[Elecraft] K3: SSB generation

[Wayne Burdick]

Hi Larry,

> The schematics show two internal crystal filters:
> 
> one on the receive path (2 poles) K3 RF Board
> It's marked BW 14 kHz.  8215.0 KHz.
> This has no relay to bypass it.

This is used to further suppress the 2nd-IF image response at 8245 kHz. It has essentially no ripple and thus no negative impact on the passband.


> 
> one on the transmit path (4 poles) KREF3 REF/2ND TX IF
> It's marked 8215.0 kHz, BW=4 kHz
> This has a relay to move to bypass it.

This filter lowers the low noise floor of the IF signal feeding the transmit gain stages and main IF crystal filters. We bypass it in wideband transmit modes (AM, FM, ESSB).

This supplemental filtering is needed to achieve the K3's high blocking dynamic range, rapid fall-off of phase noise, and excellent rejection of image responses.

73,
Wayne
N6KR