[Elecraft] An idea for the K2

[Geoffrey Mackenzie-Kennedy]

I believe that you would be proven correct about the RF feedback.

My thought about a tin box totally enclosing the PCB stems from an
observation that the skirts of the varicap "controlled" filter set for say
700Hz bandwidth are a little wider with the KSB2 installed than when it it
is not, and noticeable from approx 40db below passband on down. I made no
measurements because I was Birdy hunting/killing at the time. If this
blow-by is due to leakage between P2 and P3 or through the switching diodes
(off) on the KSB2, then the tin box would have little if any effect. But the
KSB2 does come close to forming a bypass route just due to its proximity to
the post mixer amp, RF board filter etc, and my gut feeling is that a box
around the KSB2 or its replacement would be a good start. The box would also
help to keep out the RF from nearby oscillators.

73,
Geoff    GM4ESD

On Wed.2nd March 2005, Stewart G3RXQ wrote:

Any form of increasing the mic gain internally (eg rf speech clipper) needs
to
be carefully thought out. The microphone signal routing and earthing from
the
front panel socket thru the RF board and into the KSB2 is far from ideal.
Common mode, series mode - the lot - RF feedback is the likely result.

A groundplane board with the crystal filter laid out to reduce blow-by may
be
the way to go. A tin can over the whole assembly may help. The biggest
hurdle to
overcome in making changes to the KSB2 is interfacing with the existing
firmware
which is far from straightforward.

73
Stewart G3RXQ

On Wed, 2 Mar 2005 08:11:54 -0000, Geoffrey Mackenzie-Kennedy wrote:
> Intersting ideas. If you did enlarge the SSB board to get all the bits in,
>
> in which directions would you enlarge the exixting board?
> IMHO it would be essential to contain the "new" board in a 'tin' box in
turn
> mounted on metal, which raises the question of access to test points etc
on
> the RF board, but a solution might be available.
>