[Elecraft] [K3] Unanswered Questions ...

[Lyle Johnson]

Hello Joe!

Unlike most DSP-based radios, the K3 converts from the main IF (8.215 
MHz) to the 15 kHz DSP IF without an intervening 455 kHz IF.  This helps 
give the K3 a cleaner sound and better dynamic range since there are 
fewer conversions.

However, this also means the IF crystal filter must have exceptional 
skirt selectivity to prevent the 15 kHz "image" from getting through.

In FM mode, capture effect helps suppress the effect of "image" leakage. 
  AM and (E)SSB modes have far more dynamic range and the 15 kHz IF 
image must be suppressed by some 10s of dB more than is required for 
excellent FM operation.

It is for this reason that the FM filter is recommended only for FM use. 
  It may also be used for AM receive, but is not recommended for AM 
transmit.  The 6 kHz filter has the necessary 15 kHz IF image rejection 
to be suitable for use with either AM or (E)SSB.

73,

Lyle KK7P