Circular polarization... does it have to be synchronous??
 

"Roy Lewallen" wrote in message
...
Jerry wrote:

I am not smart enough to analyze the effects of rotating a dipole with
DC applied to it, but I have doubts that it would create a "far field".
Did you guys ever figure out how the "DC dipole" generates a Far Field?

Jerry KD6JDJ

It requires energy to create a far field, since the far field is a form of
energy. I explained why I thought power might be consumed by the
antenna -- current would flow due to coupling with the field still present
from previous positions (although I mentioned alternating current while
Chris correctly pointed out that it would have to be DC). I don't see any
problem with conversion of the DC into AC. It's done all the time with
spinning magnets -- look at the alternator in your car for example. And in
times of yore, RF was generated directly with high speed alternators. The
principle is very similar to, if not exactly the same as, the scheme I
described.

The whole thing is just a mental exercise to help gain a better
understanding of the nature of a circularly polarized field.

Roy Lewallen, W7EL

Hi Roy

When you write "current would flow due to coupling with the field still
present from previous positions", do you submit that more power is required
to rotate a dipole with no DC on it than one with DC on it?

I will respectfully submit that a car alternator doesnt so much spin a
magmetic field as it Rotates the field past a conductor. A car alternator
is a lumpy magnetic field that is spun past stationary coils of wire. There
is no misunderstanding about inductive coupling of close by conductors. My
question related to far field "radiation". I am aware that my understanding
of far Field radiation is very limited, so i dont propose that i have
answers. I do have question about generating a far field by spinning a DC
excited dipole.

Jerry KD6JDJ

Circular polarization... does it have to be synchronous??
 

"christofire" wrote in message
...

"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

Hi Chris

Tell me, did you guys ever decide that there would be a far field
generated by the spinning dipole with DC on it? I dont refer to the
inductive field.
Maybe there is no way to separate Far Field from any condition where an
inductive field is generated.

Jerry KD6JDJ

Circular polarization... does it have to be synchronous??
 

"Jerry" wrote in message
...

- snip -


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

Jerry KD6JDJ


That's understandable.

Chris

Hi Chris

Tell me, did you guys ever decide that there would be a far field
generated by the spinning dipole with DC on it? I dont refer to the
inductive field.
Maybe there is no way to separate Far Field from any condition where an
inductive field is generated.

Jerry KD6JDJ


Jerry,

I think you're right - in the far field there is spherical spreading of
power without regard to separate magnetic and electric components that an
antenna, of whatever form, might produce. Of course the radiated power
incident on any surface can be represented by an equivalent value of
electric or magnetic field strength but this is on strict understanding that
the counterpart (magnetic or electric) component is present with the
requisite field strength (E/H = Zo = 377 ohms in free space) and PFD =
E2/Zo.

The answer to your first question is 'yes - hypothetically' there 'would be
a far field generated by the spinning dipole with DC on it' but this
shouldn't be taken as a recipe for some wacky rotating machine. As I
outlined earlier, there is probably little practical application for this
interesting analogy because if it were ever put into practice it would
probably be hopelessly inefficient and transformation of Maxwell's equations
into an inertial frame spinning at the radio frequency is hard, to say the
least! As has been suggested, it's probably best to take the concept no
further than an interesting thought exercise - if you don't understand that,
don't worry, you're not missing much

Chris

Circular polarization... does it have to be synchronous??
 

"christofire" wrote in message
...

"Jerry" wrote in message
...

- snip -


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

Jerry KD6JDJ


That's understandable.

Chris

Hi Chris

Tell me, did you guys ever decide that there would be a far field
generated by the spinning dipole with DC on it? I dont refer to the
inductive field.
Maybe there is no way to separate Far Field from any condition where an
inductive field is generated.

Jerry KD6JDJ


Jerry,

I think you're right - in the far field there is spherical spreading of
power without regard to separate magnetic and electric components that an
antenna, of whatever form, might produce. Of course the radiated power
incident on any surface can be represented by an equivalent value of
electric or magnetic field strength but this is on strict understanding
that the counterpart (magnetic or electric) component is present with the
requisite field strength (E/H = Zo = 377 ohms in free space) and PFD =
E2/Zo.

The answer to your first question is 'yes - hypothetically' there 'would
be a far field generated by the spinning dipole with DC on it' but this
shouldn't be taken as a recipe for some wacky rotating machine. As I
outlined earlier, there is probably little practical application for this
interesting analogy because if it were ever put into practice it would
probably be hopelessly inefficient and transformation of Maxwell's
equations into an inertial frame spinning at the radio frequency is hard,
to say the least! As has been suggested, it's probably best to take the
concept no further than an interesting thought exercise - if you don't
understand that, don't worry, you're not missing much

Chris

Hi Chris

Thanks for the reply.

Yeah, I never ascribed any practical use to the "CP by spinning". But,
there are some fundamentally good thoughts generated here. For instance, I
can easily see why two dipoles rotating at the same rate and rotational
direction will couple *nothing*. Thats like trying to receive RHCP with a
LHCP antenna.
I have lived a long time without understanding Poynting and Maxwell
(almost 100 years older than me), I wouldnt want to change that now.

Jerry KD6JDJ

Circular polarization... does it have to be synchronous??
 

Richard Clark wrote:

Ærthur, while rooting in the library stacks of an ancient university
located on the banks of a great (but not grand) lake,

That would be good old Miskatonic U in Arkham?

- 73 d eMike N3LI -

Circular polarization... does it have to be synchronous??
 

"christofire" wrote in message
...

"Jerry" wrote in message
...

- snip -


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

Jerry KD6JDJ


That's understandable.

