I need a single hole tube shape, that I can use up around 500 MHz. I've not found anything beyond 300MHz on Magnetics Inc, Fair-Rite etc. I need a cylinder shape with single central hole, OD <7mm, length non-critical.
I mention the shape because it's important in my application, and I've noticed a given material may only be available in certain shapes.
I remember seeing something like this used in UHF TV applications, probably in matching 300 ohm twinlead, and that would certainly cover the range I need.