Colorado’s First Derecho Wipes Out Two Antennas

A derecho (pronounced dare-h-o) is a strong wind not accompanied by a thunderstorm. Apparently they occur in the Midwest regularly but none had ever been recorded in Colorado before last week. One went through the state and took out two elements on the big 203BA 20 meter beam. It also folded over one of the 43 foot antennas. Reports were the wind was 87 mph.

Elements came loose from the reflector. Damage is limited to the small diameter tip tubing.
The reflector shouldn’t be so short. Good excuse to replace the single band antenna with a tri-band beam since the antenna has to come down for repair anyway.
The 43 foot vertical is on the right hand side of this security camera image. This is the second antenna damaged. Good excuse to replace it with a better quality antenna from DXEngineering. The other antennas survived.
A Cushcraft A3S tri-band beam with a 40 meter add on kit is being put together to replace the 203BA.
Assembly is completed and ready for swapping out when the tilt-over tower is lowered this week.

Things were going great when this picture was taken, except the elements seemed to sag a little more than expected. Once the tower was lowered and the new antenna was attached the sag became a real issue.

What was causing this? Opening a trap revealed a very loose screw. Upon trying to tighten the screw it became clear that it had been stripped out. Opening a second trap revealed the same thing. Searching the web and YouTube turned up many similar experiences. Each trap could be rebuilt with larger screws but there are 14 traps. That’s a lot of work just to be able to use a brand new beam. The antenna was returned as defective.
The dip was not where it should be which indicated something is wrong in the antenna–a loose connection or a short somewhere. Dimensions were verified. Loose screws in the traps are a good bet. Despite the terrible image quality the dip can be made out above the band where it should have been below when it’s on the ground. The frequency of the dip is at 14420 kHz.

A week later a New-Old-Stock Cushcraft A3S was found on eBay, made before the company was bought by MFJ, and it was purchased quickly. Assembling the genuine Cushcraft felt like better qualtiy from the get-go. What’s more the elements don’t sag nearly as much. Expected reliability is much higher with this replacement antenna.

The elements don’t sag!
Now the dip is where it should be when it’s still on the ground, about 200 kHz lower than it will be when up in the air. Much improved. Ready to be raised.

Up in the air now.

The dip sure didn’t move as much as expected, from 13.830 to 13.914 mHz. Two hundred kHz was expected, which would have put the dip at 14.030. Although the dip is outside of the band the SWR at 14.074 is quite respectable at 1.48. Next time the tower is down the antenna will be adjusted to move the dip up into the band. Meanwhile here’s a look at 15 and 10 meters.
Dip is way outside the band and the SWR at the FT8 frequency is 2.0. How bad is 2.0? It is mainly a concern to the transmitter which likes to see SWR below 2.0. How bad is it for effective radiated power?

dB = log10(1-x) where x is the loss in per centage. A rule of thumb for 2.0 SWR is 10 per cent loss. Therefore log10(1-.1) or log10(.9) is .45 dB. Loss of output from a 2.0 SWR is .45 dB. That’s a loss that can be lived with.

In testing the antenna many, many FT8 qso’s were made easily. This is the best performing 15 meter antenna at this station. (Yay!) Ten meters is not as rosy.

Dipping outside the band above the band is a surprise. SWR at the FT8 frequency is 2.65. The transceiver we are using begins to reduce output at 2.0 but does not totally shutdown until SWR reaches 3.0. Several FT8 qso’s were accomplished during the testing but probably would have been more if the dip was closer to 28.074 MHz. Using the transceiver’s internal tuner was not tried. Again, next time the tower is down for maintenance the antenna will be adjusted. It sure is pretty to look at. The 160 meter gamma match support poles can be seen on the side of the tower. They are the four white things sticking out.

Post script, 8/19/2020: A bad trap was found and repaired. One winding had shorted. Next, the A3S was modified to change the 20 meter band to 17 meters. It was then mounted on the small 30 ft. tower and works well. On the big 60 ft. tower the original Hygain 203BA was repaired and reinstalled. It works well, too, and all bands 20 through 10 now have a good yagi antenna. The A3S turned out to be more of an adventure than expected.

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