[Elecraft] Yet another filter question

[Joe Subich, W4TV]

The 5 pole filters all have a slight frequency offset which varies
from filter to filter.   *When used for diversity* the filter offsets
need to be matched (within 10 Hz) so a single synthesizer can drive
both receivers to maintain phase lock.

The issue is not critical with the 2.7 KHz filter as modest offsets
can be accommodated by setting both for the average.  However with
the narrow filters a 50 Hz difference in the filter center frequencies
can represent a substantial percentage of the filter passband <G>.

Fortunately, the issue can be addressed by purchasing both filters at
the same time and specifying "frequency matching."

73,

    ... Joe, W4TV


On 2015-05-17 11:21 AM, Kjeld Holm wrote:
> Dear Morgan,
> I remember something about 5 pole filters have to be paired (or what the
> exact word was) whereas 8 pole filters can be mixed without any further
> considerations.
> 73, Kjeld, OZ1CCM
>
>
> -----Original Message-----
> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Morgan
> Bailey, II
> Sent: 15. maj 2015 18:33
> To: Elecraft Reflector
> Subject: [Elecraft] Yet another filter question
>
> Hi all
>
> I apologize if this topic has been covered here before.
>
> I've had my K3 for about a year now, and I'm considering adding another
> roofing filter.  I currently have the 400 hz 8 pole filter and it has served
> me very well, but there were several instances during the 2014 WPX cw
> contest as well as 2014 SS where I needed something tighter.  I've seen the
> filter plots for the 5 pole and 8 pole filters, and while my initial gut
> feeling was to go with the 8 pole 250 hz filter, I'm now questioning whether
> or not that would be wise.  According to the plots, there isn't much
> difference between the two filters, and based on this data alone it would
> seem that the better choice would be to go with the 200hz 5-pole.
>
> I'm sure I'm missing something here.
>
> Thoughts?
>
> Thanks
>
> 73, Morgan, NS0R.
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