Well, after many stops and starts, I have finally gotten a 160M inverted L
up on the island. I started with an inverted L for 40-80-160 using Unadilla
traps. The 40M section worked great but the 80 and 160 sections wouldn't
take more than 500W without breaking down. Rather than fool around with that
configuration, I took it down and tried something else on Saturday.
The new antenna is constructed from #16 insulated wire (1/4 wavelength). I
have mounted a 40 foot portable aluminum mast at the end of my dock, mounted
to a piling, 150 feet out into the salt water. The end of the L slopes
gently down to about 20 feet above the water at high tide and 27 feet above
the water at low tide. I have constructed a simple ground system by sinking
a 10 foot ground rod into the ocean floor under the dock. I have attached 4
125 foot radials to the ground rod which are spread out in the water. The
feedpoint of the antenna is attached to the ground system using heavy
tinned-copper braid. The radials and rod are covered with salt water all the
time.
The dock is about 15 feet above the ocean floor at its end. The floor gently
slopes into shore. The tide is about 6-7 feet difference from low to high.
After some testing on Saturday night and last night, I find the following:
The antenna transmits and receives VERY very well. Lots of EU, AF, SA and NA
worked with good reports.
At low water, the antenna SWR is 1:1 at 1830 (using an Amidon UnUn 50:12.5
ohms) and the antenna shows about 40 kHz of bandwidth (2:1 points). At high
tide the resonant point shifts up to 1860 (same feed system, same antenna
resistance, same bandwidth).
My question is: Do you think there would be less resonance change if the
horizontal portion of the L was really horizontal (I could probably get that
part of the antenna up to 35-40 feet, the mast/support end is probably 50
feet above the water at mid-tide. Please reply direct if you have any advice
or comments. Thanks 73 Steve AA4V
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