christofire wrote:

A source of endless coffee-time debates where I used to work! No, the
current into the rotating dipole would be DC and the means of rotation at
the radio frequency would take the place of the 'transmitter'. If the
current were alternating then the radiated electric field would be
discontinuous but it isn't; it has constant magnitude. Between two such
systems separated by many wavelengths, if there were no anisotropic material
around, reciprocity would apply and a means of conveying DC by radio would
be created!

Now that I think about it, you're right -- the current would have to be
DC, so there would be only DC power into the dipole.

Interesting that you and your co-workers thought of and debated this.
I've given it less than an hour of thought since it popped into my head,
so you've had a lot more time to work out the details. Sounds like it
might work something like I described, then.

However, intriguing and amusing as this analogy might be I wonder if it
really has any practical value. For real mechanical rotating parts the
frequency would be limited to something rather low like the tens of kHz at
which Alexanderson alternators work, and then the wavelength would be so
long that it would probably be impossible to construct an efficient
radiator*. The quickest moving antenna I've encountered was a commutated
plasma antenna, using a construction similar to a 'dekatron' tube, but even
then the length of the radiator was so small that SHF would be needed to
achieve worthwhile radiation efficiency* and the maximum commutation speed
was limited to a few MHz by the time it takes to establish the plasma at
each step in the commutation cycle.

I can't see where this could possibly be of any practical use. For me it
was simply a mind exercise spurred by Peter's musings, resulting from
wondering just how a mechanical system could be made to generate a CP wave.

*(Of course, the conventional principles of radiation resistance vs. loss
resistance may need 'massaging' to bring them into line with the concept of
creating transverse waves by rotating a dipole connected to a battery!)

Indeed. And it seems there wouldn't be any skin effect, then, with only
DC going to the wire. And what about current distribution on the dipole?

Roy Lewallen, W7EL