Failure again. This time it’s the fiberglass pole that has broken in half. Keeping a remote base running is a challenge. A guy rope had slipped from it’s anchor allowing the top to blow over. I am beginning to think using camo poles this high up is a hair brain scheme, especially after trying unsuccessfully to re-erect the pole today. This is what it looked like upon first approaching the site this morning.
Funny but performance had not diminished noticeably and this scene was a total surprise. In fact just this morning I worked a station in Cuba on the 20 meter inverted vee and thought all was well. Half of the vee is lying on the ground and the other half is running from the ground to the tip of the pole which is drooping down. Low band performance seemed to be normal, too. Go figure. Also keep in mind this has worked successfully for over two months without the need of a site visit, through snowstorms, numerous thunderstorms, and a week of 90 degree heat. No complaints.
Considering this antenna performed well when it was up I don’t want to change antenna design, only change the mechanical design. It needs to be stronger and easier to erect. Incidentally the purpose of the site visit had been to install a cable to make CAT work. That was successful and the remote now has CAT control.
Update 6/23/2016: A telescoping aluminum pole has been ordered as a replacement. It is a DX Engineering ATK65A kit. It is a 65′ kit of aluminum tubing. The plan was to erect it only 39 feet and connect the inverted vee as a top hat just as before. Then I remembered the modelling I did for a dipole which peaked at a height of 64 feet. A real possibility for success could be to install a dipole at the tip using two Jackite 16′ fiberglass poles and run coax down the inside of the new aluminum tubing. That design would match the model with the most gain at 15 degrees take off angle.
With lightning season in high swing lightning protection is an important topic. At the radio cabinet we are following the generally accepted practice of a single point ground system. This means we connect all devices to a single point so that at the moment of an “event” potentials will rise and fall simultaneously for all devices. Potential differences are eliminated and therefore damage is eliminated. For the single point we have chosen the ground rod at the equipment cabinet. An 8 foot ground rod has been driven and all devices in the cabinet are connected to it. Below, the ground rod can be seen as well as various wires connected to it making it the single point of ground. The frame of the solar panels is also connected to the ground rod. (Bonding the frame is not in compliance with NEC 2014. See “Section 690.47(D)” for details. We feel we might be ok here because we are not connected to the grid).
An appropriate surge protector is installed where each cable enters the cabinet and the protector is in turn connected to the ground rod. This is to provide a path to ground through the protector and not through the equipment.
The antennas are located 100 feet away from the cabinet (to solve interference issues ). If the two were closer the antennas and associated devices should be bonded to the same ground rod using 2″ copper strap. No. 6 copper ground wire would likely “fuse” and melt upon a direct hit. We could have driven a ground rod at the base of the antenna. If the antenna was closer to the equipment that would create a dreaded ground loop. At 100 feet separation it’s probably far enough not to hurt anything. The function of the ground rod is performed by the radial ground screen acting as an electrode.
Ward Silver, N0AX, says in an article in September, 2015 QST, Grounding and Bonding Systems, p69, “…if the tower is not located close to the house and it’s bonded earth connections..the radial ground screen can help spread out the charge.”
We’re going on the principal that we have two systems not bonded together except by the coax cables and the cable will “fuse” (and become an open circuit) upon a direct strike. We also expect the long cables will provide enough inductive reactance before they fuse to isolate the two systems. I believe NEC refers to this concept as “impedance” grounding. The two systems are defined as follows. One is the cabinet and a ground rod for a single point of ground. The other is the antenna and it’s radial screen acting as an electrode. There is no ground rod at the antenna. We expect the system that gets hit to dissipate 90 per cent of the charge. We expect the other system to suppress the other 10 per cent without damage. We further expect the cables in between to suppress a considerable portion of the charge before fusing.
Another important feature not to be overlooked is the shape of the antenna. A pointy vertical tends to put up feelers which lightning step leaders search for as they come down out of a cloud. A flat surface tends not to put up feelers. Our inverted vee flat top at the top of the vertical antenna provides that flat surface and reduces feelers.
Laughable inconsistencies. On the other hand the 20 meter EF-20 half wave vertical has everything wrong about lightning protection. It is pointy, likely putting up feelers during a thunderstorm. It has no ground rod nor ground screen. It is a culprit waiting to cause lightning problems. On the positive side it is a thin wire which will fuse quickly and it has only a coax running back to the equipment and it runs though a Polyphaser surge protector at the entrace to the equipment cabinet. Even though it’s a thin wire it can put up feelers and attract a lightning bolt. Once the EF-20 is vaporized the charge will need to find an alternate path to ground with an unhappy outcome. (I was checking the antenna one day as a thunderstorm approached, maybe 5 miles away. The coax was biting me something fierce. I hope those Polyphasers do their job.)
Another laughable inconsistency is the fact that the cabinet is not conductive. It is fiberglass. At the new remote base the cabinet will be made of stainless steel. Metal could prevent the charge from bypassing the protectors better than fiberglass. We just do the best we can given what we have.
A second remote base is under way. This is a de-commissioned tower from a business I once owned. The landowner called when the new company said they no longer needed the tower. My suggestion was to donate the tower for non commercial ham radio use and they went for it. I will pay the landowner reasonable fees to use his land and for electricity. Here’s what it currently looks like. That white road is pointing toward Europe. Nice, right?
The plan is minimalist. We will put a 20′ aluminum mast at the top of the 30′ tower providing a total height of 50′. At the tip will be a light weight dipole cut for 20 meters made from two 16′ Jackite fiberglass poles (http://www.jackite.com/product_info.php?cPath=41_44&products_id=98). A dipole at 50′ models very well and should have lots of gain for DX on top of a hill that slopes down toward Europe. Ground conductivity is good in the area, too. It should give us the productivity on the high bands we are lacking at the first remote base. In 2002 this was the very first tower for our wireless ISP. It’s had a lot of communications pass through it in it’s 14 years of commercial use. Now in retirement we hope it will see a lot of DX.