The major problem found in return sweep stability is generally cause by open outside sheet on the coaxial cable. We taught our tech. To use the proper tool to install cable, but some smart tech, still used a knife to remove the PCV.
And after time, with cold and hot weather it cause a crack on the outside of the coaxial cable which cause intermittent continuity between 5 and around 100 MHz. Once this found and repair the return signal usually stay stable.
We also installed a 75 ohms terminator on non used tap, it seem to help quite a bit.
We also have a + 15 dBmV flat input at all amp. and node and adjust the return using the UNITY GAIN technology.
Hope this help.
