As the subject of interference from adjacent masts has popped up again I thought that reviving this topic might be helpful. The filter I made allows a VX-7 with MFD to operate on Cyrn-y-brain; without it the receiver is completely swamped. I assume M6BWA used it when we did CyB; activation point was the fence corner above the carpark where the ground drops away very steeply.
The filter is not hard to make although I remade it twice, each time with heavier gauge wire as it did not remain stable as the coils distorted during rough handling.
Definitely worth having if you must use a 2m HH on RF saturated summits.
73,
Rod