Radio Program / Podcast Friday

I am on a well-known broadcast/podcast, I think Friday. If you are concerned that I haven’t given someone credit or that history has been misrepresented: I was recorded for three hours, and what they called me to fact-check would be just a few minutes on the air. The producer was really nice and did his absolute best, and I probably did say what you wanted, and because of time constraints of a 15-30 minute program where I was only one of several guests, very little made it on the air. History was also simplified by the program to make it comprehensible to the audience, for example USENET became a bulletin board and postings became tweets.

I do my best for the community with the press that I frequently have to deal with. Much of the community rarely deal with the press and aren’t aware of the issues, the main one being that I can only very rarely get them to say all that I want, the way I said it, and that my words generally pass through a reporter, an editor, a proofreader, and maybe other people before you read them.

Radio Antennas and Anti-Seize Compound

Amateur Radio operators like to put antennas outside and in the air. Once there, we might not be able to reach them for a long time. But someday they will need to be serviced or disassembled.

Not everyone learns right away: you should use anti-seize compound when assembling your antenna. It should go on every mating of two fasteners, and every place where a tube slides into another tube. Anti-seize compound is a special lubricant, sometimes mixed with microscopic copper, zinc, aluminum, or nickel powder, which keeps metal fasteners from getting stuck. I once disassembled an antenna that had been left in the air for 15 years, at a site a couple of miles from the ocean and its salt spray. Because the assembler had diligently used anti-seize compound, the entire thing came apart easily, and all of the fasteners, probably stainless steel, could be reused.

You should be using stainless steel fasteners for things that live outside, as these will best survive an extended time outdoors without becoming a lump of rust. But stainless steel has special needs: The friction of two threaded stainless steel fasteners mating causes galling, microscopic debris that can lock two fasteners together, or they can cold-weld, which causes the two surfaces to fuse together. So, stainless steel fasteners always need anti-seize compound to preserve their ability to be disassembled.

Similarly, you should use anti-seize when you mate antenna parts like nesting tubes together. Or don’t expect them to come apart again in a decade.

Some people are concerned about the conductivity of the anti-seize compound, even going to the trouble of measuring its DC conductivity with an ohmmeter. This is a little naivé, because antennas carry RF, not DC. The metal-filled kind of anti-seize compound is more conductive, obviously, but in general you don’t need to be concerned about its conductivity. The metal parts of the antenna will generally DC-couple even in the presence of a non-conductive lubricant, the contact surfaces just push it aside and the lubricant fills gaps. And even if they didn’t, the capacitive coupling between the metal parts would be sufficient. Metal parts are in general not bare metal: both stainless steel and aluminum resist rust because of a protective oxide coating that they form immediately when they contact air. But these parts maintain DC electrical contact even though their oxides are insulators. They rub it off, or it’s too thin to matter.

What is the best anti-seize compound to use for antennas? Most anti-seize compound is designed for other applications, in particular use in automotive engines. So, you’ll see it rated for use with temperatures in the thousands of degrees Farenheit. Obviously we don’t need this for our antennas that probably won’t exceed 150° F.

However, our antennas are outdoors in a harsh environment. Acid rain is everywhere, and birds drop guano on antennas that becomes phosphoric and nitric acid through bacterial processes (for the bio heads: denitrification, glycolysis, probably others). When you have two different metals touching each other, and acid, you have all of the parts of a battery: a cathode, an anode, and electrolyte; and the result is galvanic corrosion, a form of electrically and chemically accelerated rusting. Even mildly impure water is sufficient to be the electrolyte, so the potential for galvanic corrosion is everywhere that dissimilar metals touch.

It’s a characteristic of the electro-chemical reaction of a battery that the anodes donate electrons to the circuit and the cathodes receive them. Anodes corrode as they lose electrons, and the cathodes may get coated with some chemical by-product, but generally cathodes don’t corrode. In our antennas combination of two metals, one will be the cathode and one the anode. Which is which? You figure that out with the galvanic series, a table of which metals are better, or worse, electron donors. But why would you need to know?

A very common strategy for defeating galvanic corrosion is the use of a sacrificial anode. For example, most boats and water heaters contain one, and you’ll sometimes come upon a marked cover for one in the street, as they’re used to protect most underground infrastructure. The sacricifical anode is generally zinc or magnesium, as those are on the bottom of the galvanic series. That means that other metal connected to the sacrificial anode will be a cathode and won’t be subject to galvanic corrosion, while the sacrificial anode will be, sacrificing itself for the good of the cathode!

So, this brings us back to the anti-seize compound. As I mentioned, these are available with zinc filling, aluminum, copper, or nickel. Our antennas are generally aluminum. Copper and nickel are both above aluminum on the galvanic series, and thus in combination with them, our aluminum antenna part would be the anode, and would be subject to galvanic corrosion in combination with copper or nickel anti-seize. This might be micoscopic, but the result is going to be rougher surfaces when we try to disassemble two nesting tubes. What if we use zinc-filled anti-seize? Zinc is below aluminum on the galvanic series, and thus the zinc would be the anode, and maybe some of the zinc in the anti-seize will sacrifice itself to keep our aluminum antenna parts pristine as acids intrude into the connection. So, I’m going to use zinc anti-seize on my antenna, even though a lot of hams swear by Jet-Lube SS-30, a fine brand of copper anti-seize sold by, among others, DX Engineering.

An alternative is the aluminum-filled anti-seize sold by InnovAntennas. In the joining of two aluminum elements there would be no dissimilar metal issues. However, entertainingly their own catalog page shows the elements secured with a stainless steel pipe clamp, making it clear to me that there would still be dissimilar metals issues. I’m going to stick with zinc where the pipe clamp would be, and with any dissimilar metal contact, but maybe this aluminum paste is a good idea for between the elements. Permatex also makes an “Aluminum” anti-seize, but they describe it as a blend of aluminum, copper, and graphite, so I assume it’s called “Aluminum” because it’s intended for aluminum engine blocks.

When would copper anti-seize be appropriate? Well, I think it’s made for car engines, where heat is a problem and the main material used is steel. Jet-lube might have been designed for aviation, back before aluminum was in as much use. Steel and iron are above copper on the galvanic series and thus copper could be a sacrificial anode. Engines often have a large sacrificial anode, or more than one, somewhere within both their oil and cooling circuits, and this will often be zinc or magnesium.

Copper anti-seize is also appropriate for stainless steel antenna parts, at least the ones that don’t touch aluminum. Zinc would work at least as well, including for parts that touch aluminum.

There are places that anti-seize doesn’t belong: don’t put it on moving parts, and don’t bridge things that are supposed to be insulators with it. That means definitely don’t put it on your coaxial connectors! Don’t put it where it might collect lots of dust, it’s meant for where metal is permanently mated with other metal, and won’t help elsewhere.