[Elecraft] Rethinking filters

[Joe Subich, W4TV]

> In his annual Dayton talk yesterday, Rob Sherwood said that he had
> seen some serious IM issues with some Elecraft roofing filters.

I've been e-mailing with Rob - some of my spare filters have been among
his test subjects.  The issue is passive IMD in the filter itself ...
in essence when the interfering signal levels get high enough, the
filters start to behave as non-linear devices and seem to develop a
short term "memory."   This applies to both the 5 pole and 8 pole
filters.

Of note is that the signal levels necessary to generate this passive
IMD is nearly 10dB higher than the former reciprocal mixing (phase
noise) limited dynamic range values with the "old" synthesizer.  It is
much like pealing an onion ... once one limitation is removed another
item in the signal chain becomes the weak link.

It may be necessary to test filters to a higher standard.  I understand
some test systems are already under development.

73,

   ... Joe, W4TV


On 2015-05-15 8:02 PM, Jim Brown wrote:
> On Fri,5/15/2015 3:39 PM, Jim Miller wrote:
>> I've got my K3S on order and was planning to transfer some of my filters
>> from my K3 before selling it but after reviewing the filter specs along
>> with my past experience I'm rethinking the narrow end.
>
> In his annual Dayton talk yesterday, Rob Sherwood said that he had seen
> some serious IM issues with some Elecraft roofing filters. I would hold
> off on buying any new filters for a while until I knew a lot more about
> that issue.
>
> 73, Jim K9YC
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