Hi Jeff, > "Jeff DePolo WN3A" <[EMAIL PROTECTED]> wrote: > Even pass cavities don't necessarily attenuate harmonics > produced by a circulator sufficiently.
This is true, it's all a game of numbers and good test equipment. > A 1/4 wave cavity will have a very good pass response at 3/4 > wave (3rd harmonic). Even at other harmonics, or between > harmonics, a bandpass cavity isn't necessarily going to give you > adequate attenuation of the harmonics. The large fly in the soup is the 2nd Harmonic. People should also be aware of UHF Cavities which are 3/4 wave, much betta' For single unit operation, one of the better layouts is the circulator followed by at least a 5 pole low pass filter, the output sent to a band pass, band reject duplexer. > A pass can is always good practice on any transmitter, but a > one-stop-shopping cure for isolator harmonics it is not. There is no cure, only practical harmonic reduction techniques. > And be careful of the varieties of "harmonic filters" out there. > Some of the cheaper ones are just 2nd harmonic traps. They'll > knock down the 2nd harmonic by 40 dB or so, but do nothing for the > 3rd and higher harmonics, which can really be a problem on highband > (3rd harmonic ends up on UHF). A real low-pass filter is what > you should use. > Jeff Low pass filters are most often supplied/recomended with circulators. They are actually simple to make, most often commercially priced +13dB or higher than the actual parts used to make them. The real story is told with good test equipment. cheers Skipp skipp025 @yahoo.com Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
