Tuesday, May 29, 2018

Fiberglass center support - 40M extended double Zepp

I do not recommend anything to anyone anymore.

Having said that, I am personally pleased with the fiberglass tubing products from Max-Gain Systems.

I wanted to replace the relatively short fiberglass over galvanized steel center support for my 40M extended double Zepp (edZ).  I had two goals:  make it higher and make it non-conductive - simplifying the routing of the ladder-line feed.  

The telescoping fiberglass mast from Max-Gain is very nicely made.  The clamps are well thought-out and the instructions are clear.  The problems I had were entirely my own.

The clamps are entirely non-conductive and have a clever over-center lever to hold the tubing in place.  My problem was similar to the old British motorcycle joke about fasteners in aluminum castings:

Stages of bolt tightening for the novice mechanic:
                                               Very Tight

I snapped one of the clamping bolts during extension of the third fiberglass tube - it had been tightened to the 5th stage above.  After that, I was much more cautious.

Within a month I discovered I was too cautious.  With the constant flexing in the wind, two of the sections had partially collapsed - you can see one just above the roof level in the image to the right.  The looped ladderline is a dead giveaway.  

My QTH is in an area with almost constant breezes (a good thing in the Texas hill country).  The mast has one clamping support (at the roof apex) and is guyed only by the 40M edZ itself.

This means the mast is free to move in the wind.  In strong winds (say around 45 mph), I have seen the top of the previous fiberglass mast bent to almost 45 degrees.  We have had wind gusts of over 65 mph during storms with no permanent damage - it waves around like a fishing rod.   But all this movement did allow the telescoping mast to creep downward, especially in the lower sections which bear the weight of the sections above plus the downward component of the tightened edZ wires. 

[I know I am taking a chance here with minimum guying - but I am willing to bear that risk.  The previous fiberglass support was up for well over 12 years with no
apparent damage.]

I did not want to secure the sections with non-conductive pins. Sooner or later I would have to lower the mast and Max-Gain specifically warns against damaging the tubing finish as clearances are tight.  The same argument applies for any sort of clamp that would mar the tubing.

What I devised is shown to the left, just above the clamp mechanism.  It consists simply of three or four layers of electrical tape overlaid with a very tight tie-wrap (I have lots of tie-wraps, so I don't mind snapping one to get to stage 4, above).  Obviously I had noted that the tubing collapse halted when the electrical tape and tie-wrap holding the ladderline hit the clamp.  

Seems to work well.  I will post a follow-up report in a year or so.   

40M extended double Zepp details:

Orientation:                Roughly North-South
Center height:            about 46 feet
South end height:      about 25 feet (Live oak)
North end height:      about 30 feet (Pine)
Feed:                          450 Ohm ladder line

Best wishes to all.

cln - Nick

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