[P8] A rethink.

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Struggling to overcome the angular difference between the feed boss and support arms blinded me to the obvious. Turn the problem on its side using small pieces of alloy angle to connect the components together. Problem solved. (Tomorrow)

Well, I solved the mismatched angle problem but introduced unwanted rotation. My use of square tubing (for supposedly extra stiffness over angle) offset the arms too much. When, ideally the arms want to be radial to the LNB/feedhorn.

Easily overcome by the use of metal angle instead of box section. Ensuring the arm clips overlie the boss fixing bolts will reduce offset to the absolute minimum.

Note that the feed boss is still reversed. When I tried it the correct way I'd need much longer arms to push the feedhorn out to the focal distance. I don't want to change the arm unnecessarily at this point. At least not until I settle on a practical way of holding the feed head perfectly still.

I still like the arm clips but need to reduce their ability to rotate around the arms. Any offset from radial greatly increases the torque on the clips due to imbalances.

I'm not sure the rubber boot on the LNB works. There is a bump on the LNB casting which might encourage rainwater entry. Self amalgamating tape is probably a better option but not until the design and tuning are complete.

Well, I've had to give up on the clips. They rotate on the arms too easily. I made some angle brackets, again using the clips, to make the arms radial. The head still flopped about.

Now I've flattened the brackets to the correct angle to match the arms to the boss. I'm using more expansion sleeves on the inner ends of the arms and bolting the boss direct to the brackets. It's a fiddle to get the focal distance to the feedhorn correct but I'm getting there. Finding enough screws and nuts is always a problem.  When it is finalized (famous last words) I'll use stainless steel fasteners.The image shows the latest iteration. Provided all the nuts are tightened with the head aligned it stays absolutely still. Focusing can take place by adjusting the nuts.

I have now removed one nut from each of the screws holding the boss. This achieved a better focus. The strong channel is back with the Satfinder shrieking right down to almost no gain on the control knob. This equated to 5 bars out of 8 for Signal and Quality on the satellite receiver.  

Click on any image for an enlargement.

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