"Jerry" wrote in message
...

"Roy Lewallen" wrote in message
treetonline...
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

Hi Roy

I have problems with believing there will be any current in either
dipole. What am I missing?

Jerry KD6JDJ


That's understandable.

Chris