Re: XG3 device...
Posted by
n7ws on
Apr 16, 2011; 1:56am
URL: http://elecraft.85.s1.nabble.com/XG3-device-tp6271930p6278143.html
Getting a little far afield here and maybe a little pedantic (can you be just a little pedantic?) mixer technology has progressed to the point that the mixer no longer has to be the limiting factor.
Input filters and post mixer crystal filters are now the focus.
"After having concentrated on the H-Mode mixer circuit for quite some time and looking at the results obtained with the combination of FSA3157 switches and T1-6T transformers, it was clear that at this point the mixer was not the weakest chain in the receiver's frontend anymore." from:
http://www.xs4all.nl/~martein/pa3ake/hmode/frontend_intro.html--- On Fri, 4/15/11, Alan Bloom <
[hidden email]> wrote:
> From: Alan Bloom <
[hidden email]>
> Hi Geoff,
>
> The case we're considering is where the test signal(s) are
> near the
> receiver tuned frequency so they are well within the
> passband of the
> input filters.
>
> If the receiver's in-band dynamic range is significantly
> affected by
> non-linear filters in the front end, then that is a serious
> design
> error. The distortion should be dominated by the
> mixer, not the filter.
> If the filter is distorting then it doesn't matter if the
> generator has
> harmonics - you're hosed anyway.
>
> For in-band receiver testing, generator harmonics should
> not matter.
> The only exceptions would be for receivers that do not have
> filters
> protecting the front end or perhaps the exceedingly rare
> case where a
> generator harmonic happens to fall on a receiver image or
> spur frequency
> (easily fixed by changing the test frequency
> slightly). But in almost
> all cases the harmonics should not matter.
>
> Alan N1AL
>
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