Of course, if we didn't want to be able to copy with equal clarity over a > 100 dB input signal range, we could dispense with a lot of this. AND do that with signals of the extremes separated by a mere 250 Hz. We are so picky. Why does anyone put up with us :>)
You selling that T-shirt in bulk? 73, Guy. On Fri, Apr 15, 2011 at 1:11 PM, Jack Smith <jack.sm...@cliftonlaboratories.com> wrote: > Only to a first approximation are filters linear. > > Usually the major source of non-linearity is in the inductors. Even > powdered iron is non-linear to some degree. Ferrite is worse, of course. > Air is pretty close to perfect. > > Capacitors are also non-linear at some level, as C is not constant with > applied voltage. NP0/C0G caps are very good, but again not perfect. > > Filter generated intermodulation problems are real and measurable. Been > there and done that and have the Tee-shirt. > > Jack K8ZOA > > > On 4/15/2011 1:01 PM, Alan Bloom wrote: >> Hi Geoff, >> >> I guess I don't understand. Filters are linear devices. How can they >> cause IMD? If the signal generator's harmonics are removed by the >> receiver filters then it is the same as if the sig gen were "clean", no? >> >> 73, >> >> Alan N1AL >> >> >> On Fri, 2011-04-15 at 11:54 +0100, Geoffrey Mackenzie-Kennedy wrote: >>> Hi Alan, >>> >>> Indeed, most receivers do have some form of filter "up front" in the front >>> end, and therein lies one source of IMD measurement error if harmonics are >>> present in the applied test signals. >>> >>> While the MiniCircuits application note AN-00-008 which Jack mentioned >>> points out that harmonics present in the applied test signals are a >>> potential source of error when measuring the IMD performance of a device >>> such as a mixer, for the same reasons error can be introduced by a >>> receiver's input filter(s). So it is essential that "clean" sources are used >>> when testing a receiver. >>> >>> 73, >>> Geoff >>> GM4ESD >>> >>> >>> On April 15, 2011 at 04:26 +0100, Alan Bloom wrote: >>> >>>> Hi Geoff, >>>> >>>> Most receivers have bandpass and/or low-pass filters in the front end >>>> that would filter out the harmonics of a square-wave test signal. I >>>> could dream up some unusual situations where the harmonics could cause a >>>> problem, but normally it would not be an issue. >>>> >>>> Alan N1AL >>>> >>>> >>>> On Fri, 2011-04-15 at 00:37 +0100, Geoffrey Mackenzie-Kennedy wrote: >>>>> Hi Al, >>>>> >>>>> You did say "normally not an issue", but when making even or odd order >>>>> intermodulation measurements on a receiver the use of RF sources whose >>>>> harmonic content is significant can and usually will lead to invalid >>>>> results. >>>>> >>>>> 73, >>>>> Geoff >>>>> GM4ESD >>>>> >>>>> >>>>> On April 14, 2011 at 22:58 +0100, Alan Bloom wrote: >>>>> >>>>>> Hi Jack, >>>>>> >>>>>> You're right that when testing a wide-band device like an amplifier you >>>>>> have to filter out the generator harmonics in order to get a valid >>>>>> third-order IMD test. But when testing a narrow-band device like a >>>>>> receiver the harmonics are normally not an issue. >>>>>> >>>>>> Those Coilcraft low-pass filters look very nice, especially for he >>>>>> price. Where can you buy them? >>>>>> >>>>>> Alan N1AL >>> >>> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:Elecraft@mailman.qth.net >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
