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Re: [TowerTalk] Using Stubs to Reject Harmonics

 To: lists@subich.com, "Tower and HF antenna construction topics." , "'Tower and HF antenna construction topics.'" , TexasRF@aol.com Re: [TowerTalk] Using Stubs to Reject Harmonics Jim Lux Jim Lux , "Tower and HF antenna construction topics." Tue, 2 Feb 2010 18:33:14 -0800 (GMT-08:00) mailto:towertalk@contesting.com>
 -----Original Message----- >From: "Joe Subich, W4TV" >Sent: Feb 2, 2010 4:48 PM >To: "'Tower and HF antenna construction topics.'" , >TexasRF@aol.com >Subject: Re: [TowerTalk] Using Stubs to Reject Harmonics > > >> 1/4 wavelength at the second harmonic is only 1/8 wavelength at >> the operating frequency. If you make the connection 1/4 wavelength >> away at the operating frequency, the described transformation does >> not happen at the second harmonic. > >Which is why W2VJN's stub cookbook shows some interesting behavior >with 1/8 wave connecting lines . Without getting the book off >the shelf, I believe he was using 1/8 wave between the amplifier >and first stub and 1/8 wave between first and second stubs in some >cases to optimize 2nd harmonic rejection. > >1/16 wave would be another interesting connecting length if the >4th harmonic were the bigger problem ... the combinations are >endless . > >73, > Which is why a computer to model it is nice... Or a set of decent design equations. I'll bet there's a nomogram or set of templates for a Smith Chart that does this kind of thing, at least for a fairly simple 1, 2, or 3 stub setup. It's not much different than using a multistub tuner at microwave frequencies. After you do it a few times, you get a feel for what the various stubs are doing. If you have a network analyzer, it's even more fun, because you can see the S11, S22, and S21 all at the same time. I will say, though, that for multiple stubs, doing without explicit calculation is somewhat of an art. There are people who can tune up a multi section filter quickly, and those who can't. Jim _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk
 Current Thread Re: [TowerTalk] Using Stubs to Reject Harmonics, (continued) Re: [TowerTalk] Using Stubs to Reject Harmonics, Jim Brown Re: [TowerTalk] Using Stubs to Reject Harmonics, Joe Subich, W4TV Re: [TowerTalk] Using Stubs to Reject Harmonics, Jim Hargrave Re: [TowerTalk] Using Stubs to Reject Harmonics, Gary Schafer Re: [TowerTalk] Using Stubs to Reject Harmonics, TexasRF Re: [TowerTalk] Using Stubs to Reject Harmonics, Joe Subich, W4TV Re: [TowerTalk] Using Stubs to Reject Harmonics, Paul Christensen Re: [TowerTalk] Using Stubs to Reject Harmonics, Jim Lux Re: [TowerTalk] Using Stubs to Reject Harmonics, Richard (Rick) Karlquist Re: [TowerTalk] Using Stubs to Reject Harmonics, Jim Lux <= Re: [TowerTalk] Using Stubs to Reject Harmonics, Jim Lux Re: [TowerTalk] Using Stubs to Reject Harmonics, TexasRF Re: [TowerTalk] Using Stubs to Reject Harmonics, Paul Christensen Re: [TowerTalk] Using Stubs to Reject Harmonics, Jim Brown Re: [TowerTalk] Using Stubs to Reject Harmonics, Michael Tope Re: [TowerTalk] Using Stubs to Reject Harmonics, TexasRF [TowerTalk] Coax Loss -- RG-Numbers Don't Tell us Much, Jim Brown