Re: G3WDG Boards

Chris Bartram G4DGU

Hello Andy

What we as a 10GHz community could do with, is an off the shelf, or easy to build, 10GHz bandpass filter suitable for image rejection at 144 IF.

The problem trying to use a 144MHz IF at 10GHz is akin to trying to use top band as an IF for 2m! It is very difficult indeed to design a simple, low-cost filter to reject the image adequately. That is particularly true if you wish to make it free from adjustments. I have been there!

My solution, which was available off the shelf, was a simple two-pole filter using orthogonally polarised circular WG resonators sharing the same length of guide. The design produces 50dB+ rejection at 10008MHz with between 1 and 2dB loss at 10368MHz.  I came up with that I when I designed my transverter. The design did go through a number of iterations in which I tried to eliminate adjustments. I almost got there, but the very accurate machining which was required put the costs of manufacture through the roof. The final version, while extremely reproducible, did need to see my VNA for set-up.

I have looked at other solutions using eg. resonators realised in some forms of substrate integrated waveguide. Some look promising, but other activities have interfered, and I'd like to get back on the air before I decide to do any more work on the project!


Chris G4DGU

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