[Elecraft] Let's Try This Again -- was "[K3] ... A 750 Hz, 8-Pole ... Filter?"

[Wayne Burdick]

It *is* difficult to build very narrow 8-pole filters with low loss.  
That's one reason Elecraft offers a 5-pole, 200-Hz unit.

5 poles is entirely adequate at these narrow widths. Our 2-kHz IMD  
dynamic range using the 200-Hz filter is outstanding.

We've had some requests to offer a 270 or 300-Hz 5-pole filter, which  
would be better optimized for narrow-shift RTTY than the 200-Hz  
filter. We're also considering a dual-passband filter (500/270 or  
500/300) that would fit in one slot.

73,
Wayne
N6KR


On Jul 15, 2010, at 10:18 AM, Jim Brown wrote:

> On Thu, 15 Jul 2010 14:53:10 +0100, Ian White GM3SEK wrote:
>
>> Agreed. 250-270Hz would be the "sweet spot" for an 8-pole filter, to
>> guarantee good sales for the manufacturer *and* good performance  
>> for a
>> range of users in heavy QRM.
>
>> Now let's see if Inrad or Elecraft take the bait :-)
>
> Hang on a minute, guys. Inrad builds a nominal 250 Hz filter, Elecraft
> tests and re-sells it, and we buy it, because we've agreed that it's a
> sweet spot operationally.
>
> The issue is that it's wider than than at the -3dB points. So the
> problem appears to be that it's pretty difficult to build an 8-pole  
> 250
> Hz filter at 8.8 MHz, and that Inrad has given up on doing better.
>
> 73, Jim K9YC
>
>
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