[Elecraft] K3 filters

[Geoffrey Mackenzie-Kennedy]

Benny,

Group Delay is I agree a very important consideration, but I would suggest 
that another very important factor which determines how well a receiver will 
perform when the DSP is used as the main 'selectivity block', is the odd 
order dynamic range of the first IF filter and *everything* else which 
follows it, which includes the DSP. If you widen up the first IF filter or 
its skirts and do NOT have a 'strong' system, in a strong or busy signal 
environment there is a real possibility that some of the IMD products 
generated within the IF filter and / or following stages will appear within 
the DSP's passband. An AGC loop after the filter can help if its component 
parts or action do not worsen IMD, but if activated will cause weak signals 
just above the noise floor to become 'weaker', or even disappear - i.e. the 
DX you are chasing.

These comments are not only about the K3 but receivers in general.

I suppose that another problem is the cost of a 'strong' system, which 
includes that of high performance Crystal filters.

73,
Geoff
GM4ESD



Benny Aumala <benny.aumala at pp.inet.fi> wrote on
Saturday, December 01, 2007 9:31 AM



> Nobody seems to talk about Group Delay Time.

 <snip>

> I would rather use 5 xtal roofing and all bandpass DSP.