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Re: Remote Tuned Primary (RTP) ideas...



Hi Terry,



> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
> One of my new projects (one of a zillion I have planned for the cold
> months ;-)) is to make a remote primary tuning device.  It has two
>parts.

snip

> The second part is more interesting.  Having thought of many "great
>ideas" and having them all disintegrate for various reasons, I have
>settled on the following:  I will have an "extra" MMC with four stings.
>They will have a value of 0.5, 1.0, 2.0, and 4.0nF (could be other
>values too).  This device will be parallel with the regular primary
>cap.  By selecting the strings in a binary fashion, I can select
>from 0nF to 7.5nF of additional capacitance in 0.5nF steps.  Four
> fiber optic cables and simple circuits, as above, will select the
>capacitance from a simple binary thumb wheel switch. Piece
> of cake!  Except for the four actual switching devices.


A few (rough) ideas for the switch:
--------------------------------------------
1.) Use a large stepper relay. Remove a few of the contacts
(to prevent arcing) in between. If you get a large one, it should
not be a problem to prevent them from arcing as you have
a large distance to the next set of contacts, esp. if you remove
two or three contacts. You would need to design a small circuit
that would switch the stepper the appropriate number of steps.
In other words, lets say you have a stepper relay with a total
of 12 contacts (you need four), so you would leave the first set
in place, remove three, leave the fifth one and so on. Your control
circuit would need to "move" the stepper from contact one to
contact five with one push of the button, which means you need a
circuit that makes 4 pulses out of that one that you "contribute"
(when you push the button). Easy enough, I think. As you have
large spacing, you could do away with the oil (mess, fire hazard,
etc).

Disadvantages:
-------------------
a.) Slightly complex
b.) Needs workmanship
c.) Must RF resistant
d.) Involves electronics around HV (shielding, grounding, etc)
e.) You can only switch in "predefined" capacitance steps

2.) A stepper (via a gearbox maybe) driven disk or beam with
two electrodes on the outside. Mount eight stationary electrodes
in a circle around the beam. Each "switch" uses two of these
electrodes. Your control circuit needs to give a predefined number
of steps, so that the beam or disc switches to the next position.
This shouldnīt be too hard for a stepper motor, tho.

Disadvantages:
-------------------
a.) same as above plus,
b.) you will have losses, as you arenīt really making direct
contact (there will always be a small gap).


3.) Make your own HV relay. Using four solenoids to make four
individual switches. You will need to insulate the plunger body
(metal rod) from the switch head, which obviously must be made
out of metal with a plastic rod in between the two. The (lower)
head is one contact and the drop plate is the second contact. You
will need to solder some thick silver braid to the plunger head, so
that you can make the electrical contact to the head. With a powerful
and long length solenoid you can make and break the contact to
the caps w/o having to fear an electrical flame while switching.
The machine work is easy and fast to do. You donīt need any sort
of *real* electronics. Four simple opto-isolated power switch for the
solenoids would do the trick. Biggest advantage: you can switch the
caps in any combo you like (from no additional capacitance to all
capacitance in).

Just some ideas. Letīs see what others come up with ;o) However,
I would defiantly stay away from any kind of "oil-based" solution to
avoid mess, hassle (esp if you will be transporting this) and the
always present fire hazard.

Coiler greets from Germany,
Reinhard


P.S.: Lately, I have been receiving some mails twice. Last example
was HDNīs mail about the "Binary Resonant Tesla Coil". One has
a time stamp 12:09 and the second (yet identical mail) has a time
stamp from 12:33. Just thought Iīd let you know ;o)

<<<< I slipped up and accidently sent it twice :o) - Terry >>>>