I'm not sure I understand how the radar signal is supposed to work. I've tried adding a filter to the modified "combinator", connecting it with and without a radar connected via the circuit network to a power pole, and the only output on the power pole is from the combinator itself. I've waited more than 4 seconds and the "detected" items never updates, just outputs whatever signal the combinator is giving. I tried setting the constant integer to 0, but no signal is ever given.

Even in the picture given in the information tab, it looks like the combinator is coded to have a constant value of 3 for the solar panel signal which is then sent to the power pole.

Am I missing part of the setup?

Start with a radar and place the special combinator exactly next to the radar. Then put any filter and the amount should update based on the entities that are found in the vision range of the radar.
Connect the combinator to the network as with a regular one.
If the radar is not working then the signals also not updating. And you can only check for things that can be placed down or units

I fixed an issue that prevented multiple combinators to be updated. Only the first combinator was properly updated so my testing always worked...
I assume your problem occured when you used multiple of these combinators around the map. This should now be fixed.