Re: Harmonics measured by Warren. How bad?

Warren Allgyer <allgyer@...>

I set out to design a bandpass filter that could replace Filter 4 for use on 12 and 10 meters. I wanted to see if it was possible to design a simple filter that had steep enough skirts to attenuate both the harmonics and the "45 MHz - Carrier" spurs. I wanted to see how simple a filter could be and still meet this requirement.

Here is a very simple third order filter that appears to fill the bill. Shown are the original design, the actual implementation, and the measured results. It does the job (just barely, in the case of 12 meters but good enough) and is only a third order filter as opposed to the fifth order designs for the original low pass Filter 4.

I used the online 66Pacific toroid calculator which called for 5, 20, and 5 turns respectfully on T-6-25 cores. I ended up measuring and trimming these to 4,17, and 4 in the final design. Similarly, the design called for 480, 32, 480 pf for the caps..... I ended up using 440 (2 x 220), 27, 440 pf to get the profile shown in the measured spectrum. 

In the end, one filter that meets both harmonic and spur requirements at 2 watts. It can be done!




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