http://elecraft.85.s1.nabble.com/Fwd-New-Sherwood-report-tp5793377p5806127.html
tones above vs. below the filter passband.
... Joe, W4TV
> I haven't (yet) seen Rob's comments, cited by Paul. The designers across the pond are well-aware of the IMD effects in crystal filters, for example here:
>
>
http://www.xs4all.nl/~martein/pa3ake/hmode/roofer_intro.html>
> I have searched for, but have not found, remarks that I recall being made by Wayne that said that Elecraft screens its filters for IMD.
>
> (I wish they also screened for bandpass symmetry, my 2.8 KHz is very disappointing in that regard)
>
> So considering the potential effects of asymmetry in the build of the filter(s) it doesn't surprise that reversing the filter might make a difference, *if* filter IMD is the dominate factor.
>
> --- On Thu, 12/2/10, Paul Christensen<
[hidden email]> wrote:
>
>
>
> On the Ten Tec Eagle list, Rob Sherwood just posted a very interesting
> response to the 2 kHz DR rankings being discussed here. Apparently, there's
> a measurable amount of IMD difference not only between roofing filter
> production samples, but the manner in which they're inserted. For example,
> on the Orion II, he gets variations of several dB on close-spaced DR just by
> unplugging a filter and reversing it -- something not possible with the K3
> since the pin-out isn't symmetrical. He goes on to discuss why.
>
> Sounds like we could probably take handful of INRAD filters and choose the
> best ones that may likely be equal to the FTdx-5K under most, if not all
> narrow filter positions in the K3.
>
> On multiple occasions, Rob has stated that once you get up anywhere near
> these numbers, a prospective purchaser should be looking at other
> performance factors and features. Probably if you're within the top ten or
> so on his list, you would be pretty hard-pressed to notice any differences
> when other factors (e.g., the other guy's bandwidth) will mask incremental
> improvements to close-spaced DR.
>
> For me, those "other factors" that Rob discusses include low distortion, low
> noise AF sections, low TX IMD, and super fast, click-free T/R times. Right
> now, those are the most important factors to me now that basic receiver
> performance has advanced so much in the past decade.
>
> Paul, W9AC
>
>
>
>
>
>
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