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New twist on the bandwidth problem


#1

Here’s something for the technically minded amongst us - OK, I’ll get my coat…

http://discovermagazine.com/2011/oct/13-twisting-radio-waves-100x-more-wireless-bandwidth

“The idea is to twist radio waves like corkscrews and create multiple subfrequencies, distinguished by their degree of twistedness. (Note this type of wave-twisting is fundamentally different from the better-known circular polarization of light.)”. Uh huh…

73, Rob DM1CM


#2

In reply to DM1CM:

Their black holes paper is theoretical - they haven’t observed this effect, they’ve said their theory says it should happen.

As far as I’m aware, their “demonstration” paper is submitted but not yet published (i.e. still going through peer review). There was some correspondence on this in the RSGB’s “RadCom” magazine. The demonstration sounded like hype set up for the media (scientists need to attract attention to get funding from anywhere they can get it!). I’m very suspicious of these young whipper-snappers these days!

Waves stick and falls back into bath chair …

73
John GM8OTI


#3

In reply to GM8OTI:

Well (adjusts prosthetics), according to the paper http://arxiv.org/pdf/1101.6015v1 they’ve actually been there, done it and have at least ordered the T-shirts: “…we used a single antenna and reflector to directly generate twisted radio beams and verified that their topological properties agree with theoretical predictions.”.

So, in next to no time we’ll be marching up the hills with helical arrays for 40m. Me, I’ll be ordering the newest edition of “Slothing for Dummies” any day soon…

Rob DM1CM


#4

In reply to DM1CM:

Sounds much like VMSK and other such bunkum.

Andy
MM0FMF


#5

In reply to MM0FMF:

I bet you don’t believe in Father Christmas either…

Rob
DM1CM


#6

In reply to DM1CM and MM0FMF:

Well I thought I’d put my computer reading glasses on and have a further dig. This

http://www.physics.irfu.se/Publications/Presentations/ThideEtTamburini:Bristol:2011.pdf

is a presentation which is certainly interesting - especially as the idea clearly goes back to 1949!

What is also interesting is that the idea has been rattling around for some years (e.g. a DARPA call for funding in 2009) clearly without much result as of yet. That’s probably why they’ve been toting their seminar around and trying to get the media interested - they clearly think they’re on to something.

I can’t see an instant obvious riposte to their ideas, but in the back of my mind is the memory that photons at radio frequencies are great big soggy things (coherence length and so on) and that that might not help them. However we shall no doubt see in the fullness of time, with the inexorable passing of the years …

73
John GM8OTI


#7

In reply to GM8OTI:

Quote:
"What is also interesting is that the idea has been rattling around for some years (e.g. a DARPA call for funding in 2009) clearly without much result as of yet. "

They can’t be that bright as scientists - if they just included the phrase “climate change” or “global warming” the funding will just flood in!

Barry GM4TOE


#8

In reply to GM4TOE:

They can’t be that bright as scientists - if they just included the
phrase “climate change” or “global warming” the
funding will just flood in!

Barry GM4TOE

And rightly so!

73

Brian G8ADD


#9

In reply to G8ADD:

And rightly so!

Wicked! It’s like being poked with a stick! :wink:

73
John GM8OTI


#10

Have been observing this effect on 23cms for a while. Using variable speed egg whisks for antennas. The main problem is the receiving station needs to have their antenna spinning in the opposite direction to the transmitting station. The whisk speeds need to be exactly the same and stable. Matching speed is done by one station picking a speed and transmitting a carrier while the other station tunes ‘Fast to slow’. Portable operation and outside antennas do not work very well due to what we call ‘Flutter’ which is induced in our spinning antennas by variation in wind speed.

Is it April yet and how do we increase the number of amateurs by a factor of 100?

73 Steve GW7AAV


#11

In reply to GW7AAV:

their antenna spinning in the opposite direction to the transmitting station.

That would introduce maximum polarisation loss wouldn’t it?

Andy
MM0FMF


#12

In reply to MM0FMF:

In reply to GW7AAV:

their antenna spinning in the opposite direction to the
transmitting station.

That would introduce maximum polarisation loss wouldn’t it?

Andy
MM0FMF

No! Spinning in opposite directions keeps the antennas in phase. Spinning in the same direction causes signal compression with an effect similar to Doppler shift. It is all explained in my paper, entitled ‘How Dragons Fly and Other Dodgy Science’.

Steve GW7AAV :0)


#13

In reply to GW7AAV:
Nice one Steve, liking the last few posts. Any thoughts on the Higgs boson from your dodgy science papers?

Adrian


#14

In reply to MM0TAI:

‘We don’t serve your kind in here’ said the barman!

Two faster than light neutrinos walked into a bar.

:slight_smile:

Andy, MM0FMF
(having a Christmas curry)


#15

In reply to MM0TAI:

In reply to GW7AAV:
Any thoughts on the Higgs boson from your dodgy science papers?

Not specifically but my experiments prove that bad news travels faster than light and I am fairly convinced that light travels faster than light when it wants to, sometimes so fast it explodes in a small puff of smoke. This effect can often be observed using a carbon filament in a gas filled glass tube and switching the current on and off rapidly.

Maybe the so called big bang was caused when two particle/waves (Higgs?) bumped in to each other while whizzing through space which proves that either light and related particle/waves do not travel in straight lines or space is shaped like a doughnut, because otherwise they would keep on going forever in the form of parallel lines. Only a head on collision will do because any tangential impact would not have the force require to create mass from energy, ie twice the speed of light.

My next experiments will probably involve inverse light using what I call the ‘Light Reversing Diode’ or LRD for short. This is of particular interest to me as a shift worker as I will be able to flood a room with darkness when I am in bed during the day.

Steve GW7AAV


#16

In reply to GW7AAV:

In reply to MM0TAI:

My next experiments will probably involve inverse light using what I
call the ‘Light Reversing Diode’ or LRD for short.

I might take a few of the LRD’s off you Steve, and develop some from of light cancelling device, and make it look like a regular bulb that you would plug in to a standard light socket and use similar technology to noise cancelling headphones, to amplify the inverted lighting signal to make a really dark room.

We will make millions of £’s Steve :slight_smile:

Adrian
MM0TAI


#17

Actually this is all correct scientifically, although nothing good comes of trying to sell ideas to the media in the way they are doing it.

These ideas have indeed been around for a long time and I knew some of the people in the 1990s that were developing the theory and the experiments for light. More commonly then they were known as Laguerre-Gaussian beams after the mathematical functions they are based on.

The only difference from normal light is these beams have a helical wavefront with a phase jump and n complete rotations for each wavelength propagated if they possess n units of angular momentum. If you look at some of the articles for the RF work they just use a dish which has been warped so that it is in the shape of a spiral; this leads to a shift in the phase that is a spiral and the split is the phase jump. For the light experiments it is more common to use a holigraphic plate with a phase discontinuity since it is harder to impart phase directly as the wavelength gets shorter.

Note, however, that in the RF experiments they only use one unit of angular momentum. There is a reason for this… the more angular momentum you impart the more the beam diverges. That is the main issue. It was long suggested using multiple beams with different angular momenta in light communications but as you increase the number of bands it becomes harder; for the higher bands the beams diverge and noise becomes an issue.

Note also that the basic concept requires the paraxial approximation, i.e. a beam, not just RF going out at all perpendicular angles like you get with a dipole. Hence why they are operating with microwaves where a beam is more natural since you can use a dish.

So, nothing wrong with the science, but maybe a bit too much hype,

Helen
M0YHB