Silver soldering copper sheet

[G8HQP Dave]

This not one of those 'Poynting vector synthesis' antennas, is it? If so, be prepared for some degree of disappointment when they try to get it to radiate.

[Silicon]

I googled 'crossed field antenna' and found some images that reminded me of a loudspeaker frame pointing upwards.

The 'loudspeaker' was mounted on vertical rods above a disc.

[Radio Wrangler]

Ah-Ha!

I came across this: "Communications Dynamics Limited (Our new branch company in UK-Isle of Man), is erecting now a directional CFA in JURBY, ISLE OF MAN. This CFA will be in operation by summer 2015, and will be tested by Ofcom." on the webpage of Kabbery Antenna Technology.

David

[G8HQP Dave]

I had a vague memory of seeing a picture of one of those a few years ago (in Egypt?) and it sounded like the description we were just given. I guess this is not the thread to discuss compact antenna design and common misunderstandings.

[G8HQP Dave]

I found the planning permission for the antenna: 5 years temporary approval for tests.

[MotorBikeLes]

Dave, yes, there is one in Egypt, and in fact it is an Egyptian who is (more or less) in charge.
Crossed field antenna. Something new to me. I may look it up later.
Les.

[Radio Wrangler]

What is it?

Let's start from the beginning....

Jame Clark Maxwell, originally from Edinburgh had been studying at Cambridge. He took the equations then used to describe magnetic induction, electric fields and magnetic fields and distilled them all into four little equations. He had been studying some things called 'quaternions' and so he wrote the equations in quaternion form. So they are couched in obscure mathematics rather than the more mainstream sorts. They've been vexing students ever since.

One solution of the equations describes a pair of waves moving along together, each undulating at right angles to the other, and both at right angles to their direction of propagation. One is magnetic, the other electric. Each induces the other, so there is a sort of constant power flow from one to the other, so that after a while there is a steady relationship between their strengths. They are settled into equilibrium with an electric field strength of 377 volts/metre for every amp per metre of the magnetic field strength.

If we divide the 377 volts per metre by the 1 amps per metre, the 'per metre's cancel and leaves us 377 volts per amp. We know another name for volts per amp.... Ohms! So some one called this the impedance of free space, and other people ave been wondering where to stick the avo prods to measure it ever since!

If we multiply the 377 volts per metre by the 1 amp per metre, we get 377 watts per square meter. If we are clever and do a vector multiplication, taking into account the directions of the electric and magnetic fields, then we get a direction in which the power is mocing... the direction of the wave's travel. Watts/sq metre is power density. This multiplication is called the poynting vector afted a chap called poynting. Some people think it's 'pointing'

Most normal antennae are current-based machines and make magnetic field waves.This is OK, because as per Mr Maxwell's equations, after a little while, the mag wave has induced an electric wave and they have settled down into a balanced existence.

Maurice Hately thought it would be a good idea to not simply make one component, but to carefully make both. His "Crossed Field' antennae combine electric field radiating bits as well as mag field radiating bits. On the face of it, it seems like a good idea. If you wanted mature electromagnetic wave-pairs in the closer proximity to an antenna than Maxwell already provided. I could see it being useful for susceptibility testing in small screened rooms. For communications at a distance of more than a dozen wavelengths or so, Maxwell does the job perfectly. Conservation of energy says you don't get anything for nothing, and existing antennae are of known efficiencies. It is difficult to see how the CFA could offer much other than possibly a smaller size.

Maurice's first CFA was a pair of discs located with a separation of maybe 100mm and a couple of metres diameter. and outside of them, two barrel-sized cylindrical electrodes. All four items strung on the same axis.

He connected them up with lengths of RG58 to a 'phasing' box.

The 50 Ohm medium-loss cable would be a terrible mismatch for the impedances offered by either the discs or the barrels, and losses would have been multiplied by the bad reflections whatever the phasing box did. Maurice used to be on the topband net on a weekend, but despite having an Icom 400W PEP semiconductor power amp,he was one of the quieter signals.

the antenna evolved from its balanced form to an asymmetric one using an image reflected in a ground-plane.

So, I haven't bought in to the CFA. Making the whole Poynting vector at once is unnecessary because Maxwell's equations show how asymmetry fixes itself within a couple of dozen microseconds at medium wave. What seems to be lacking is any reason why the E-field and H-field transducers should be smaller than routine antennae.Yer normal halfwave dipole is an H-field transducer of reasonable performance. The fall-off in efficiency if it is shortened and padded out with tuning units is well known. This will apply to making a small H-field transducer in the CFA.

So this is why Dave above expects the results to be a bit underwhelming.

Maurice was offered the opportunity to try the thing out as a test-field generator in a decent sized screened room, but he didn't take it up. If he had, I'd have had near-field measurements, which is where I think the unit might have had something to offer.

David

[Jon_G4MDC]

Very much enjoyed that David, thank you.
Especially the bit about Avo prods

[G8HQP Dave]

So, I haven't bought in to the CFA.

Neither have I. If it appears to work (which I doubt) it certainly won't be because Maurice Hately (GM/G3HAT) was right. He seemed to imagine that the equals sign in Maxwell's equations was some sort of causal link, so writing the equation backwards was a new idea giving new insights. Any physicist or well-taught engineer could have told him (and probably did tell him) that he was mistaken, and the equals sign is simply saying equality; 'his idea' of making a magnetic field from a changing electric field was always known and understood. The fact that some people speak (wrongly) of changing currents as the only means of producing a magnetic field may have sent him off down the wrong path.

