903-MHz cavity filter tune-up

For reasons that will become clear in a future post or series of posts, we’ve been busy lately—don’t worry, it’s a good thing.  I did manage to sneak away from my regular (usually desk-bound analysis) work into the lab and tune-up an eBay-special cavity filter for 903 MHz with our new network analyzer.  It’s really amazing how you can dial these things in if you have the right tools.  This one is a 3-cavity filter about 10x8x3 cm.

Passband insertion loss is about 1.2 dB.  Harmonic rejection at 1.8 GHz is 70 dB down.  I’ll take it.

I also have some eBay-special helical filters that were advertised to be for 432 MHz.  So, I need to cobble up some carrier boards to try them out.  Another day, another project.

Ethan Miller, K8GU, is a regular contributor to AmateurRadio.com and writes from Maryland, USA. Contact him at [email protected].

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