[Elecraft] K3 Filter Choices

[Don Wilhelm]

  Mark,

This question is asked over and over, and you will get answers all over 
the board.
The real answer is that a lot of your filter choices will depend on what 
kind of operating you will do and in what modes.
If you do a lot of contesting or work DX in heavy pileups where there 
are a lot of strong stations close to what you want to hear. then you 
should have only the 8 pole filters, their skirts are a little bit 
steeper - BUT - these are only roofing filters, the DSP takes care of 
most of the filtering, and does it quite well.  If you will be adding 
the KRX3, the filters must be matched for diversity reception, so the 
simple way is just to use the 2.8 kHz filters.

In fact, the DSP filtering is good enough to be used alone, it goes down 
to 50 Hz width - but the DSP can only do its job if the ADC is not being 
overdriven - the hardware AGC does protect from that, but will result in 
"pumping" of that hardware AGC if there a quite strong (S-9 +20 or more) 
nearby signals.  The K3 roofing filters will knock down the strength of 
those nearby signals to a point where the hardware AGC is not activated.

Eric Swartz has posted some information for making filter choices on the 
Elecraft website, I suggest you read that too.

Bottom line is that you will have to review the type of operating that 
you will do with the K3 and select your filters from that information.  
If your operation is rather casual, you may only need the stock 2.7 kHz 
filter.

If you want to transmit either AM or ESSB or you want wide bandwidth SWL 
reception, you will need the 6 kHz filter, and if you want to either 
transmit or receive FM, you will need the 13 kHz filter.

Another option is to wait and see - order your K3 with the stock filter 
(or perhaps the optional 2.8 8 pole filter), and operate for a while to 
determine your usual DSP-set bandwidths for each mode you use - that 
information will reveal the filters that you will derive most benefit from.

A word of caution on my above suggestion - if you will install the KRX3 
immediately, you must remove it to add more filters, and that operation 
has been referred to as a "shoehorn operation", so your choice is to 
guess at the filters needed and order them up front or delay the 
installation of the KRX3.  Without the KRX3 installed, the filters are a 
breeze to change.

73,
Don W3FPR

On 10/3/2010 7:27 PM, pastormg2 at verizon.net wrote:
> Hi Guys, in my quest to purchase a new K3 I am worndering about 8 pole filter choices.  I see that there is a 1.8 KHZ 8 pole ssb filter and a 250 HZ 8 pole cw filter that is avaiable.  If one purchases one of these filters wouldn't that basically solve the problem of not needing all the other filters at different KHZ?  This probably is a stupid question, but would really like to learn.  Mark KB3Z
>