[Elecraft] [K1] Internal Noise Bursts every 12 seconds or so

[Mike Morrow]

Bob wrote:

> In looking over the Front Panel Schematic quickly, my attention was
> drawn to the 6 volt power supply generated on the Front Panel ("6A")
> and distributed to several high gain parts of the RF board.  Any noise
> on 6A is going to be an issue.  I also noted that there is no traditional
> bulk storage cap on the input of the 78L06 regulator, U4, typically .3 to 10
> uF, and while there are a few decoupling caps on the output, the closest one
> to U4 is several inches away C5.  The output cap on a 78L series regulator
> is typically 0.1uF mounted as close to possible.  Finally the original
> specified regulator has been obsoleted and a different unit was substituted.

I wrote previously:

>> It's a long shot, but you may want to check the installation of the
>> similar capacitors on the Display PCB (C4) and KFL1-2 (C27).

I would look closely on the Front Panel PCB (whicn I erroneously called the Display PCB above) at C4 (0.047 uF) on the 6A line to U1 pin 1 and 11.  It of course is on the output of regulator U4.  It would be interesting to see what happens to the noise if a similar cap was installed in parallel with C4.

Mike / KK5F