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Author Topic: Is a low pass filter necessary?  (Read 28241 times)
KC4ZGP
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Posts: 1637




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« Reply #15 on: April 18, 2017, 12:14:39 PM »


My question.

The low pass filter blocks frequencies above the cutoff. Correct.

If you block some folks from entering your house, they go back from where they came.

Do the blocked frequencies do the same? Go back from where they came...the amplifier output...high SWR?

I tried this:

no filter...Bird meter twixt the antenna and amplifier ...low SWR.

with filter...Bird meter between the filter and antenna...low SWR.

with filter...Bird meter between the amplifier and filter...high SWR.

Hmmm....

73

Kraus

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KF7CG
Member

Posts: 1192




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« Reply #16 on: April 28, 2017, 11:05:56 AM »

That is why some of the more exotic interference filters contain both high-pass and low-pass filters together. The high-pass goes to ground and the low-pass goes to the antenna if trying to remove harmonics and the like. This setup will have a more consistent SWR.

KF7CG
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