[Elecraft] K3: KRX3 question

[Don Wilhelm]

David,

In most instances, you are correct.  My K3 has only the stock 2.7 
filter, but then I am not into heavy contesting nor intense DX chasing - 
I do some contesting and work DX for fun only.  When it gets to the 
point where I really need narrow roofing filters, it is time for me to 
go listen to some relaxing music, so you will not find me using 
diversity reception to pull out some obscure weak signal.

One related point - the Hardware AGC should prevent overload of the DSP, 
so the K3 will handle those strong signals nicely.  The problem is that 
the AGC action when a strong unwanted signal is within the roofing 
filter passband, the AGC will reduce the sensitivity of the entire 
receiver, so your wanted signal gets weaker too - and you may not even 
know the offending signal is there if you have the DSP bandwidth at a 
narrow width - it will behave as though there is QSB on the signal you 
are listening to.  Of course using diversity reception with one antenna 
having lower gain, that QSB effect may be minimized.

73,
Don W3FPR

David Cutter wrote:
> I think I must be missing something.
>
> As I understand it, the additional crystal filters are only really 
> necessary when operating with very strong adjacent signals in the 
> passband.  So, if you don't have a need for rejection of such strong 
> signals, let's say >40 over S9 (somebody correct this figure please) 
> then you don't need these extra filters, the DSP will cope with these 
> large signals.  The filters are only there to prevent overload of the 
> DSP.
>
> Therefore, to perform the very best diversity reception in <40 over S9 
> conditions, turn off those extra filters in configuration menu.
>
> Having turned off the filters, I can engage the attenuator to avoid 
> DSP overload if needed.  Yes, I know it also reduces the signal I'm 
> trying to hear, but that sacrifice may be what is needed.
>
> For diversity reception using low gain loop, pennant, flag, Beverage, 
> loaded whip antennas, the signal input is very much lower than from 
> the tx antenna, so, crystal filters are probably not be needed at all.
>
> Or do I have it all completely wrong?
>