Listening on 40 with a Glue Stick PTO in a Direct Conversion Receiver; Some PTO History

Thanks to Paul WA1MAC for this idea.  He first shared it with us via the SolderSmoke mailbag in 2008! Sorry it took so long for me to try one Paul. 

The PTO itself is an old idea of course.  Here is an article from 1966: 

https://www.radioexperimenter.us/rm-1966-04/a-homebrew-permeability-tuned-vfo.html

OM faced the problem of having to keep track of frequency while turning the dial many times.  He was hoping to use a turns counter -- in 1966 we didn't have the San Jian frequency counters.  I note that his PTO looked a lot like the one KK4DAS 3D printed for me (using file from Farhan).  

And some background on PTOs: https://sites.google.com/site/randomwok/Home/electronic-projects/permeability-tuners-last-stand