A 240V -12VDC Converter f air compressor?

Richard,
Depends on the type of compressor you have. My Thomas draws about 8A continuous, but many draw more. Any power supply must handle the startup current of the motor, and the extra current as the higher pressure is attained.
Having said that, the DC does not need to be filtered, and a hefty battery charger (>10A, possibly 20A) will probably not harm the motor, even tho they can put out over 17v unloaded.
If you have a 240/12v power supply for your HF radio, this should certainly run the compressor ok, as they can take up to 20A or so peak current.
It may be simpler if you have a spare 12v battery (doesn't need to be all that big) to run the compressor , but floated off a small battery charger.
rgds
Gerry

The power supply you need to run your compressor would be very expensive. Hundreds of dollars.

Why do you want to run the compressor on 240?

as others have said the cost of a decent Transformer to run the compressor could be prohibitive, on the other hand buying a jumpstarter pack could be handy, even one of the 900amp ones from supacheap auto makes a handy portable power supply for running lights, air compressor's etc. you will pick one up from $70-$100.00 that will start cars etc when needed. we have one here floating around all the time. handy as a pocket on a shirt!
you can then take the power to where it is needed!