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one final filter: wavetrap for one BB frequency
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I have one final filter I'd like to construct in the next day or so, a frequency notch for one broadcast band station.? This would be used during times when I'd want to listen to the BB, but not be overwhelmed by the station close to me.? I've looked at Elsie and the RF Tools website I used to help with the prior filter, but, unless I'm missing something, they don't cover this type of filter.
Your thoughts would be welcome. Thanks, Jon |
a frequency notch for one broadcast band station.? This would be used during times when I'd want to listen to the BB, but not be overwhelmed by the station close to me.Jon Be aware that moving the LO frequency will move these "harmonic" responses away from a wanted frequency. A response 3 times the wanted frequency moves 3 times as fast as the wanted signal. Any signals still getting through your filter may be shifted away. Top marks for perseverance! A simple series adjustable resonance inductance/capacitance is often used as a notch. 73 Alan G4ZFQ |
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That would be my recommendation. For a single frequency, a simple series LC
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circuit is easy to build and tune. 73, Zack W9SZ On Tue, Jul 6, 2021 at 12:19 AM Alan G4ZFQ <alan4alan@...> wrote:
aJon |
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My first one seems to be doing the job.? I took one of the spare T50-7 toroids from the band stop filter project and placed it in series with a couple of the spare poly caps.? Used TinySA for close alignment, then finished up with signal generator and frequency counter.? About 30-35 dB reduction.? This may be enough, will just have to listen and see over the next few days.
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I'm not sure I shouldn't include a 500 pF mica compression trimmer for future adjustment, but if the toroid and poly will maintain their stability, I may not need it. Jon On 7/6/21 8:39 AM, Zack Widup wrote:
That would be my recommendation. For a single frequency, a simple series LC |
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