Chris

Hi Chris

Tell me, did you guys ever decide that there would be a far field
generated by the spinning dipole with DC on it? I dont refer to the
inductive field.
Maybe there is no way to separate Far Field from any condition where an
inductive field is generated.

Jerry KD6JDJ


Jerry,

I think you're right - in the far field there is spherical spreading of
power without regard to separate magnetic and electric components that an
antenna, of whatever form, might produce. Of course the radiated power
incident on any surface can be represented by an equivalent value of
electric or magnetic field strength but this is on strict understanding
that the counterpart (magnetic or electric) component is present with the
requisite field strength (E/H = Zo = 377 ohms in free space) and PFD =
E2/Zo.

The answer to your first question is 'yes - hypothetically' there 'would
be a far field generated by the spinning dipole with DC on it' but this
shouldn't be taken as a recipe for some wacky rotating machine. As I
outlined earlier, there is probably little practical application for this
interesting analogy because if it were ever put into practice it would
probably be hopelessly inefficient and transformation of Maxwell's
equations into an inertial frame spinning at the radio frequency is hard,
to say the least! As has been suggested, it's probably best to take the
concept no further than an interesting thought exercise - if you don't
understand that, don't worry, you're not missing much

Chris

Hi Chris

I am having a block in my learning. As I understand it, this would
actually happen if it could be performed.

A spinning dipole would require more power to spin it if it had DC on it
than if it had no DC on it. And, actually, it would require no power to
keep the dipole spinning since there would be that theoritical vacuum around
it. But, once you apply the DC, power would be required to keep it
spinning. That amount of added power would be determined by the amount of
DC applied. Do you confirm that this is true?
My question relates to my ignorance about what there is in the "vacuum" to
cause "drag".

Jerry KD6JDJ

Circular polarization... does it have to be synchronous??
 

"Jerry" wrote in message
...

- snip -

I am having a block in my learning. As I understand it, this would
actually happen if it could be performed.

Yes


A spinning dipole would require more power to spin it if it had DC on it
than if it had no DC on it.

Yes - as I said, the means of spinning the dipole would be the counterpart
to the 'transmitter'

And, actually, it would require no power to keep the dipole spinning since
there would be that theoritical vacuum around it.

If you say so - you're specifying a hypothetical zero-friction system which
is but one of several possible scenarios.

But, once you apply the DC, power would be required to keep it spinning.
That amount of added power would be determined by the amount of DC
applied. Do you confirm that this is true?

Certainly work would need to be done to spin the dipole and create the
outgoing wave by virtue of its rotation. I suppose it follows that the
strength of the outgoing wave would be proportional to the applied voltage
but I'm not certain that a greater voltage would require more mechanical
work to spin the dipole - you may be right but I'm not certain I can confirm
this from what I think I know!

My question relates to my ignorance about what there is in the "vacuum"
to cause "drag".

Jerry KD6JDJ

I'm afraid I had taken very little account of causes of mechanical drag. As
noted before, this was a thought experiment - the sort of thing that can
reach a useful conclusion (i.e. 'not likely' in this case!) without
requiring detailed examination of what may be 'second-order' influences.

Chris

Circular polarization... does it have to be synchronous??
 

-almighty snip-


My question relates to my ignorance about what there is in the "vacuum"
to cause "drag".

Jerry KD6JDJ

Just research 'solar sailing' if you want to read about a phenomenon that
involves 'drag' in a vacuum on account of a flux of photons. It's used to
help keep satellites 'on station' whilst saving hydrazine.

Chris

Circular polarization... does it have to be synchronous??
 

"christofire" wrote in message
...

"Jerry" wrote in message
...

- snip -

I am having a block in my learning. As I understand it, this would
actually happen if it could be performed.

Yes


A spinning dipole would require more power to spin it if it had DC on it
than if it had no DC on it.

Yes - as I said, the means of spinning the dipole would be the counterpart
to the 'transmitter'

And, actually, it would require no power to keep the dipole spinning
since there would be that theoritical vacuum around it.

If you say so - you're specifying a hypothetical zero-friction system
which is but one of several possible scenarios.

But, once you apply the DC, power would be required to keep it spinning.
That amount of added power would be determined by the amount of DC
applied. Do you confirm that this is true?

Certainly work would need to be done to spin the dipole and create the
outgoing wave by virtue of its rotation. I suppose it follows that the
strength of the outgoing wave would be proportional to the applied voltage
but I'm not certain that a greater voltage would require more mechanical
work to spin the dipole - you may be right but I'm not certain I can
confirm this from what I think I know!

My question relates to my ignorance about what there is in the "vacuum"
to cause "drag".

Jerry KD6JDJ

I'm afraid I had taken very little account of causes of mechanical drag.
As noted before, this was a thought experiment - the sort of thing that
can reach a useful conclusion (i.e. 'not likely' in this case!) without
requiring detailed examination of what may be 'second-order' influences.

Chris

Hi Chris

I accept as valid, your statement that the dipole with DC will radiate a
far field when spun. I have a mental block related to questioning what
makes it harder to spin when the DC is increased.
Yes, I do consider the media in which the dipole is spinning creates no
friction. I do wonder what makes it harder to spin when the DC voltage is
increased.

Jerry

Circular polarization... does it have to be synchronous??
 

Hmmm... never been there???

-- Pete K1PO


"Michael Coslo" wrote in message
...
Richard Clark wrote:

Ærthur, while rooting in the library stacks of an ancient university
located on the banks of a great (but not grand) lake,

That would be good old Miskatonic U in Arkham?

- 73 d eMike N3LI -