I was thinking that 300 ohm twinlead is more sufficient than 52 ohm coax. The one problem with it is not getting it wet. If I were to wrap the twinlead in electrical tape, could it be possiable to combat that problem? I am living with my son. He said; " Dad, you can have an antenna, but it has to be 300 feet away and It has to be buried." How do you pump 100 MW without line loss at 300 feet? I was thinking of LMR-400 but at $1.00 a foot would break the bank. At 300 ft it is an ideal area for an antenna, ground radials and all.
[Edit to add] I assume, since you mentioned 100 mW you are referring to an AM transmitter. Post again if you are using FM.
Depending on the type of antenna you use you will have severe mismatch with the twin lead and lose most of your power in reflections back to the transmitter and in standing waves. Another consideration is that the twin lead is a balanced line and most likely your transmitter output and antenna input are not.
Water has a high dielectric constant (83 if memory serves) and electrical tape wrap will reduce the capacitive shunting effect of the water but not by much because the tape is thin.
It would make more sense, and avoid transmission line legal questions (see Part 15.219) to place the transmitter with the antenna and run power and audio to the transmitter with multi conductor cable. I used thermostat wire and buried it for a 40 foot run this way. It won't last forever but it is relatively cheap and can be replaced. Also, since the line would have low audio frequencies and not RF water on the outside will have no effect.
Neil
Thank you Neil, that did answer my question. I`ll try useing the 18 gage like you suggested. What I could do if legal is to use a baby monitor for the audio and just run the power wires.
What transmitter will you be using?
I am useing the i-AM variety talking house xmtr utelizeing the AM Band on the 1110 Frequency with an antenna hight of 20 feet The ground radials, (where I plan to place the xmtr) will be six sides, at a radius of 30 feet circumference. It rains here lately quite frequently so I know that the soil is rich and quite useful. My objective is aimed to the neighborhood anything that will account for a mile or more if possiable.