[Elecraft] K3 Signal blocking inside of the crystal filter BW

[Lyle Johnson]

Hello Dave!

> When trying to work a station simplex in a pileup I experienced receiver blocking.  While trying to listen to the DX station others were calling so I narrowed the passband down to 200hz.  I was unable to copy the weaker station very well because the louder stations were retarding the AGC...
>
> I found if the DSP is set the same as the 400Hz crystal filter, I have 8 pole, the blocking does not occur.

The basic design of the K3 is to make use of the 1st IF crystal filter 
to narrow the in-band bandwidth to be consistent with the modulation 
method in use.  This is why the K3 can accommodate such a wide range of 
roofing filters and with so many bandwidth options.

The great numbers the K3 has in terms of narrow-spaced dynamic range 
(see for example < URL:http://www.sherweng.com/table.html > are due to 
the use of narrow roofing filters.

To maximize the in-band dynamic range, the sensitivity floor of the 
radio should be set to just below the current band/antenna noise floor. 
  On most bands, the ATTN can be used, adding about 10 dB to the level 
before which the hardware AGC activates.  Most bands do not require the 
use of the PREamplifier, getting another potential gain of 10 dB or so.

73,

Lyle KK7P