The recent discussion regarding the suitability of pass cavities as harmonic filters made me curious as to if the odd wavelength resonances really do fall well away of the base 1/4 wave resonance (IOW would a 1/4 wave cavity tuned to 150 MHz pass the 3rd harmonic at 450 MHz).
I swept a Motorola TU255 400-470 MHz cavity with 2 dB loops from 25 MHz to 3 GHz & have attached a plot of the results. The figures above each peak indicate the true minimum loss obtained via additional narrowband sweeps, since the resonances were too sharp to be accurately measured over such a large span with only 801 measurement points available. In summary, here are the insertion losses in dB at each harmonic of 450 MHz: x1: 1.9 x2: 87 x3: 50 x4: 73 x5: 78 x6: 61 Of course this is only 1 cavity, & it is the type where the loops are on opposite sides of the cavity (as opposed to the "square" Motorola UHF cavities), which may reduce spurious responses. But at least it's nice to know that this particular model does make a good harmonic filter. Bob NO6B Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
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