[Elecraft] K3 Filter Configurations and Explanations

[Bill W4ZV]

Dick Dievendorff wrote:
> 
> 
> If you're interested in CW or "data" modes (RTTY, PSK, etc), then you'll
> perhaps want to invest in one or more narrower filters, perhaps one or two
> of 200, 250, 400, 500 Hz.  If it's only one narrower filter, I'd suggest
> either the 400 or 500 Hz filter. I think of the 200 and 250 as
> alternatives
> and 400 and 500 as alternatives.  I wouldn't think you'd want both 200 and
> 250 nor would you probably want both 400 and 500.
> 

The 400 and 250 are actually very close in bandwidth.  According to
Elecraft's own measurements below, the 400 actually has 435 Hz BW and the
250 is actually 370 Hz, both with the same shape factor.  You definitely
don't need to spend $250 total for two filters that only differ in BW by
about 15%.  Also note that the 2.7k actually has slightly wider BW than the
2.8k. 

Filter  BW(-6dB)     Shape Factor
 200     224             4.0
 250     370             2.1
 400     435             2.1
 500     565             3.1
1000    1063             1.6
1800    1913             1.5
2700    2910             2.9
2800    2888             1.6
6000    6125             1.5 

http://www.zerobeat.net/mediawiki/index.php/K3_Roofing_Filters

FYI my 2.7k/1.0k/500 are in close agreement with the above measurements but
my 200 is slightly less than 210 Hz.

73,  Bill  W4ZV
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