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Re: Tesla Coil RF Transmitter



Original poster: "Gary Peterson" <gary@xxxxxxxxxxxx>


Original poster: Ed Phillips <evp@xxxxxxxxxxx>

. . . What is it you believe?  Do you believe he succeeded in making a device
with NO capacitance?  "I have invented such an instrument and have
demonstrated its efficacy."


It appears that Tesla was referring a vacuum-tube device for the detection of weak electrical signals mentioned in the original patent application for the 1898 U.S. Patent METHOD AND APPARATUS FOR CONTROLLING MECHANISM OF MOVING VESSEL OR VEHICLES;

". . . the by far most sensitive device of this kind of which I have knowledge, is a form of luminous discharge which is produced in an exhausted globe under peculiar conditions described by me, and which I have designated as the rotating brush. This discharge is affected by the minutest variations of electrostatic potential or magnetic condition of bodies in its vicinity and may be utilized in a number of ways, as will easily suggest themselves to electricians, for the purpose here contemplated. . . ."

As can be seen from a comparison with the as-issued patent, some problem was found with this particular specification and it was removed.

It appears that Tesla used his rotating brush detector in conjunction with a helical-resonator receiving circuit to create his "ideal receiver." He starts with his receiving transformer and then removes the "fourth circuit" or secondary, leaving just the elevated terminal and the ground connection. The coupling between the receiver's resonator circuit and the rotating brush detector is by electrostatic induction only, taking advantage of the small e-field the transmitted energy creates in the immediate vicinity of the resonator. Keep in mind that he said the secondary of the receiving transformer had been removed. That's the reason he says there is no "capacity current."

As for the practical application of this principle as it relates to this discussion, Tesla's rotating brush tube was improved upon by Lee de Forest resulting in the Audion triode detector. Now we have even more sensitive detectors such as the solid-state MOSFET that can be used in the exact same way as Tesla's original device.

Ed

Gary