Well, I ran into a road block this afternoon that took some time to sort out. I built the FET VFO and Follower (for isolation) portions of the VFO…but could not get it to oscillate. After checking wiring and voltages, I pulled another 2N4416A from the junk box and checked it with my M-Cubed semiconductor checker. I noticed that it showed the DRAIN and SOURCE pins reversed from what the datasheet indicated. I rebuilt the two stages using the info that the M-Cubed checker showed me and the VFO worked. I got these 2N4416A’s from a reputable USA company but now wonder if maybe they were clones from an overseas location. Bottom line…never assume anything, always check and measure everything.
Have the BUFFER AMP to build and then do some tweaking and final measurements. This project is a joint effort of Todd, VE7BPO and myself for an article for the Michigan QRP Club’s quarterly publication called “The 5 Watter” (T5W). Todd suggested this article during the winter months and it has been a fun adventure so far. I sort of got side tracked this last month and just now am getting back on track with the project. The original 8640-jr project was done by Wes, W7ZOI…it is a three band VFO that develops a 13 to 30 MHz signal which is then ran through a couple of dividers to result in 3.5, 7 and 14 MHz VFO signal source or can be configured to run from 3.4 to 31 MHz as a signal generator.
Always fun to snuff solder fumes and figure out why things don’t work the first time as planned <smile>.
Wb8icn's Blog 
March 31, 2015 at 6:21 pm |
These JFETs are very close to be symmetrical. It seems that the oscillator was close to oscillations and when reversing the JFET, the little difference between the two connection directions was enough to bring it to oscillate.
Victor – 4Z4ME