[Elecraft] K3 Filter selection

[Joe Subich, W4TV]

> I think you are generalising from a single sample.

No, that is INRAD's own specification and is found in the filter 
curves on both their web site and in the 8 pole curves on the 
Elecraft site.  The same was true with the Fox Tango filers before 
the filter line was acquired by W2VJN many years ago. 

All of the filers are slightly wider than "nominal" so that the 
effective bandwidth of two cascaded filters (e.g., 8 MHz and 
455 KHz) is approximately nominal.  Unfortunately, the 8 and 
9 MHz filters in particular are significantly wider than the 
notational value in the narrow values - more than necessary to 
maintain the desired bandwidth in cascade. 

73, 

   ... Joe, W4TV 
 


> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of David 
> Woolley (E.L)
> Sent: Thursday, May 29, 2008 6:04 AM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 Filter selection
> 
> 
> Bill W4ZV wrote:
> 
> > 
> > 400 and 250:  A waste of money IMHO.  Since the 400 is actually 435 
> > and the 250 is actually 370, there is only 65 Hz difference in this 
> > combination and you'll probably never notice the difference between 
> > them (370/435 = only 15% narrower).  Total cost $250.
> 
> I think you are generalising from a single sample.
> 
> It may well be the case that to  guarantee a bandwidth of at 
> least 250 
> Hz, without doing expensive select on test procedures for the 
> capacitors, one will have some samples at 370 Hz.
> 
> What you may be getting is 250Hz with a given shape factor, but 
> individual units may achieve that shape factor by going flat 
> to a higher 
> frequency and then cutting off much more sharply.
> 
> -- 
> David Woolley
> "The Elecraft list is a forum for the discussion of topics related to 
> Elecraft products and more general topics related ham radio" 
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