Re: Dish feed


Hi Jim,

Thanks. It looks like that would work. The tubing is not expensive, so I don't have a lot to lose in getting some of it and experimenting.

73, Zack W9SZ

On Thu, Aug 20, 2020 at 1:32 PM Jim Moss <n9jim@...> wrote:
I used 0.45 wall 4/2mm and also 4/3.1 and 3/2.1 mm K&S tubing from McMaster-Carr.  Worked great for connecting out of the coupler into my application antenna.  Also found that standard 0.5 wall 4/3mm and 3/2mm would telescope fine. Just be careful in cutting.

On Aug 20, 2020, at 9:49 AM, Zack Widup <w9sz.zack@...> wrote:

I've been thinking of using a 1 foot diameter prime focus dish with the transverter. The Chaparral-type feed has two parts - the one that attaches to the board and the Chaparral feed itself. I was thinking that it might be possible to use a piece of brass tubing with an outside diameter of 5/32 inches (0.156 inches, ~ 4 mm) with an inside diameter of 5/64 inches (0.078 inches - ~2 mm). Brian WA1ZMS told me that the SHF Micro 1 foot diameter dish performs acceptably at 122 GHz. He has even used one at higher frequencies. I am currently using this dish with a piece of brass tubing (circular waveguide) and a reflecting plate on 76 GHz.

The f/D ratio for this dish is 0.6. That gives a focal length of 7.2 inches. I can machine a short section of 5/32 inch diameter brass rod with a center hole 5/64 inches in diameter, but I can only machine a couple inches. I could possibly use another piece of brass tubing with an ID of 5/32 inches to connect to this that would be long enough to use as the feed. I inquired of K & S Metals about the cost of a brass tubing that has an OD of 5/32 inch and 0.04 inch thick walls. This would give an ID of 0.076 inches, which would be acceptable. They told me there is a minimum order for 12-inch sections of this tubing of 24 at $4.17 each. I neither need nor want to purchase 24 of them unless someone wants a group order.

Any discussions or suggestions on this?

73, Zack W9SZ


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