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 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com