Re: [K3] Unanswered Questions ...
Posted by
KK7P on
Oct 25, 2007; 1:00am
URL: http://elecraft.85.s1.nabble.com/K3-Unanswered-Questions-tp455050p455053.html
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
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