What he didn't understand is that the only way to get significant radiation (and hence radiation resistance) is via retardation, which needs distance. Hence all small antennas are subject to the Chu-Wheeler limit, which imposes a restriction on simultaneously having wide bandwidth, high efficiency and small size. All attempts to break this limit are bound to fail, whether the inventor realises this or not.

[MotorBikeLes]

David, a good sounding explanation. (I said "sounding" because who am I to say just "good", that would imply I KNEW.)
It will be between 55 and 60 years ago that at Tech they tried to hammer some of that in, but I managed eight years of study without ever fully "getting it". It was always the abstruse stuff that lost me. Common sense physics was easy, and I can recite most of it today, but not this. I used to meet self imposed blocs. "Consider the unit current carried on two parallel wires of infinite length", was the lecturer's first words. My brain knew that infinitely long wires could only carry infinitely small currents, so the rest of the explanation was irrelevant.
But so much of what you wrote was familiar in so much as I have probably read it all in bits over the previously cited 55 years.
At least I understand the logic behind the crossed field bit, now you have "poynted" it out.
Les.

[Radio Wrangler]

It was when I realised that electrons, photons and all that jazz didn't actually exist that I started to be able to handle physics. SOMETHING exists, but those things with names are human inventions designed as models to sort of fit what has been seen to happen. They have no better justification than that.

Sometimes theoreticians can put their models into interesting circumstances and predict what will happen. If it actually does happen, then the models look useful, if something else happens, the models get revised, or maybe another agent gets invented to explain things. Some areas have begun to look like sticking plasters piled on sticking plasters.

Currently, physicists seem to like particles, and have invented 'carrier' particles for all forces and effects. I'll bet they even have carrier particles for smugness and embarrassment.

(The unit of smugness is the Robinson, named after a sixties quiz show host who appeared to think himself cleverer than the contestants because he had the answers on a sheet of paper. Like the Farad, the Robinson is too large a base unit for everyday application)

You have to apply an infinite voltage to those infinitely long wires to get a finite current to flow.

David

[mole42uk]

According to para 8 of the Planning Application, a similar CFA has been tested in Yorkshire demonstrating its' "exeptional performance". Compared to monopole antennas it requires less power input and lower elevation for a similar performance. Apparently tested and verified by Arquiva.

As they say in America, "Go Figure" - I can't work it out, but someone has because the carrier particle for all this is cold, hard, cash!

[G8HQP Dave]

Originally Posted by Radio_Wrangler

It was when I realised that electrons, photons and all that jazz didn't actually exist that I started to be able to handle physics. SOMETHING exists, but those things with names are human inventions designed as models to sort of fit what has been seen to happen. They have no better justification than that.

On the contrary, it is precisely because such things do exist that models using them are so extraordinarily successful in not only predicting the results of careful experiments but also providing genuine understanding. (Both your view and my view are held by different physicists - naturally I believe that my view is better!)

Some areas have begun to look like sticking plasters piled on sticking plasters.

That I can agree with. It is a sign that our understanding is poor in some areas. When our theory needs no patching up we can be sure we are near the truth - at least at the appropriate level of approximation and abstraction.

Currently, physicists seem to like particles, and have invented 'carrier' particles for all forces and effects. I'll bet they even have carrier particles for smugness and embarrassment.

The universe seems to like quantised fields, which we often see as particles, with symmetries and conservation laws. Our job is to discover what they are. We did have particles carrying Truth and Beauty, but they now have more boring names like top and bottom.

A Google search will find a report on the Yorkshire CFA tests. It no longer appears on the manufacturer's website, but someone seems to have put another copy up. There seems to be an emerging consensus that the CFA works best when elevated on a conductive platform - perhaps the height of the platform contributes to the effective height of the antenna, as the platform vertical supports are likely to be carrying RF currents.

A Google search will find a report on the Yorkshire CFA tests.

Go on, give us a link. A CFA on top of a 'stick' would make a great capacity hat for a vertical making it perform better than a straight (un-hatted) vertical. Has anyone tested a CFA with battery powered energisers at the antenna rather than "matching" via feeders? It's the feeders that make the aerial, not the CFA.

[mole42uk]

http://www.ok1mjo.com/all/ostatni/t-...ort-report.pdf

[G8HQP Dave]

Try http://www.ok1mjo.com/all/ostatni/t-...ort-report.pdf.

The results appear to show that the CFA is slightly better at radiating than an ideal quarter-wave monopole (comparing CFA measurements with monopole calculations, taking account of ground conductivity). I find this hard to believe, as the monopole would be fairly easy to match to 50ohms so matching losses would be small while the CFA would be a pig to match so losses would be higher. Of course, once you actually get the current flowing the radiator losses will be small for both antennas.

One thought: to what extent did the monopole calculation take account of losses in the ground connection which the monopole will need? I believe the CFA does not need a ground connection so will only have ground losses in propagation, not feeding? Comparing measurements of X with calculations for Y is always fraught with comparability issues.

The link is no longer valid, I wonder why?

The second link did, with all that copper in the air compared to a thin vertical I am not surprised it works a weeny bit better than a thin one. I bet it is working as a simple vertical with uncomprehensibl readings on the matching units. The old adage of sticking as much as possible up in the air seems to hold true. Does look pretty, I don't think the neighbours would like it and the wife would soon be growing something up it.

[m0cemdave]

For anyone interested, the test antenna is visible on Google Earth, at 53.935473, -1.931830.
View "historical imagery" and go back to 2009.

Also visible from the road in the somewhat out-of-date Street View.

[Herald1360]

Originally Posted by m0cemdave

Also visible from the road in the somewhat out-of-date Street View.

Looks like Frankenstein's Mushroom!