[P6] Feed boss angle problem!

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The angles on the new boss are obviously designed for through-the-dish support arms. See the image where the new arms are fixed at the rim brackets. (Just like the originals) I used handy wall plugs just to prop the inner ends of the arms in place.

The difference in the angle where the arms meet the new boss is so large that I cannot just make the holes larger and crank down on the nuts. I need to keep the boss perfectly flat so that the skew ring and feedhorn lie perfectly flat and true to the dish. So trying to bend the boss will guarantee it all ends in tears.

I think the only simple way around the problem is to make small brackets. These will match the angles at the cost of greater complexity and some cosmetic untidiness.

Though I could bend the arms the aerial tubing is seam welded and not particularly tough material. Bending the arms would be a finicky job trying ensure the boss ended up at exactly the correct height and perfectly square to the dish. Nor do I presently own a pipe bender and the cheapest tend to distort the tube.

Or I could drill holes in the dish and make shorter arms held by dish-penetrating screws, load spreading washers and expansion plugs.

Problem solved! I just found a 12mm plastic pipe clamp which will hold the arms very firmly. While still allowing sliding motion for focusing. It just required the feed boss to be inverted. The feedhorn and clamping [skew] ring fit just as well as before. There was no room for the arms to go under the ears but they easily fit on top instead. I just need to obtain two more clips from somewhere. I can no longer remember where this clip came from.  

My first attempt to use the white plastic clips with inverted boss proved to lack clearance for the feedhorn. The clip has to go on top of the boss.

Then I found some simple metal clamps to fix the feed temporarily to the arms but ran into all sorts of other problems.

The mounting was intended for 80mm pipe and my existing pole was only 70mm. So I turned a brass cap for the pole to locate the top within the 80mm  socket and to stop it moving. Then I discovered one of the threads on a welded-on pole clamping nuts was stripped. So I couldn't clamp the mounting firmly to the pole even with the pinch bolts fully screwed in.

Getting the dish up on top of the existing pole was a real struggle. In the end my wife had to help me walk the dish and mounting up a ladder until it could be dropped over the pole. The pole was far too tall for the prime focus dish and the dish itself looks absolutely vast from the end of the drive.

I quickly obtained one strong channel on the satellite but could not get anything from the weaker ones. The strip metal arm clips I used were far too flexible and the feedhorn was too far from the dish. So I brought my checking spacer tube into play to reset the feedhorn to the correct focal distance. I shall just have to find more of the strong plastic clips to ensure stability of the head once adjusted.

Then the top security nut on the elevation screw proved to jam on the bracket to dish fixing screw heads. So I had to dismantle the entire elevation screw and turn the nut to half the thickness in the lathe and then dome it to ensure clearance at all angles of elevation.

After all these issue were resolved I had moved the dish well off target and could not get the strong channel back despite the Satfinder meter screaming its head off.  I have a tiny 4" B&W CRT TV which I used as a monitor for the satellite receiver alongside in the garden. A larger, colour monitor would be a vast improvement for reading signal quality bars but I have nothing suitable for outdoor use.

I was convinced I had the correct satellite but it wasn't. I checked Satpointer again on the computer and found a distant building to align on. As soon as I turned the dish that way the strong channel was back. Still nothing from the weaker channels. A long, tiring and frustrating day with little real progress to show for it. Though I did get the dish mounted and a signal from it.

I learned today that the Satfinder meter doesn't care which channel is selected on the receiver. It will scream on every satellite it finds. It also makes a different tone on each transponder.

I also learned that I should take nothing for granted until proven correct. I wasted at least an hour searching for a signal on the wrong satellite. With the mounting flopping about on the pole I was constantly losing my elevation setting as well as azimuth. Today was still, overcast and spitting with rain. Tomorrow gales are forecast. I just hope the dish stays on the pole! I shall have to lash it down before going in search of more white, plastic clips.

Click on any image for an enlargement.

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