome Browser accessing the noise floor readings and doing the map visibility at the same time, but it looks like it takes the CPU right up to 100% and stays there pretty much. I don't want to compromise my GUI view by pegging the CPU with the grqx software, so for now I'll just use the little VX8 to listen to the AM audio as noted above. I'm sure it'll be fine, as this is what I've used in the past. The down side is that I don't have the spectrum display and waterfall that GQRX provides.
One day I'll get a fancier laptop, but this is the only real reason I would need it at this point so there's no real drive for me to upgrade the one I have.