It may have been this one.
![Image](https://people.ohio.edu/postr/bapix/DX60work.jpg)
I'm guessing the variable cap's physical range was mechanically limited so that only the most linear part of its travel was used to tune across a band. Otherwise, the dial calibration at one end of the band or the other might be "squished." Some old, cheaper AM broadcast radio dials often showed the upper AM band frequencies all packed together and lower ones spread apart. A trimmer capacitor could be incorporated to do some "stretching out" and linearize the calibration. A big selling point of Collins and some other high-end ham and commercial gear was a PTO (Permeability Tuned Oscillator), which used a geared drive to push or pull a ferrite or iron core in and out of a coil form, a system which provided nearly perfect linearity. Heathkit later had an "LMO" (Linear Master Oscillator), which achieved a similar result.
The "linear dial calibration " either had specially designed variavle cap plate shaping or used a tuning system that moved slugs in and out of coils.SolarMax wrote: ↑Tue Aug 25, 2020 4:08 pmI'm guessing the variable cap's physical range was mechanically limited so that only the most linear part of its travel was used to tune across a band. Otherwise, the dial calibration at one end of the band or the other might be "squished." Some old, cheaper AM broadcast radio dials often showed the upper AM band frequencies all packed together and lower ones spread apart. A trimmer capacitor could be incorporated to do some "stretching out" and linearize the calibration. A big selling point of Collins and some other high-end ham and commercial gear was a PTO (Permeability Tuned Oscillator), which used a geared drive to push or pull a ferrite or iron core in and out of a coil form, a system which provided nearly perfect linearity. Heathkit later had an "LMO" (Linear Master Oscillator), which achieved a similar result.
I think many of the lightbulb antennas used consist of a Quarter wave of wire attached between the antenna matching tuner and the light.SolarMax wrote: ↑Mon Aug 24, 2020 11:48 pmWe know that a light bulb does radiate,
Unfortunately we've just missed the annual "Light Bulb QSO Party" this past weekend (8/22-23), the purpose of which is to build and use an antenna constructed with a lightbulb as a key component ... and to promote understanding and practical application of antenna matching concepts that allow a lightbulb to be used as a radiator in two way radio communications.
Info on that event and how to start getting ready for the 2021 event at https://hamsignal.com/blog/lightbulb-qso-party-2020