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
