I am installing a GPA-019 antenna to a GP-1850DF chartplotter/sonar. I bought this equipment used and the antenna cable came up about 6 feet short for my installation. It has been cut off before to about 18 feet. What kind of cable do I need to extend this? Also can anyone recommend a source for the splice of the old to new cable connection, as well as a new tnc connector for the back of the GP-1850DF? Thanks for your help.