Antenna on Trailer

[LT-EMTC9]

My Dept is putting together and incident support trailer that will carry extra supplies and act as a secondary communications set up. My Chief has asked me to install a GM300 VHF in it. The trailer roof is made out of aluminum, any idea on the best way to mount the antenna? I have never dealt with aluminum before, obviously the antenna will not ground properly to it correct? Thanks.

[tvsjr]

You are aware that most vehicles these days are aluminum?

Aluminum conducts just fine... install a typical mobile mount in the roof and you're good to go.

[kf4sqb]

Just make sure you use plenty of de-ox compound on everything that contacts the aluminum.

[LT-EMTC9]

Ha-Ha, glad I posted this, I was always under the impression that aluminum would not conduct. And now that you guys have replied you have made me realize the roof on our ambulance is aluminum. My mistake, as always thanks for the help!

[kf4sqb]

Aluminum is, indeed, an excellent conductor. In fact, a lot of residential electrical services have aluminum wire from the power company's meter to the inside panelbox. Furthermore, the vast majority of the power company's overhead high-voltage lines are also aluminum (with a steel "messenger" cable in the middle of the bundle to support it).

[firefighter13669]

on are special response trailor we used what is called a fender mount and mounted it at the top of the front side of the trailor

[oh6hz]

Aluminum is, indeed, an excellent conductor.

Yes, even many (most?) antennas are made of aluminium. Just look at some normal TV-antennas. I don't think you even need any de-ox compound. Aluminium corrodes immediately when you cut it but the oxidised aluminium won't fall off like rust does - it actually forms a nice protective layer.

[kf4sqb]

I don't think you even need any de-ox compound.

You are correct, but what about when it corrodes between two parts that need to be electrically connected? Corrosion is, basically, "crystallized" aluminum. What happens when you run current through a crystal? To put it simply, the oldest form of "diode" is made from a base metal, sandwiched together with that metal's oxide, in other words a corroded form of the metal. So, your corroded connection between aluminum parts is now a rectifier, and can and will generate extremely broadband RF noise, which will cause extreme degradation of receiver performance, and horrible spurious emissions when you transmit. Any aluminum part of any antenna system should be de-ox'ed when assembled, especially when the aluminum contacts any dissimilar metal. In summary, corrosion on parts exposed to the elements: good. Corrosion on parts that touch and need an good electrical connection: BAD, BAD, BAD!!!

[oh6hz]

You are correct, but what about when it corrodes between two parts that need to be electrically connected?

My point was that aluminium is already corroded when you apply the de-ox compound as corrosion happens immediately when the metal meets air.

It's true that in some circumstances you might get a lot of corrosion. It probably depends a bit on the climate. I have seen some very heavy duty antennas in quite bad shape on a coal fired power plant, probably because of acids or other pollution from the chimney. I agree that corrosion of that magnitude might cause problems and protecting the metal will keep you free from them for quite a while.

[kf4sqb]

My point was that aluminium is already corroded when you apply the de-ox compound as corrosion happens immediately when the metal meets air.

OK, good point. I guess I should've pointed out that the metal need to be cleaned very well before the de-ox is applied. A good, clean wire brush will usually suffice to clean the surface, unless it is very dirty or heavily corroded.

[Jatla]

Galvanic corrosion occurs with dissimilar metals. Aluminum is very high on the list compared to Brass (most NMO mounts are made of Brass), and will be corroded far more than most metals intimately attached to it. {The higher the difference between the two metals in galvanic potential, the worse the corrosion will be.} With any moisture present to facilitate it, a crude battery is created and the aluminum is more rapidly converted to an oxide than a metal lower on the galvanic potential list. Thats why what are known as "sacrificial anodes" are made of Aluminum or Magnesium and bolted to steel structures for protection. So please make sure any O-Rings are in good order and properly lubricated prior to installation in the grooves of the mounts.

See below link...

http://www.engineersedge.com/galvanic_capatability.htm

Good Luck. Just do a quality install with attention to detail, and all should be well.