[Elecraft] Roofing Filter question

[Jim Brown]

On Thu, 18 Dec 2008 08:14:51 -0800, Joe Planisky wrote:

>I recently added the 400 Hz  
>filter and so far, it makes virtually no difference EXCEPT in the case  
>where there's a strong signal within +/- 1 kHz or so of the station  
>I'm trying to work.  Note that a "strong signal" might be another ham  
>station, a broadcast station, RFI, etc.

Yes. Remember that the IF in the K3 has EXTENSIVE IF filtering that 
perform the function of crystal filters in older radios. Those filters 
can be adjusted (front panel knob) to virtually any bandwidth between 50 
Hz and 6 kHz, and are the equivalent of a selectable filter bank of 20 
or more expensive filters!  The roofing filter simply sits IN FRONT OF 
these IF filters. It protects them from overload, AND provides 
additional skirt selectivity. 

The radio works fine for routine use with nothing more than the stock 
2.7 kHz roofing filter. The roofing filters simply improve performance 
under difficult conditions. I own two K3s, one with 400 Hz and 1.8 kHz 
filters, the other with only a 400 Hz filter. I operated from two QTHs 
during the SSB weekend of Sweepstakes. At one QTH I had the 1.8 kHz 
filter, at the other I did not. The 1.8 kHz filter helped, but I was 
still quite happy with the radio that didn't have the 1.8 kHz filter.  

73,

Jim K9YC