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Author Topic: DGPS Bandpass Filter Construction Project  (Read 2080 times)

Offline ChrisSmolinski

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DGPS Bandpass Filter Construction Project
« on: July 04, 2017, 2021 UTC »
In my never ending quest for more and better DGPS logs, I built a bandpass filter.  I used an online design tool, and came up with the following schematic:

I used the Butterworth filter values, although due to the difficulty in getting exact component values, the actual filter probably behaves slightly (or maybe not so slightly) different from the design. I put components I had in the parts bins in parallel and series as best as I could, to get close to the specified values. For example, the 3.17 uH inductors are actually three 10 uH inductors in parallel, so that's closer to 3.33 uH. Except they probably aren't really 10 uH.

I like to use one pint paint cans for building RF projects like this, as I have a box of them, the geiger tubes I buy for the radiation detectors I sell come in them. Hey, want to by a geiger counter?? Check out this link: http://www.blackcatsystems.com/GM/

The following screenshots from SdrDx show how the actual passband. It does a pretty good job of covering the DGPS band, with a little bit of a safety factor on each side.  And does a great job of blocking the MW band. The horizontal lines you see are lightning discharges from some storms tens of miles away at the time the screenshots were taken. The DGPS band runs from 285-325 kHz.

Next step is to see how it performs overnight. The real test will be once we leave summer and enter Autumn and Winter.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 900 ft Horz skyloop / 500 ft NE beverage / 250 ft V Beam / 58 ft T2FD / 120 ft T2FD / 400 ft south beverage / 43m, 20m, 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline skeezix

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Re: DGPS Bandpass Filter Construction Project
« Reply #1 on: July 05, 2017, 2245 UTC »
Very nice.

But, will it actually help with decodes?
Minneapolis, MN


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