If you can use a heliax type of cable, you are looking at about 0.17 dB per
100 feet of loss (not counting the connectors), so 400 feet (300 + 80 +
shack end) will be about 0.7 dB, which will hardly be noticed.
Even the venerable RG8 foam will only be about 1.8 dB loss over that
distance, scarcely noticeable on transmit and zero effect on receive against
the normal terrestial noise background at 7 Mhz.
My concern would be with the rotator cable which may need beefing up,
depending on whether it is a DC or AC type of motor and its current/voltage
requirements to function correctly.
Good luck with the project.
TowerTalk mailing list