If you have to bury the feedline, I'd ditch what you have even if it
is not all contaminated or oxidized and replace it with a run of 1/2
inch LDF4-50 heliax. It is really not much more expensive if you get
it from Davis RF--they have very competitive prices--and it will be
years as in decades, before you'll have to deal with this problem
again. Also, do not fall into the trap of thinking a certain sort of
feedline is okay because you will only be using it to carry low band
RF. A run of RG213 of only 100 feet can provide a surprising amount
of loss on 1.8 MHz to a matched load--the best possible
conditions--and a dB here and there and it starts to add up. It is
expecially important if you run relatively low power. QRP operators
have the most to lose. A common mistake is to think that for QRP, RG
58 is okay, basing that on the power handling rating of the feedline
instead of loss. QRP operators should have the best possible
feedline. But that is off the topic as you may not be running
extremely low power. Still, if you go to one of these on-line loss
calculators and enter some data about common coax types on low
frequencies to a matched load and average lengths you may be surprised
at the loss.
73
Rob
K5UJ
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