Simple and efficient Top Loading for short 160 meter vertical..
Many radio hams avoid playing on 160 meters thinking that antennas require heaps of space...In fact this is not so....A 1/4 wavelength 160 meter vertical is around 130 feet tall and requires a minimum of 32 radials to make it work properly....Only a few of us lucky to have the space and the means to afford erecting and maintaining such a structure....
The following is a description of a short efficient 160 meter vertical....The pics show the secret to success..
The Top hat structure is 11 feet in diameter....The top hat was made using two old 14 inch Amperex aluminum film reel discs...Pics will show how I made a center hub and the attachment of the 6 spokes...I used 6 lengths of 1/2 inch aluminum tubing and slid 12mm tubing inside this for central strength, sandwiching these between the two flat discs and securing them with stainless steel bolts...Refer to the pictures....I ran a perimeter wire, 1/8 inch woven stainless cable, around the outer ends of the spokes...This assembly is light but very strong....
Beneath the Capacitance Hat assembly I installed a 70uh edge wound inductor from some old broadcast gear....This Top Hat assembly was then fitted to a 4 meter length of heavy walled 60mm aluminum tubing....Refer pics....I machined up a guy ring that fits just below the inductor and fitted 3 Debiglass guy lines....
This assembly was then fitted to a 40 foot triangular mast, and placed on an old 66kv electrical insulator cemented into the ground and secured with Debiglass guys ...This makes the Top loaded vertical 50 feet high insulated from ground....
At the base of the insulated vertical I installed an inductor made from 5/8 inch copper tubing 10 turns 6 inches diameter and 10 inches long...This inductor is used to fine tune the vertical to resonance and also for matching to 50ohms LDF 4/50 cable...
At the base of the vertical I installed a 2 foot diameter copper plate and attached about 40 radials in my case 150 feet long...
The end result turned out far beyond our expectations....The antenna is very high Q meaning that it is fairly narrow between the 2-1 swr points, maybe 10khz each side of resonance....Matching was easy, tapping the Heliax up from ground 2.5 turns to return a 50ohm match point zero reactance.. The antenna is installed at one of my farm properties and when I have to overnight I am able to play Topband....
A few notes about constructing this type of antenna....Firstly the measurements are not critical...This was put together with what was on hand..Versions of this can be built to suit small blocks....The secret of radials is to put down as many as you can...If you can only manage short radials every one will make a difference.....The main points are to make something that is reasonably efficient and able to withstand any weather ..Comparing this antenna to a 100 foot high inverted V it is 3 to 8db better on long haul DX work consistently...I have also made many comparisons against a 120 foot vertical and once more there is less than 1-2db between them..
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