Antenna Corrosion

I wouldn't think that oxidation would affect antenna reception much unless a significant amount of metal was gone. A thin layer of oxide is invisible to radio waves.

May be transmitting with large amount of broadcasting power, Rix. But, say receiving transmission in higher frequency bandwidths like FM and TV, has significant reception quality effect specially if you are located considerably far a part from the transmission tower.

I think for AM frequencies and other lower bandwidth than that, does not have a considerable effect.

Hmm,. I am just not quite sure. I am no electronics and communication guy.

Corrosion (not just simple oxidation) of transmitting elements can be problem, especially where the element is heavily pitted. Consider that at radio frequencies the bulk of the current travels within the surface of the element due to skin effect. The higher the frequency the thinner the 'skin' and the higher the current density at a given power. If the surface is heavily pitted you can get significant heating in the high-current parts of the element.

Exposed antenna elements are often anodised - a layer of oxide deliberately applied to protect the underlying metal. Antennas may also be enclosed by plastic or other dielectric housings far thicker than any oxide and this doesn't affect their performance significantly, so why do you think a comparably-thin layer of oxide would "degrade reception"? Consider the antennas in your cell phone or GPS receiver, for example, or those blade antennas you see on car roofs. Surrounded by/embedded in dielectrics. No, mate, simple oxidation has negligible effect on antenna performance.

I assume oxides behave like some sort of ceramic casing. In any case, dielectric will not interfere but, I think if it has to be ceramic-it will. I am not sure, but just installed a new antenna for my old man's analog tv. It took just a year that a significant deterioration of reception and the element were observed.

As most antenna elements are typically made of aluminium, the oxide would be aluminium oxide. In its form as alumina (Al₂O₃) - a ceramic - it is used through microwave frequencies because of its low loss.

Why do you think ceramics (generally) are not dielectrics?

Based on my experience, it's not common to see, they've used it on capacitors. But, thermal and electric insulators, yes, its common.

What of the ceramic RF 'windows' you see on magnetrons? To let the microwaves through whilst preserving the valve's internal vacuum?

The white rectangle in the centre of the waveguide flange. Alumina. Highly transparent to RF.

Oh, that's hard stuff , Andrew. Probably, a considerable depth on material science.

But, why is it if you are inside a basement or a concrete encapsulated building, its hard to find a GSM signal?

How is it possibly like that?

It's absorbed and/or blocked by surrounding materials, depending. Was does this have to do with oxide on antenna?

Yep, unbeknownst to many people, there is a 'lot' of water in concrete to absorb RF energy, never mind the rebar to act as a shield (freq. dependent) mesh/aperture size.

According the UK Concrete Society, moist concrete behaves as an electrolyte with resistivity of up to 100 Ω•m. Air-dried concrete has a resistivity in the order of 10 000 Ω•m, whilst oven-dry concrete has a resistivity in the order of 100 000 000 Ω•m.

Moist concrete would definitely attenuate RF; the higher the frequency the greater the attenuation. I think GSM uses 850, 900, 1800 and 1900 MHz, depending on location. The higher frequencies would definitely suffer.

It must be a material related EMW interference right? Other than, waves negating each other which can also be a consequent to material type and geometries.

Dielectrics are not ceramic? Sure on this?

Ceramics can be and frequently are a dielectric material. However many high-temperature superconductors are ceramic.

Quite agree that a doped ceramic is a super conductor under certain predetermined conditions, but to assume ceramics are not insulating is a misnomer. Otherwise many switching yards and sub stations and transmission lines would all be shorted to earth and the lad is not talking super conductors here. Aerials, (antenna) such as the one I assume he is referring to in the vodeo, are galvanised steel towers, solidly earthed, do have a naturally forming oxide coating on them, (white rust), which actually protects the steel work from corrosion. Just as on transmission line towers world wide.

Cleaning of all masts is left to the weather, as are insulators on lines, unless of course there is little rainfall to clean the dust and pollution off. Then cleaning is done by helicopter, pressurised water cleaning. (Clean water with no impurities in its make up).

https://www.youtube.com/watch?v=lcjhjna9jZE

But aerials in general don't need cleaning, particularly aluminium ones as, as soon as you obtain a bright clean surface on ali, it immediately oxides, so there is no sense in cleaning an ali or ali-alloy aerial.

http://www.evapco.eu/sites/evapco.eu/files/white_papers/36-White-Rust.pdf

This may help the lad in his findings.

Dielectrics can be plastic or glass or air, etc.

Did you mean to reply to #5 instead?

No Sir Andrew; 'Why do you think ceramics (generally) are not dielectrics' But on re-reading your statement you could have missed a comma and question mark out after 'Why', and asked a question. Or, meant to make a questionable statement.

Why, do you think.....? or

Why do you think....?

English! The language, or English, the people? In this case Me thinks English the language and punctuation.

Dry string is a great insulator and a good conductor when wet. And one of the best insulators for high voltage testing is... yes you got it.........water. Of course all impurities are removed, otherwise it conducts.

Out and over with the out and in.

"Why do you think ceramics (generally) are not dielectrics?" is exactly what I intended to ask, punctuation included.

How's about: "Why, gutmonarch, do you think ceramics (generally) are not dielectrics?"

Poor reception is possibly due to a bad connection on the aerial where the coax is connected or a movement from the original position. Maybe moved with a wind gust or a bird smacking into it.

The articles I found about antenna corrosion were mostly concerned with corrosion at connection joints. This makes better sense to me for it being an easier failure point for many reasons; moisture wicking, impedance reflections, dissimilar metal corrosion. The next more frequent antenna corrosion concern was structural support for obvious reasons. I suppose there are a few frequencies and scenarios where skin effect resistance changes might make a difference but...

The most common technique I know of to minimize oxidation concerns of antenna elements is to apply a thin sapphire coating to the antenna elements.

How do you know that, "Oxides on an antenna usually degrade reception"?

Are you sure about this?

How do you know?

Why do you ask? Bored?

How often do you search for an answer before asking these inane questions?

Lyn:

Speaking of questions. I have one. ( Gutmonarch do you mind ? )

Lyn: do you happen to know the torque specs for the upper intake manifold bolts for a 1999 Ford explorer with a 5.0 V - 8 SEFI Engine.

Here is a picture of the upper intake manifold. As you can see, there are thread taps for 6 bolts. One more picture

When I am in a trance . I mean confused.

There must be a way, to counter that effect, I am thinking. Probably, just the connection corrosion.

I wonder what AH would say 'bout this. I never read his posts these days.

As others have noted different manufacturers apply surface finishes, but for seaborne and coastal installations copper antenna's are the norm, joints still need protection and often the whole thing is painted with a sealing lacquer.

Thanks, John.