[Elecraft] What CW Filters do others have

[Ron D'Eau Claire]

Remember that your K3 already has a variable bandwidth DSP filter that will
take you all the way down to 50 Hz! 

In asking about a "CW filter" I'm assuming you are considering what
additional crystal filter you might want. 

A narrower bandwidth crystal filter does one thing for receiving narrow
signals like CW; it helps avoid overload from extremely strong signals near
the one you're copying. With a wide dynamic range receiver like the K3, that
means the strong signal must be very, very strong to cause trouble. Usually
the first sign of trouble from a very strong signal inside the bandpass of
your crystal filter is that the K3's hardware AGC will sensee it and the
gain level will begin to "pump" with the keying even though you cannot hear
the signal because it is stripped out by the DSP filter.

The quick response to stop that is to reduce the RF gain control.  

Having a narrow(er) crystal filter will reduce the possibility of that
happening. With a 2.7 kHz SSB filter, all the huge signal need be is
somewhere inside that 2.7 kHz bandpass. Of course that can and will happen
with narrower filters too. It's just that the likelihood of it happening is
reduced with narrower filters. 

Having an 8 pole instead of 5 pole filter offers a very slight extra
advantage in the event you are trying to work a weak signal right up against
a very, very, strong signal since the skirts on the 8-pole filter are
steeper, providing more signal rejection for signals near the edge of the
passband. 

You are probably aware that the crystal filters are selected automatically
as you change the DSP filter bandwidth with the WIDTH knob so, normally, you
are completely unaware of the actual crystal filter in use unless you check
the display.    

As a CW operator I have a 400 Hz filter. But, not being a contester or DX-er
who dives into high-powered pileups or living in very close proximity to
another Ham, I've probably never needed it. Indeed, 90% of my operating is
with the bandwidth out around 1 kHz so I can keep track of what is happening
around the frequency of my QSO, so my 2.7 kHz crystal filter is in use. I
can't recall ever having another signal strong enough to upset the K3 or
pump the AGC within the passband, although I have often enough cranked down
the DSP filter to narrow bandwidths to copy weak(er) signals which, if I
crank the WIDTH down to 400 Hz or less, automatically switches in the 400 Hz
crystal filter. 

73, Ron AC7AC 


-----Original Message-----

I am ready to pull the trigger on a CW filter for my K3.  I am curious to
hear opinions of others who have used the 8 pole 400hz filter and the 5 pole
500hz filter.  I am not a contester by any means so this is for casual CW
operating.

All thoughts and opinions are welcome!

Thanks!
AC8JD



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