Re: XG3 device...
Posted by
Alan Bloom on
Apr 15, 2011; 5:01pm
URL: http://elecraft.85.s1.nabble.com/XG3-device-tp6271930p6276998.html
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/elecraftHelp:
http://mailman.qth.net/mmfaq.htmPost: mailto:
[hidden email]
This list hosted by:
http://www.qsl.netPlease help support this email list:
http://www.qsl.net/donate.html