February 18, 2019

Cleaning the Verticals

 

Every once in awhile it is best to disassemble a saltwater vertical in order to clean and re-grease its mechanical junctions. This reduces Ohmic losses. The last time I did this, which was when the verticals were installed in the woods with an elevated counterpoise system, it dropped the reactive component at resonance down to 2 or 3 Ohms. I hope it happens this time. The tool kit assembled for this job is depicted below. 

W1ZY Vertical Radiator Ohmic Loss Reduction Kit for Suckers • $89.95 + Shipping

Dielectric grease, a copper scouring pad, a (red) mechanic's shop rag and a plummer's pipe brush are all that's needed to reduce Ohmic losses.

Total cost at Home Depot about $8.

 

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What I do is start at the top junction, where the tubing is smallest in diameter, and work my way down the vertical. Since I use set screws at the junctions, when I put them back together there is no alteration of the vertical's length. Once I separate two tubes at a junciton, I scour the outside of the smaller diameter tube with a copper pad laden with Brasso®, and then wipe off the residue with a mechanic's shop rag. I then use a plummer's bvrush, available at Home Depot, to burnish the inside of the larger diameter tube. I then lay dielectric grease on the outside of the smaller diameter tube and run it in and oout of the larger tube to distribute the grease throughout the junction. The tubes are then reconnected with hose clamps and stainless steel sheet metal screws which lock them tight. I then move down the vertical to the next junction. The whole process takes about 45 minutes for a 40 Meter 1/4 WL vertical made of 6' sections of telescoping aluminum tubing. Sometimes, if I feel anal compulsive, I will lay a bead of Liquid Electrical Tape around the junction ledge to further prevent water ingress, although this is certaily overkill. I do it mainly becuase I have the Liquid Electrical Tape available in The Shack.

Cleaning the Vertical Junctions

Junction seen after being disassembled, cleaned and refitted after application of dielectric grease. 

 

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I worked my way down the Southwest vertical in this fashion yesterday afternoon. I then reinstalled the contraption to the ground pipe, which is from a child's swingset. After resetting the two-tiers of three-point guys (1/8" parachute cord), I removed the Northeast vertical radiator from its feedline and used the MFJ Antenna Analyzer to sweep the Southwest vertical's feedpoint. Remember, both verticals have to be detatched from their feedlines in order to tune either of them individually. Check out the reading, provided below. 

 

Southwest Vertical Apparently Detuned 500 Khz After Element Cleaning

At least the reactive component is now down to zero. 

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False Alarm Evoked by Operator Error

Turns out I made a mistake. I overlooked the fact that one of the ends of a hose clamp was touching the Southwest vertical radiator, detuning it in effect. Once bent out of the way, the MFJ Antenna Analyzer readings presented a more reassuring 7.048 MHz resonance with a few Ohms of reactance. Interestingly, this is the same reading presented by the Northeast vertical a week earlier after resetting its ground radial system, as described in a previous update. So now both verticals resonate at 7.050, requiring each to be walked up in frequency about 50 KHz, which means shortening them by about 3". I will hold off doing this because tomorrow I am going to relocate the Southwest vertical even further into the Salt Marsh in order to more symmetrically distribute its ground radial system. 

 

Shortcuts for Builders

For those of you interested in ballpark shortcuts, below we find lengths and corresponding frequency deviations for 1/4 wavelength verticals on 7 MHz. Which means how far you have to adjust the vertical to walk it up or down the corresponding frequency.

• 6" per 100 KHz. 
• 3" per 50 KHz. 
• 1 1/2" per 25 KHz. 
• 3/4" per 12.5 KHz.