Here's a quick line loss calculator to use Note that the simple program used for this web page gives a very close approximation for additional losses due to SWR.
Coax Cable Loss / Antenna Gain Calculator
This program is provided "as-is". It is thought to be accurate but it is the responsibility of the user to verify the accuracy of the calculations when using this program.
INTRODUCTION-The longwire antenna is a very effective antenna for the
listener who wants to cover all of the shortwave bands from 530 KHZ to 30
MHZ. However if you have some favourite frequencies that you listen to on
a regular basis you may wish to consider a dipole antenna. This antenna is
a fairly easy to construct antenna and will give you better reception on
the frequency it is cut for. Think of a dipole as a longwire that has a
insulator in the middle.
234 / design frequency in MHz = each dipole side length in feet.
468 / design frequency in MHz = total length in feet.
Most builders cut long and trim the total
length for lowest swr on their design frequency.