[Elecraft] start without ANY extra roofing filters....

[Geoffrey Mackenzie-Kennedy]

The IMD contributed by inductor cores used in the front-end selective 
circuits is often not taken into account either, or for that matter any core 
within the signal path. They can bite.

73,
Geoff
GM4ESD


Larry Phipps wrote:

> This is a subject which seems to be gaining in importance as receiver 
> designs surrounding the xtal filter seem to be improving to the point 
> where the filters are becoming the limiting factor in IMD performance.
>
> 73,
> Larry N8LP


>> 1.  Narrower is not always better (Ten-Tec experience)
>> 2.  8-poles is not always better than 5-poles (per Inrad)
>> 3.  Let IMD and BDR measurements be your guide
>>
>>         More evidence below to support waiting for IMD/BDR measurements 
>> before ordering any roofing filters.
>>
>>                                 73,  Bill  W4ZV
>>
>> http://mailman.qth.net/pipermail/1000mp/2007-April/020755.html
>>
>> There is a fascinating article describing IMD tests on the IC-7800 by 
>> DC4KU
>> in CQ-DL, August 2005 (in German). In these tests, IP3 at 2 kHz offset
>> degrades by an astounding 16 dB when switching from the 15 kHz to the 6 
>> kHz
>> roofing filter. This degradation is due to passive IMD in the filter, and
>> possibly also to IMD in the filter driver amplifiers caused by mismatch 
>> when
>> the filter is excited outside its passband. I can send you an
>> English-language summary of the relevant part privately, if you wish.

<snip>