One antenna coupler.
Here's the making of an antenna coupler for ham radio, for my friend Jacques ON5MJ. Of course, I do only the mecanical assembly and build the stepper motors control unit. The clever high frequency calculations are for him ! :-)
The assembly has two «rolling» coils, moving together, and two variable capacitors, independant from each other. The whole assembly must be fitted on an insulated support. I've choose the electric «carta» , used in high-voltage assemblies. The sheets are 10 millimiters thick, and have a good strenght. It's possible to drilll and tap in the sheets, even in the thickness!
This assembly is made with second-hand material. The motors are coming from old (and very big) printers. One motor will control the two coils (by means of a belt); and two smaller motors will drive the capacitors, with gears.
At this day, (July 31, 2005), the mecanical part is done. The electronic control for the motors is an experiment, just for testing the mecanic.
Clic on the pictures so see it bigger in another window...
The definitive mecanical making. nothing is wired at this moment. I must still place the position detectors, for the zero position of the motors.
The first prototype was using a too small motor for the two coils (you can see on the vertical panel). It was stopping or missing steps, because not strong enough. I've place a really bigger model... I don't have other! :-)
The assembly with the definitive motor.
The other side of the assembly. The belt and the tension system are visible.
The coils axis cannot be driven directly, because the belt mecanical tension is toot strong and can destroy the coils. I add a bearing on each coil axis.
And, to avoid electrical coupling between the coils axis (wich are under RF voltage) and the bearing axis, an insulating part is used. This can also be useful if the two axis are not exactly in the same path.
The variable capacitors are driven by means of plastic gearings...
... for two reasons : to avoid electrical coupling with the motor axis, and also to avoid to transmit the vibrations of the motors to the capacitors. Those capacitors don't need powerful motors.
One of the coils axis bearings.
The two bearings on the vertical panel, at the beginning of the assembly.
The stepper motor command, prototype. The electronic in the aluminium frame is my counter (when i make transformer windings). It's fitted with a multipole plug, to use this counter for other uses without wiring another counters on prototype board. The BCD counters control and output signals are avaliable for other experiences !
This is the stepper motor interface, prototype wired just for the mechanical test. When I use on the big motor, this is heating... a lot ! I have to make something more reliable now. But this elementary electronic wiring has been OK for all the tests !
The schematic of this electronic card has not a great interest, it was only for the tests. But a part of this (the power control) will be re-used for the definitive control unit.