[Elecraft] Planning the next filters

[donovanf at starpower.net]

Hi Chuck, 


The purpose of roofing filters in the K3 is commonly misunderstood, 
they're primary function is to protect the receiver from overload from 
an extremely strong interfering signal within the passband occupied 
by the signal of interest. There's an excellent paper on this topic on 
the Elecraft web site: 



http://www.elecraft.com/K3/Roofing_Filters.htm 


You can find the plots for many of the Elecraft filters here 
(caution: many of the plots use different frequency spans): 


http://www.elecraft.com/K3/K3_filter_plots.htm 


There's very little difference in the performance of the Elecraft 
400 Hz filters vs. their narrower bandwidth filters. The 400 Hz 
filter you already have is all you will ever need in all but the most 
extreme (and rare) interference situations. 


T he 1 kHz filter is a useful addition to your receiver i f you like 
broader bandwidth for casual CW operation, although the 2.1 kHz 
filter works nearly as well if you narrow the DSP bandwidth. 


There's very little difference between the 2.7 kHz stock filter and the 
2.8 kHz 8 pole optional filter except in the most extreme interference 
situations such SSB DX contests where its tighter skirts of the 
2.8 kHz are sometimes be helpful but the difference is small. 


I prefer the 2.1 kHz filter to the 1.8 kHz filter. I have both filters 
in my K3 but rarely use the 1.8 kHz filter and only under the most 
extreme inteference situations in a SSB DX contest. 


73 
Frank 
W3LPL 



On Thu, Mar 8, 2018 at 11:24 AM Chuck Chandler <chandlerusm at gmail.com> 
wrote: 

> Right now I have the stock SSB and a 400 Hz filter in both main and sub 
> rcvrs. I would like to add some a few at a time. My first priority is to 
> add a couple to the main receiver, since it is the biggest chore to get 
> to. 
> 
> I plan on a 250 Hz CW filter, but am going back and forth between the 2.1 
> and 1.8 kHz filters. I know that narrowing the DSP to 1.8 gives a really 
> difficult to understand voice signal, while the 2.1 allows in more adjacent 
> signals. However, the roofing filters may not behave in the same manner. 
> For example, the 1.8 could be set to turn on at 2.1 to take advantage of 
> skirt shape. 
> 
> I primarily DX, and operate in some contests as well. I know SSB contests 
> really need a narrow SSB filter. 
> 
> Any suggestions on the matter from those who have gone this route before? 
> 
> 73 de Chuck, WS1L 
> 
> -- 
> 
> 
> =================== 
> Chuck Chandler 
> chandlerusm at gmail.com 
> =================== 
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