[Elecraft] K3 - Is 2.7k filter required in KRX3?

[Joe Planisky]

I recently installed a KRX3 in my K3.  I currently only have the 13kHZ  
and 400Hz filters installed in it.  (This is a temporary situation as  
I'm waiting for a matched 2.7kHz filter from Elecraft.)  The filters  
are configured correctly according to both the CONFIG menu and the K3  
Utility.

The problem is I get no output from the sub RX when the bandwidth is  
450Hz or 500Hz in CW and DATA modes.

I get continuous output as expected at all bandwidths in SSB mode.

If I configure the 400Hz filter as a 500Hz filter, I get continuous  
output in all modes.

In all cases, I see the FL1 and FL5 icons on the LCD change at the  
appropriate BW settings.

I'm wondering if perhaps the 2.7kHz (or 2.8kHz) filter is required for  
proper operation of the KRX3.  Admittedly this is an unusual  
configuration, and assuming the problem goes away when I plug in the  
2.7k filter, it's no big deal.

I'm running FW 3.27 / DSP 2.25.

73
--
Joe KB8AP