Very? interesting postings.? But are we using a cannon to kill a fly?? These filters are all good and do the job I am sure.? But they are expensive,? and handle hundreds of? Watts.

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Joy runs qrp. A KX2 I believe,? and she is running? 10 W at the most.? I don't think I have ever seen anyone out at Baylands who wasn't running qrp. Correct me if I? am wrong.? So we have one qrp station on 20 meters who wants to avoid interference from? other stations on other bands who are also running qrp.? Why does she need a filter that will hand hundreds of Watts and is very expensive?

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One of the things that attracted me to qrp was that you don't need a lot of money for equipment? ((at least you didn't? before Elecraft came on the scene) and I love and have their gear).

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It's easy to build a band pass filter in an altoids tin.? Hiroki how about you and I build one and see how it works.? ?Build it and test it empirically.? ?Is the challenge accepted?? The rest of you are welcome to try too.

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I love this group because they actually do ham radio.

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Doug

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Doug, yes the most I run is 10 W and usually less. I hear interference, mostly from CW stations. I'm not sure if they are on the same band that I am on or not. It seems to me it bleeds to some of the other bands. I thought a band pass filter may solve the problem. I have never used one before, but this is how I think they work. If they are on 20 and I am on 10, ?I could have a band pass filter for 10 and that would stop the interference from 20? Is this correct? The band pass filter I was talking about isn't really expensive. I think it was in the $60 range.?

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If you look at the tiny low pass filters (toroids plus capacitors) on the circuit board of your uSDX or QDX, that's the size of filtering you need for QRP bandpass filters for 10M or bandstop filters for 20M. ?Both should easily fit in a mint tin. ?Bigger filters are for power handling of RF from QRO transmitters and amps, in use or being used nearby. ?73, Ron, N6YWU

Here is my first attempt at building a bandpass filter for 20 meters.? How does it look.

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This shows marker at 14.650.? Cliff, how does it look?

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I will bring it to Pacificon and give it to her to try.? I think it will help.? I listened today.? ?Tuned to 40 meter Ft8 frequency,? loud stations.? Inserted filter, nothing heard.? Took it out, found a loud? ssb signal, Inserted filter.? Signal gone, nothing.? ?Same result on 30 and 17 meters.? Then, with the filter in, tuned 20 meter band.? Lots of signals.? I? think my tests are valid, and verify that the filter works.? The true test will been when Joy tries it at Baylands.?

Schematic of 20 meter bandpass filter.?

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What are the values for the coils? Are you using toroids or air wound coils? I want to replicate your filter.

Toroids.? 31 turns, T50-6.? 3.8uH.? I would like to see what you get.

Can you resend this file again!

Doug, I will be at Pacificon and will find you. I would love to give it a try.?

Joy

N6GO