The Marconi Receivers 394E and 394F were fitted in very small craft e.g., ML's, MTB's etc and in some minor W/T shore stations. They were fitted in association with the Marconi Transmitter TW12.  So, for some of its information,  have a look at the Transmitter Matrix to Transmitter TW12 scuttle.

The 'E' version had a frequency range of 150 - 3000 kc/s and the 'F' version. 150 - 4200 kc/s. 

This small file tells one about the next size up {!} namely a few notes on the 'G' version {with a mention of the 'F' version} which is very similar to the versions already mentioned  RECEIVER 394F and G.pdf.