Re: Winding toroids

Curt M.
 

I wanted to build a set of the basic band pass filters for field day ops and didn't have a network analyzer.  I used the K4VX article from 1988 which calls for the grid dip meter.

https://www.arrl.org/files/file/Technology/tis/info/pdf/8809017.pdf 

I bought a used but in excellent condition Millen 90651 GDO off of eBay.  I REALLY enjoyed using it for that project.  Using the GDO and then verifying the he resonate frequency with a loop of wire to my frequency counter, It got me so close when tuning the LC pairs.  With only a slight adjustment of the windings once everything was in place and connected through my RigExpert antenna analyzer and to a dummy load, I now have 4 of the 5 filters that I built and working perfectly.  I verified them once tuned on a friend's network analyzer with tracking generator and they passed with flying colors.

The 40, 20, 15 and 10m filter work great.  I didn't need the 160m filter so I didn't build that one.  The design based on the article for the 80 meter filter does work but it's such a narrow band pass that you'd probably have to build 3 different filters and tune them each to 1/3 of the band with a little overlap to cover the 80m band.

In that application the GDO allows you to see just how alive an LC pair is with respect to the number of windings and their spacing.   That technology still stands the test of time in today's modern day.

Curt M.

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