After ordering the Acetal bar, (it may be delivered tomorrow) it was not fit weather wise for doing anything else so I went up into the attic to further the Moxon Antenna build. I thought I would knock a drawing up in Stanley style to show what the plan is.
This is the overall design, the front of the antenna is shown at the top. It is basically two half wavelength elements with their ends folded back. The driven element is the one that is directly connected to the transceiver by a feed line. The element at the back is the reflector and is the bit that captures the signal and reflects it to the front element on receive. On transmit, the outgoing signal is fed to the driven element and pushed forwards by the reflector. This arrangement gives the antenna forward gain and directivity. Forward gain also gives you an effective power increase on the outgoing signal. Not going to go into the depths of antenna theory but safe to say that this antenna will be directional and it will shove out more effective radiated power than what you put in.
The diagram also shows how I intend to create the driven element dipole centre.
The second diagram shows how the T connectors at the ends of the main spreader will be used to create the required spacing and the elements isolation from one another.
The hub is made from 15mm PVC barrier pipe and a number of equal T connectors, bushes for the T connectors and elements will be formed from Acetal bar, elements will be formed from 1/4" aluminium bar, components shown below.
Aluminium Bar
This is the 15mm barrier pipe.
and the JG Speedfit 15mm equal T connectors.
This is the main spreader that I have made so far for the hub. It is slightly oversize in length, I will adjust this to finished length when the elements are fabricated.
The centre connector will connect with another length of pipe to the T connector at the centre of the driven element. This arrangement of hub will create a mounting point for the antenna so that it can be fixed to a pole for portable use.
This shows the sizing relationship between the hub components and the elements.
This is making a start on the centre connector for the driven element. I need to gain entry to the centre of the connector to access the ends of each side of the driven element. I intend to file a flat on each bar end and then drill out to accept a pop rivet. The feeder cable will be prepared with crimped and soldered ring connectors on the centre conductor and shield of the cable. I should be able to get in with the end of the pop riveter and make the connections. Once verified as sound I will fill the opened up void with silicone sealant.
Hardest bit here will be cutting the horizontal, if I could get it out as a single piece I could refit it once the joints were made and the void filled with sealant, it would make quite a neat job. The injection moulded T connectors are quite robust, I used a tenon saw to make the vertical cuts. I'll put another picture up later with my success or failure with this.
Later.....
Success, I dug out my high speed rotary tool that I bought a few years back from a garage sale that we came across when driving back from holiday in Wales. I saw this in box of stuff that was on offer, it's about twice the size of a Dremmel and has a fully adjustable speed control, it came with a stand, an umbilical drive and a bunch of tools and collets, I think it cost me all of £5.00. I remembered it had some small rotary saw blades so I tooled it up and used it to follow the contour lines of the moulding, there was just enough room to get the blade in and cut a V at each side to join with the vertical cuts I had made before. It took a while to tease out the cut section but managed in the end with a combination of a very small screwdriver and a Stanley knife to finally separate it from the rest of the moulding, it came out in one piece anyway. I am suited with this but seeing how the internal construction is if I had to do another I would have just gone horizontal. The mouldings are very robust and the plastic is over 4mm thick at this point of the moulding. Pictures are done in artificial light and I must not have had the macro on for the second one but you should see that it should give me enough access.
Looking down from the top
I should not have a problem fitting the cut out back in once it is packed with silicone.
I am a bit vexed as I can't find my blowlamp at the moment, I don't think I took it to Jack's as I had no need for it in the kitchen build. It's in the house somewhere but hiding.