In tuning my InnovAntenna LFA 2-M yagis (and later my XPOL antennas) I needed a simple way to measure the Driven Element (DE) dimensions. The manual for my 2-M antennas says:
Hose clips are ready to place on the driven element sections and need to be loosened to allow the insertion of the end-loop element sections. The loop end sections are easy to identify and once inserted should be tightened to around 0.890m from the inside of the loop section one side, to the inside of the loop section on the other side. This loop will need adjusting once the antenna is complete with the above measurement being the starting point.
According to the manual for my 2-M antennas above, the DE loop sections should initially be set to around 0.890m from the inside of the loop section on one side, to the inside of the loop section on the other side. I found it really difficult to measure this distance across the square boom while I was trying to adjust them. So, I measured the width of the boom at 38mm and deducted that from the 890mm total distance (890 - 38 = 852mm). Dividing that by two gives 426mm from the inside of the DE to the closest side of the square boom.
The solution thus became obvious. Since the antenna boom is square, a tool could be built to measure from the closest side of the boom to the inside of the DE loop. So I took a short length of 1/2" X 1/2" wooden molding and taped a printout of a millimeter scale to it. The printout of the mm scale was not 100% accurate but I decided it would serve perfectly as a "relative" measuring tool. That is, if I measure one Driven Element at 426mm according to this tool, I could measure another to 426mm and they would be the same. It would not matter if the distance was actually 427mm. Just being able to adjust the corners of each DE loop to be the same distance and then adjust the DE loop on the other side of the boom to be the same was my goal. I positioned the printout on the wooden stick so that the "Ø" on the printout was exactly 300mm from the far end. That made it easy to adjust the DE's to the initial setting of 426mm (just add 300mm to the scale reading) and then move the DE's in easily repeatable amounts. (Click on any image to view a larger size.)
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| Custon-Made Driven Element Measuring Tool |
All I had to do was to place the end of the wooden stick on the side of the square boom and then measure to the inside of the DE using the scale on the measuring tool.
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| DE Measuring Tool in Use |
Once I tightened the hose clamp (Jubilee Clip in the U.K.) on one end of a DE, it was extremely easy to move the measuring tool to the other end, adjust it to the same measurement and then tighten that hose clamp. This made the adjustable portion of that DE square to the boom. Then I just used the same measurement on the tool to set the DE on the other side of the boom. Simple! I sure wish I had thought of this back in 2017 when I was trying to adjust my 13-L antennas!
And, after I posted the above, Carlos, WD6Y made a similar tool for 70cm:
