I have been an amateur radio operator for very many years and have always been interested in the "Black Art" of antenna's.
Last weekend, a local station operator called me over to try and help with re-erecting his mast. He had a 40ft wind up telescopic mast topped off with a tri band 5 element beam on a large rotator.
We soon had it up and reconnected with new ground plane spikes and coax cable, but when he tried it, the SWR was all over the place and performance was non existent.
We checked everything we could reach to no avail, and reluctantly lowered it all again and I started to examine the antenna. It was only then that he explained that he had taken it down to check for corrosion, and having found some, he had all the elements anodised. The elements are held together with jubilee clips where they are inserted into the traps, but because anodising aluminium makes it non-conductive, there was no connection between the sections.
I was not happy to drill through the tubes and bolt it up for two reasons,
1) I have seen elements crack at bolt holes due to flexing in strong winds,
2) The effective connection point where the bolt is placed, would have to be back from the end of the traps tube and would be in the wrong place for correct tuning. Should the anodising wear through at the end of the trap, it could alter the tuned length of the element.
Have you ever tried to remove anodising with worn out wet and dry abrasive paper? Inside the ends of the large section wasn't too hard, but the small ones were a nightmare.
So, 5 hours later in the wind and rain and in the dark we wound it up again and this time it worked perfectly. Now I have a stinking cold, and spent two days in bed!!! All good fun though, how we suffer for our hobbies!
P.S. he just rang me and said thanks, I told him about the cold and he's promised to send me round a bottle of wine and some paracetamol.

 

That's what hams are all about, being a helping hand to a good ol' buddy in the wind and rain with nary a complaint!

 

Sad case of good intentions gone bad. Hope the cold gets better soon.

The "Black Art/Magic" of RF or antennas? It's all a mater of simple conductor geometry once you really understand how electrical energy moves in space as fields in concert with the elements as wave guides. I've setup and used HF radio links over thousands of miles with only wire-rope as the antenna element using a proper transmit tuner/coupler and top of the line era receivers. The equipment was the easy part, keeping ahead of atmospheric propagation conditions over a long period by moving frequencies or physical antenna locations separates the Professional Radiomen from the boys.

 

The "black art" I refer to, is because the exact same set up in a different location can have completely different performance, without taking into account the atmospheric and sunspot variations.
I meant it in the context of what works best for a given location setting and the financial constraints of the average AMATEUR operator.
It's a whole different ball game when a professional organisation has sufficient funds to overcome many of the problems encountered when doing it on a shoe string.
In fact, I took the phrase "Black art" from an old ARRL antenna handbook I had many years ago.
I agree that a long wire sometimes may be better in some circumstance, but I have a full size G5RV used as an inverted V with the ability to change the configuration to a sloper. My long wire and beam are often outperformed by it in certain conditions, other times, working the same regular stations, it can be the other way around.
If you are lucky enough to live in a decent location, then the performance could well be more consistent albeit with all the vagaries of the prevailing propagation conditions.
We are on the side of a hill where the underlying rock is chalk covered in varying levels of soil, surrounded by huge oak trees. so weather conditions affect the soil conductivity making ground planes very difficult to keep consistent, and the effects of the trees from summer and winter again make a huge difference.
I agree with the ARRL, PRACTICAL amateur radio antennas are not just an exact science, but a source of great experimentation and sometimes frustration in finding a system that is a good compromise for a given set of constraints.

 

The "black art" I refer to, is because the exact same set up in a different location can have completely different performance, without taking into account the atmospheric and sunspot variations.
I meant it in the context of what works best for a given location setting and the financial constraints of the average AMATEUR operator.
It's a whole different ball game when a professional organisation has sufficient funds to overcome many of the problems encountered when doing it on a shoe string.
In fact, I took the phrase "Black art" from an old ARRL antenna handbook I had many years ago.

Sure. I don't like the term "Black art" in the electrical context. It's usually a "Black art" because traditional electronics and electrical education devotes little energy into developing a field view of electronics and electricity in general so action at a distance forces seem 'magical'.

 

Sure. I don't like the term "Black art" in the electrical context. It's usually a "Black art" because traditional electronics and electrical education devotes little energy into developing a field view of electronics and electricity in general so action at a distance forces seem 'magical'.

Ah, yes, I take your point, If the experimentation was conducted with no real knowledge of the subject, any result that suddenly worked better by chance, would indeed be seen that way.
The context in which the ARRL and I were using it, was meant that despite applying the best available practice based on good understanding seemed not to perform as expected, then it is the non-electrical (although they still are in many ways) that need experimentation in the set up to site/reposition if possible or make changes that can by applying practical experience often lead to a more satisfactory outcome. Whilst not rocket science, It certainly can be testing to the Nth degree at times.
One of my pet hates is those who buy a set up, install a flippin great array straight out of the box and stick it where the neighbours/misses wont complain, then chuck a kilowatt into it regardless of whether they could maintain comms at a much lower power.
Here in the U.K we are blighted by certain ex communist countries operators who are using what was probably old military equipment running at god only knows what power levels shouting out their call signs obliterating the more interesting stations trying to be heard.
I was talking to a guy in Greenland last year, he was transmitting on 4 watts, I wound down the output of my FT950 to about the same level and we chatted for around 30mins until mr kilowatt came on shouting CQ CQ, never bothering to see if the frequency was in use, and assuming because he couldn't hear us we weren't there. I turned on my linear to full power and told him we were in conversation, with that, he just carried on. No manners!

 

Ah, yes, I take your point, If the experimentation was conducted with no real knowledge of the subject, any result that suddenly worked better by chance, would indeed be seen that way.
The context in which the ARRL and I were using it, was meant that despite applying the best available practice based on good understanding seemed not to perform as expected, then it is the non-electrical (although they still are in many ways) that need experimentation in the set up to site/reposition if possible or make changes that can by applying practical experience often lead to a more satisfactory outcome. Whilst not rocket science, It certainly can be testing to the Nth degree at times.

Yes, antenna siteing is electrical, very critically so. Many modern electrical/electronic courses tend to treat antennas like a transducer that converts circuit theory lump-sum, current, voltage parameters into radiowaves. A better way to think IMO is that antennas act more like matching transformers that transfers the constrained circuit electrical field energy that already surrounds the components and wiring into or from just another circuit that consists of the physical world electrical circuit. Understanding the properties of the physical world electrical circuit comes with experience that can be had by experiment or a deeper understanding of the electrical sciences.

 

Yes nsaspook is correct.

antennae technology is difficult you have to deal with;
type of antennae dipole , rot, wire or disk
thickness of the antennae rot/wire/dipole
length antennae in relation wavelength used 1/2 1/4 shorter using correction filters.
polarisation horizontal / vertical
height above ground does effect the impedance
temperature
air density
air moisture
termination / impedance
bandwidth system
obstacles
reflections at higher air layers

lots of parameters.
Some of them are uncontrolled and should be on the spot corrected. (using impedance matching circuits and virtual antennae length correction)

All above remarks become less critical when using an overkill on power on a short distance like mobile phone.( 2W @ 2.4 GHz in a few Km wide matrix of antennae)

Picbuster

 

Good electrical connection is very important, as well as the antenna placement.
One reason the Radio Australia transmitter site was situated in Shepparton was the land was flat so a good low takeoff for the radio signal was obtained.
One story I like to tell was about 40 years ago, one of my friends who will remain nameless, went down the padlock with his ham radio. He opened the feed just before the antenna and hooked his transceiver on. This was the European array if I remember correctly. Then he gave a CQ. Very good signals were received in Europ and when asked what his antenna was, he replied, "Just a commercial antenna".
The commercial antenna in question was a directional HF phased curtain array between towers of 210 feet high.
Not many hams get to use that sort of thing.

 

I liked the "Black Art" thing with RF. That meant that all throughout my career, most of my bosses were completely clueless as to how I did what I did - more than once did it get referred as "black art" or magic! Whenever one wanted a more detailed explanation, I would simply go to a white board and start writing down the field equations and start explaining what I was doing. It didn't take long for them to say, "okay, it looks like you have things under control..." and end the conversation.

Anyway, I thought every ham knew NOT to anodize aluminun antennas.

 

I liked the "Black Art" thing with RF. That meant that all throughout my career, most of my bosses were completely clueless as to how I did what I did - more than once did it get referred as "black art" or magic! Whenever one wanted a more detailed explanation, I would simply go to a white board and start writing down the field equations and start explaining what I was doing. It didn't take long for them to say, "okay, it looks like you have things under control..." and end the conversation.

Anyway, I thought every ham knew NOT to anodize aluminun antennas.

It's more geometry than art. Once you get the intuition of the phase changes (retarded Liénard-Wiechert potentials) in space from conductor surface(s) across space you can then easily see the transformation of electrical and magnetic properties across that space to another conductor or as propagating waves.

 

I liked the "Black Art" thing with RF. That meant that all throughout my career, most of my bosses were completely clueless as to how I did what I did - more than once did it get referred as "black art" or magic! Whenever one wanted a more detailed explanation, I would simply go to a white board and start writing down the field equations and start explaining what I was doing. It didn't take long for them to say, "okay, it looks like you have things under control..." and end the conversation.

Anyway, I thought every ham knew NOT to anodize aluminun antennas.

Yes I thought that too! But it must have slipped his mind when he was worried about the corrosion he had found. He's been a ham since the 50's and really did know better. At his age, I can understand his forgetfulness. I hope when I'm 94 I can still operate my radio.

 

Yes I thought that too! But it must have slipped his mind when he was worried about the corrosion he had found. He's been a ham since the 50's and really did know better. At his age, I can understand his forgetfulness. I hope when I'm 94 I can still operate my radio.

And a lot of other things!