Discussion in 'General Technical Questions and Answers' started by KC0QWE, Oct 10, 2019.
Kudos and a tip of the hat. I like the way you think.
No, it used to be keyed, but I have made a few improvements since then.
I have removed a switch box that was being used to switch the keyer between a practice oscillator and the transmitter. That, and letting the VFO warm up, with the oscillator on, for 30 minutes seems to have fixed it. I was not able to reproduce the problem again with the straight key or knife switch. The Heathkit keyer did it until I removed the switch box. I still think there's another shoe waiting to drop, though. Probably I knocked something loose. Time will tell. Thanks everyone.
PS the PTO/VFO was not homebrewed by me. It's a kit from W6AOTP. I am very pleased with it. I used a lightweight aluminum project box, and lately it has been drifting a lot. Insulation, shortening component leads, and warm-up time helped. I also added a tiny 1 watt bulb inside the enclosure to help stabilize temperature.
Photo from designer's website.
It appears the designer prioritized small footprint of the VFO board. Standing components on end, resulting in long leads parallel to one another so they can couple with adjacent components is probably not the best choice in an oscillator.
Further, the Manhattan style islands probably doesn't provide good isolation. A better choice would probably be to use a standard two sided board with the underside as the Groundplane, and enlarge the board so that components can be installed in through-hole configuration with minimal lead length.
If size was a critical consideration, then SMD components would be best (Yes, you can solder them with a pen at home!).
Finally, for best mechanical stability the clear plastic coil form should be supported mechanically at the far end from the vertical panel. We tend to gloss over mechanical stability these days, but that is the reason why boat anchors tended to be built with heavy chassis and cases.
"Lately"? I'm curious how long you've been using it. I'm also curious if it was rock, more, or just reasonably stabile prior to "lately."
This leads me to suspect a crapacitor (spelling intentional) needs replacement. Something "has changed." If the output level has changed since "lately", a resister may have changed value, which could also affect stability.
I wonder, what about those jack sockets, if there connections are not 100% they too would cause problems, especially if oxidized the connections will have resistance to any current flowing through them connections.