Thank you for your comments so far folks.

J Todd and Philo, putting the cable straight through the wall omitting the
two connectors is certainly worth me considering.

Rob, to answer your questions I will mainly be using frequencies up to
146MHz but with the hope of going into the low microwave bands in the
future. I will be able to put the connectors back to back so their centre
conductors can be soldered directly to each other. This would mean that the
connector bodies are about 10mm apart.

Thanks again,

JOHN