Is This Normal? [For an antenna to be warm?]

[motofreak008]

Is it normal for a mobile antenna to heat up when a radio is transmitting? I think I am remembering right when it warns about portables having the ability to burn if the plastic has fallen off, is it true and does it apply to mobiles as well? Before you call me dumb or wonder what I am thinking, just remember I am still trying to learn a bunch of this stuff still and every time I ask, I always learn.

[please construct your subject lines correctly - which means please describe the EXACT issue or problem thanks! -Alex]

[FireCpt809]

It is possible for an antenna to get hot. Its not a good idea to be holding a mobile antenna when its transmitting. RF contact can burn. VHF 110w can leave a nice burn.

[Rayjk110]

I still have a small RF burn on my thumb from working on an XTS a few years ago. Hurts like hell for a second, and it'll leave a mark.

[motofreak008]

So pretty much, I shouldn't be too worried about it?

[kf4sqb]

"Is it normal" will depend on several factors. Exactly what type of antenna are you using, with what power level, in what frequency range. For example, a 1/4-wave vertical VHF with around 50 watts input shouldn't get warm. The same antenna with, say, 500 watts input, very well might. A base-loaded 1/2-wave, like the common AS-177, thats rated for (IIRC) 150 watts, with 140 watts or so input, the loading coil will very possibly get warm. A 1/4-wave low-band (think 102" CB whip) would probably take better than 5,000 watts for an extended period before it gets warm.

On the other hand, you may be referring to the fact that RF causes burns. This has nothing to do with the temperature of the antenna. This is caused by the fact that the RF "excites" the atoms in skin, making them move really fast, which generates heat. This is the same principle a microwave oven operates on. A microwave oven is really nothing but a large, high-powered radio transmitter, operating in the 2400-2800 MHz range IIRC. In this case, the frequency makes a lot of difference. The higher the frequency, the faster and deeper it will cause burns. Once you get to high enough frequencies, or high enough power levels, direct contact isn't even required for RF to burn you. A good rule of thumb is, if its transmitting, don't touch the antenna! RF burns are quite painful, trust me. I almost threw my old HT600 across the room one day, because I was stupid enough to key it up with no antenna attached, and my finger on the antenna port. Not deliberate, but the end result is the same.

[motofreak008]

Alright, it sounds like it was just a RF burn. It didn't leave a mark or anything, but it sure did hurt.