Metal enclosure not grounded is shield for HF?

Hi I enclose my HF transmitter inside a metal enclosure but I do not want to ground this enclosure for various reasons. Will this un-grounded enclosure still provide some shielding at HF, even if not grounded?

Not if the internal electric fields couple to the case non-uniformly. It must be uniform coupling of E & H fields to be shielded or shunted by an external low impedance like ground or shunted via an isolated RF transformer to ground .

However often the interface cables become the antenna for HF unless there are chokes used.

Then it's an unintentional radiator.

So is the metal enclosure of any good at HF if it is not grounded?
Apart from the radiating cables you mention.

Why can't you decouple the case - ground it to RF but not to DC/AC mains?
Frank

The transistor fin (collector) is insulated from the chassis using mica. However there are parasitic capacitance effects. That Is why I would like to use a floating potential enclosure (that will be used as a heatsink as well).