Archive for the ‘8640-jr’ Category

8640-jr Final

April 2, 2015

Well, I had it wrong…the pin-outs were as the datasheets showed. But I had to actually draw a picture of the device (both top and bottom view) to convince myself of what I was seeing. Long story short, it works as it should and I am happy with the results.

Here is a pic of the PCB of the VFO and a pic of the output from T1 on my scope.


T1 Output


The power out at 13 MHz is 640 mv peak to peak and 412 mv at 32 MHz. I was surprised that the second harmonic was way down in the noise floor, barely noticeable.

Again, this as part of a project that Todd, VE7BPO proposed back in the winter months as a two part article for the Michigan QRP Club’s quarterly publication called the T5W. Todd did the first article that featured the divider portion of the project that follows this VFO. In a nutshell, the VFO produces a signal source from 13 to 31 MHz. The 20 meter segment is analog and the 40 and 80 meters segments are produced by the digital portions of the project by dividing the analog signal by two and four respectively.

This project was originally conceived by Wes, W7ZOI…and reproduced my many others to follow him.  Though this project falls short in producing a lab grade signal generator, it does provide a great signal source for 3.5 to 30 MHz and can come in handy in the shack and on the workbench.  My thanks to Todd for suggesting this project…I learned a lot and had a lot of fun getting there!




8640-jr Update #1

March 30, 2015

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>.

8640-jr VFO

March 29, 2015

Started assembling a 8640-jr VFO tonight. Should have done this a month ago but been rather busy with no-related bench stuff lately. Built and tested the +6 volt strip and now onto the oscillator and buffer stages.

Located and sorted the parts for the entire project…now just need to build it, then test and measure the three stages. This is for a T5W article that VE7BPO inspired a couple of months ago.