On 2/15/20, I pulled down the Cushcraft A-3S with A-743 40 meter kit for inspection. The resonant frequency of each trap was checked. Element lengths were changed slightly to move from the phone bands to the center of each band.
The table below shows the test result of each trap as checked with a Sark 110 antenna analyzer. The resonant frequency (Fo) was determined by looking for the zero-crossing of Xs.
|Trap Number||Type||Fo (MHz)||Description||Rs, Xs|
|1||TK||6.767440||New trap. Used on driven element due to close match with trap 2|
|2||TK||6.647285||Repaired trap. White insulator on hot side of trap had burned up. This is now used on the driven element since it matches trap 1.|
|3||TK||7.248060||This is a new trap that had replaced trap 2 when it burned up. Howver, the repaired trap 2 has been put back on the driven element since it matches trap 1.|
|4||TK||6.887595||This was an original TK that came with the A-743 40 meter kit. However, traps 1 and 2 match better, so they were used instead of traps 3 and 4.|
After reassembly, the antenna was mounted on the tripod near the bottom of the mast. VSWR sweeps were run from the coax input in the shack. 40 meters looks good. Other bands are tolerable. The minimum VSWR on 20 meter is 1.99 at 13.934 MHz. Other bands have a low VSWR, but it is not mid-band.
The antenna was moved to the top of the mast and swept again from the coax input in the shack. VSWR and frequencies are pretty much the same. There's an evaporative cooler below the mast, so tests were done with the antenna pointed a couple directions to see changes in VSWR.
|Pointed North||Pointed West|