[Elecraft] adding 250Hz filer, any improvement?

[Bill W4ZV]

wayne burdick wrote:
> 
> On the other end of the spectrum: If the going is really tough, you  
> might consider our 200 Hz, 5-pole filter. It's a favorite of CW and  
> data-mode operators who routinely have to dig for weak ones between  
> monster signals in CW and data modes.
> 

I operated most of the CQ 160 (a very crowded contest with a mixture of big
NA signals and weak DX signals) using a 200 Hz set to activate at WIDTH 350. 
This makes the XFIL/DSP cascaded curve closer to that of the 200 only.  Joe
W4TV provided the following a few years ago:

                 200      250     400      500
   -------------------------------------------------
    - 6dB      224      370     435      565  Hz
    -60dB      896     777     913     1751  Hz
     slope     6.22     3.77    4.43    10.98 Hz/dB  

    -10dB      274      400     470      653  Hz
    -20dB      398      475     559      873  Hz
    -30dB      522      550     647     1092  Hz
    -40dB      647      626     736     1312  Hz
    -50dB      771      702     825     1531  Hz

http://elecraft.365791.n2.nabble.com/FILTER-SETTINGS-td456756.html#a456757

With the XFIL = 200 and DSP = 350,  the resulting filter is probably -15 dB
at ~300 Hz, which still allows you to still hear what's going on around you. 
Most EU stations would call zero beat since they are accustomed to extremely
tight spacings but many NA stations were off frequency.  Sandwiched between
two EU stations about 250 Hz on either side, a major problem was when NA
stations called them on my run frequency!

I use a waterfall when doing S&P so it was very easy to jump to stations
using the 200 Hz filter.  I believe as more guys begin using waterfalls they
will do a better job of zero beating stations running.  One problem I ran
into was my KRX3 only had an Inrad 500 Hz 8-pole which was definitely too
wide with many strong stations were nearby.  I had to turn diversity off
several few times when the KRX3 was allowing too much QRM.  I fixed that
last week by adding another 200 Hz to the KRX3!

73,  Bill

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