Member - Lino VK3EI
Modifications to the EMDRC Club Mast

A portable mast is very useful thing for amateur radio use because we all know that “Height is might!”  Since joining the EMDRC early in 2009, I have purchased one 6m mast and three 9m masts from the club and I have another two on order.

During 2009, a number of us have made a few excursions to the Upper Yarra Reservoir to play radio and test out the various antenna constructions that we have concocted from time to time.  In the process we have come up with a number of modifications and additions for use with the club mast that have proven to be very useful indeed.

As necessity is the mother of invention, we were able to address a number of needs and come up with solutions which are very simple once you see them but are not always immediately obvious.

First, we found that we needed to raise and lower our antennas a number of times during our stay in the camping ground as we proceeded to try the different antenna configurations.  We solved this problem to some extent by mounting a pulley at the top of each mast and using it to raise and lower the antennas.  This is fine for wire antennas but does not help much when you want to try a yagi or some such antenna.

To solve this problem John VK3DQ happened to discover that the fiberglass poles that Roger VK3BKR had sourced for the club were a very nice fit over the top section of the club mast.  By cutting a piece about 1m long and slipping it over the top section of the mast and securing it with a bolt through the top section pin holes, he was able to clamp his yagi onto the fiberglass section.  This gave him the benefit of providing an insulated mounting for the boom of the yagi and also lifted it clear of the mast itself.  This arrangement is shown in Figure 1.

The remaining problem was the continual raising and lowering of the mast.  In my foraging around scrap metal yards, I came across some very nice aluminum castings which turned out to be ideal bases for the club mast.  A quick look around the plumbing section in Bunnings located some perfectly sized high-pressure PVC couplings which fitted the base section of the mast just nicely.  These couplings are mounted on a couple of galvanised angles and I have a nice pivoting base for the mast.  The finished base is shown in the Figure 2a and 2b and is easily anchored to the ground using tent pegs.  By measuring out the guy ropes and placing tent pegs at the appropriate locations, two of the guy ropes can attached and anchored and the third rope used to lift the antenna into its vertical position (don’t forget to tie off the third guy rope).

We found that with the base anchored, it is quite easy for one person to raise and lower the mast.

The red wire, visible in the picture, is bolted to the base and other end is connected to the mast using a hose clamp if you want to earth the mast, or left unattached if you want to have the mast floating (electrically), perhaps as part of an antenna.

For example, I have done just that in the 160m antenna that I made using the club’s 6m mast (see Figure 3) where the mast is the radiating element of the antenna.  The loading coil can be seen near the top of the mast.  This antenna is based on Drew’s VK3XU design of a 160m top loaded antenna.  The base for this antenna was of a slightly different construction (I didn’t have any more of the nice round castings) because it needed to have a feed point (SO259) and radials.  This base is shown in figure 4.  Note the wire that comes from the feed point connector and is hose clamped to the insulated mast.

Building on John’s VK3DQ idea of the fiberglass top section, I came up with a scheme for making a rotator for the 20m Moxon that I was building at the time.  I built the Moxon shown in Figure 5 using four squid poles as the corner supports for my wire sections. 

The poles were cable tied to a round aluminum disk of approximately 500mm diameter and the disk mounted via a hole in its center to the top of a section of fiberglass pole.  The fiberglass was then slipped over the top of the mast with the base of the fiberglass resting on one of the mast’s guy plates.  Note that the guy plate in mounted near the top of the mast where it stops from sliding down the mast by a bolt through the top hole of the mast.  With the guy plate resting on this bold, the fiberglass section has a nice smooth plate on which to rotate.  See Figure 6.

Finally I attached a rope to a hole drilled on the outer edge of the 500mm aluminum disk and used this to rotate the antenna into whatever direction I required – I then just tied the rope to the nearest tree to hold the antenna in the desired direction.

I hope that all this helps to highlight just how versatile the club mast can be and what great value it is. 

I am sure that many of you have also come up with innovative ideas and useful tips that could add further value to this great erection device.

73, Lino VK3EI