Standing the test of time...

A quick review of antenna durability for the late edition post today.  I thought this would be useful, because there are plenty of antenna designs out there, but very few that report back some years later, to say what is left of them!

Yesterday, during rather cold weather, I decided to do some maintenance on my 6m 2-element quad.  This was unashamedly based on this web site, way back in around 2012.  Since then, it's been a superb antenna for me - so much so that I have always resisted the temptation to buy an all-aluminium quad to replace it.

I immediately knew that making the antenna out of timber would not last very long in our windy, wet environment.  So I made a spider support from aluminium 90 degree pieces, and (eventually) the arms from spare fibreglass elements from a 7m fishing pole.

The good news is that, if you make the antenna as I did, plus a few minor alterations, then this will last you many years without trouble.  Mine is going into its seventh year now, still with the original components.  The feedpoint has had to be redone a few times, but only because I used TV 75Ohm coax with an aluminium outer for the 1/4 wave stub; this reduced to dust in our salty air in no time.  It now has an all-copper, heavy-duty coax stub.

Originally, for a short while, I recycled a Pfeiffer, 15m quad experimental frame in PVC tube to hold out circular wire loops for the 6m, 2-ele quad.  Of course, it worked very well, with maximum enclosed area.  One day, I hope I can try the linear-loaded Pfeiffer quad at 15m again, because, as you can see, the saving in size is quite considerable:

Early days of my 6m quad.

The trouble with the PVC is that is has a high wind loading area.  Worse, the glued 'tee' pieces very quickly deteriorate under UV light, to the point that they fail in about two years or so outdoors.  Despite this, you see an awful lot of US-based antenna designs using PVC tube.  My advice: avoid it completely!  And for intolerant neighbourhoods (my neighbours know to leave me alone!), that bright white plastic is not very stealthy!

I then made the quad look like this:

Second iteration.

Since this photo was taken in early 2013, the only change I've made is moving the coax down from the boom (which then stupidly ran down the lower driven element spreader again) so that it simply feeds directly the same lower corner (horizontal polarisation) from the mast itself.  This reduced the interaction between coax and antenna considerably, and reduced the length of feedline by nearly 3m.  You can see the arrangement in the last image of this post.

Here's the quad spider detail.  Tape and cable-ties were OK for those nearly 7 years, provided one changes the cable ties every two years or so, but the top arms slip through eventually.

What you  need to do - and what I was doing yesterday, it cut notches with a rotary tool in the 'L'-shaped aluminium, so that the cable tie (or, preferably, stainless steel hose clamps), make better contact with the fibreglass arm.  Typically, the arms are slightly smaller than the depth of the 'L' bed, so there is only slight contact between them and the securing fastener if you don't make notches.

Also, it's a good idea, especially for the topmost bracket, to drill a hole and fix a stainless steel bolt, to physically prevent the upper spider arm from slipping down.  You can do this for all arms if you like, as the tension of the antenna wire does tend to pull all of them inwards.

Also cover the exhaust clamps in plenty of grease to make them last longer.  In an ideal world, I would suggest you use stainless clamps for a square aluminium boom, not a round one.  This avoids slippage and rotation as one could get with round tube, though it has not been a problem for me.

When you think this antenna has gone through nearly 7 years of very strong sunlight and even stronger winds, then, for the peanuts it cost to build, it really is a true winner!

Serviced and ready for another several years.