Just Sharing This Adapting a Prodelin Polariser.

[John]

For something to do while the cold wet weather is with us , here is a little project to modify a standard Prodelin C-band polariser with motorised polarity / skew for use on a Elite 2.2 PF antenna. It will basically be the same as the AV-Comm polariser barrel one in use now and some performance comparisons between the two can be done later.
Here's a few pics of the Prodelin & AV-Comm in use now for starters.
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[John]

As can be seen, the Prodelin polariser is a much more refined piece of engineering. This new fabrication is really only a prototype with not too much time spent on making it look too pretty & also only minimal basic tools used - The first bit of the new fabrications started at the front end of the polariser with the task of making a section of waveguide to attach the PF scalar ring to. My first waveguide is using a section of tube that is the same internal dimension of the AV-Comm barrel and a quick and cheerful mounting plate to hold the scalar ring was made out of a spare unused scalar ringscalar ring.
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[John]

.. Next thing on the to do list - - put together a square section lnb support arm bracket to replace the circular section AV-Comm polariser bracket so quickly knocked up this one shown in it's primer paint and still unfinished.

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[John]

.. Moving on to the trickier bit - producing a smooth rotating RF tight as best as can be achieved joint between the Prodelin polariser and the beautifully machined lnb flange assembly. In normal configuration the polariser had a 5mm x 2.4mm deep channel for the rubber weather seal at one end and the lnb assembly also had the same dimension channel. Luckily the polariser has the exact dimensions inside from one end to the other so it didn't matter which way around it pointed at the dish face - - this proved to be a big bonus as the two machined seal channels matched up perfectly when the polariser and lnb assembly were placed together and basically formed a nearly 5mm square channel-ideal for inserting the right amount of 5mm stainless ball bearings to form a continuous metal RF seal and also a nice smooth rotating joint. The next problem was how to find a cheap way to keep the two assemblies together. A few pics below to go with this narrative.
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[moonbase]

@John

Excellent modification, well done. Signal reports soon I hope?

 

[Channel Hopper]

That grease is going to flow well once it gets a little warmer, down into the feed and over the cap/spider trap (if you have one that is) , is it worth rethinking your strategy to use a molybdenum paste instead ?

 

[John]

@John

Excellent modification, well done. Signal reports soon I hope?

how soon i can get it transfered onto the 2.2 MB depends on the weather at the moment, we've had a couple of really wet cold days up here and it's not been very pleasant. It might not turn out very good Dave, my AV-Comm set-up works very good but the fun is in trying lol. I should have said in my previous post re: the rubber weather seals or lack of now, that i will have a close fitting rain canopy over the joint area to keep the rain out a bit.

 

[John]

That grease is going to flow well once it gets a little warmer, down into the feed and over the cap/spider trap (if you have one that is) , is it worth rethinking your strategy to use a molybdenum paste instead ?

Yes you're right in theory and i have already done that test on the joint here in the shack with very warm ambient surrounding and it didn't run. Good point though- i'll look into that suggestion further. You been in the shed rummaging yet ?.

 

[Channel Hopper]

Always rummaging, yes I have C band scalars in sight but they are not Prodelin, and modified for offset/side by side fitting.

 

[John]

Always rummaging, yes I have C band scalars in sight but they are not Prodelin, and modified for offset/side by side fitting.

.. thanks for the rummage CH, i have some chopped versions like that myself so will pass thankyou.

 

[purplemarina]

Yes your right in theory and i have already done that test on the joint here in the shack with very warm ambient surrounding and it didn't run. Good point though- i'll look into that suggestion further. You been in the shed rummaging yet ?.

high melting point grease ie wheel bearing grease may be a option. Great Mod !

 

[Channel Hopper]

Since the only material in there that will rust are the bearings , why not change them for stainless if not already ?

loose ball bearings stainless | eBay

 

[John]

Since the only material in there that will rust are the bearings , why not change them for stainless if not already ?

loose ball bearings stainless | eBay

Post 4..... > inserting the right amount of 5mm stainless ball bearings <

 

[Channel Hopper]

No grease required then, just lacquer the aluminium surfaces.

 

[John]

No grease required then, just lacquer the aluminium surfaces.[/QUOTE



Been using this on my exterior projects for waterproofing connections & surfaces to good effect

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View attachment 121367

 

[scopus]

Is it up and working yet??

 

[John]

No grease required then, just lacquer the aluminium surfaces.

Been using this on my exterior projects for waterproofing connections & surfaces to good effect

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[John]

Is it up and working yet??

Not yet -

 

[John]

... Next to do - - find a cheap and cheerful way to mate the two together.
A Lazy Susan bearing was considered as i have used them before to some success but this was not possible on this build /mod due to aperture size mis-match.
Solution was to use sealed miniature bearings that are used in model RC cars etc, knock up some simple mounting brackets, drill and tap the fixed Prodelin polariser outer rim and fix them to it. Final assembly will be sprayed with Plastic Seal and also have some sort of close fitting weather canopy fitted.
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[John]

... sunshine and showers here today but made a start on stripping out the circular shaped motorised AV-Comm polariser set-up on the 2.2 ready for the critical re-alignment of the motorised square section Prodelin polariser tomorrow weather permitting. Will be using a four string approach to aligning the feed throat to exact central feed position and for correct geometry down the boresight etc.
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