I can only guess, but the loose standoffs plus the bottom cover were
likely providing a path for the VCO and the BFO to couple together - the
frequencies are close together on 40 meters.
73,
Don W3FPR
On 7/31/2025 8:38 AM, Michael Carter via Elecraft wrote:
Thanks, Don, for clarifying the board structure on the K2. You noted that the
top and bottom covers need not be installed for the radio to still work
properly, and that is my recollection from repeated forays into my K2 for
module additions, etc.
So, going back to the original poster's (Wolfgang) observation that the two
loose standoffs, after tightening and addition of the top-side lockwashers
under the screw heads, appeared to be the cause of the transient distorted
audio he experienced, what might be the cause of the distortion? Depending on
the relative return current path impedances, there will be different amounts of
current flowing in the return traces and broad area copper on the board itself
if the board 'ground plane' is not electrically attached to the case metal
directly under the standoffs. Yet since the radio works perfectly fine without
the covers attached, this suggests that the portion of the return currents
flowing in the case metal is not at issue?
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