Question for the antenna gurus

[Watergate]

I know all installations are different depending on individual circumstances. So here are my circumstances.

My mobile antenna can only be mounted on a mirror. I can't drill new holes in the truck. I can mount an antenna 80 inches tall. No higher. It takes 28 inches to clear the roof line from the mounting point.

So keeping that in mind, I ran a Hustler Mobile HF with the 10 meter "super resonator." That got me clear of the roof line with the coil and as tall as I could get on the truck. It was also broadbanded enough to cover all of 10 and 90% of 11 meters.

However the mast was too flimsy. The mast was thin wall aluminum tubing 54" tall.

My question is, if I were to make a new mast out of something stronger, like steel pipe, how would that affect the resonance of the antenna.

I have a mounting solution to hold that heavy of an antenna, even in strong winds at 70 mph, I just don't know what effect it will have on the antennas resonance.

Would 54" of 9/16 inch steel pipe look the same as 54" of 1/2 inch aluminum tubing to RF?

 

[W5LZ]

As long as that mast is the same length as the 'flimsy' one, and is metal or at least an electrical conductor, it ought'a work okay. You might have to re-tune the antenna slightly, but that'd be the case no matter what you used to replace the existing mast.
- 'Doc

(I ain't no 'guru', forget that. I just have played with antennas for a while.)

 

[wavrider]

As DOC posted.

RF is looking for electrical length of whatever is being used as an antenna.

I have made many antennas out of EMT conduit and they work well, material is not expensive and easy to find at the big box stores.

102" steel whip is just that, steel .

 

[Captain Kilowatt]

I would be concerned about rust on a steel mobile antenna. If you could use some stainless steel that would be great. You could try 1/2 or even 3/4 inch copper pipe too. That may work out well. Try and use type L or even type K if you can find it as it is thicker walled and more rigid.

 

[Watergate]

Thanks all. I was not sure if going from thin wall 1/2 inch aluminum to thick wall 9/16 inch steel would affect it too much.

Captain, I am still working out the rust issue in my head. Paint probably, but it would have to be RF neutral.

I need to head to the plumbing store and check out some copper as well. I had thought about that. I just have everything else sitting around to do it with steel.

 

[Beetle]

Not sure what "RF neutral" means. If the paint has a metallic or otherwise conductive quality, just be sure not to paint those parts that are supposed to be insulators or at least supposed to be isolated from other parts.

 

[Watergate]

Not sure what "RF neutral" means. If the paint has a metallic or otherwise conductive quality, just be sure not to paint those parts that are supposed to be insulators or at least supposed to be isolated from other parts.

Just easier to use non-metallic paint than to think of the words non-metallic to put in a post for some reason tonight.

RF neutral as in zero interaction with RF waves. In other words, non conductive. I don't want Krylon interfering with a QSO.

 

[hookedon6]

... I ran a Hustler Mobile HF with the 10 meter "super resonator." That got me clear of the roof line with the coil and as tall as I could get on the truck. It was also broadbanded enough to cover all of 10 and 90% of 11 meters.

However the mast was too flimsy. The mast was thin wall aluminum tubing 54" tall...

have you considered a "screwdriver" antenna? go here http://www.qrz.com/db/N0AZZ and look @ the hitch mount

 

[Watergate]

have you considered a "screwdriver" antenna? go here http://www.qrz.com/db/N0AZZ and look @ the hitch mount

Screwdriver is in the works. Right now I'm putting money aside for a full HF radio and screwdriver. That's why I haven't considered a solid aluminum rod for this. The cost of it takes away from my Hi-Q.

 

[HomerBB]

Another option is to replace the aluminum shaft with a thicker walled aluminum tube. It will be sturdier, not subject to rust, and the additional thickness will be toward the center of the tube instead of adding to the current diameter. In other words, a thicker walled 1/2" OD aluminum tube.

 

[Beetle]

Just easier to use non-metallic paint than to think of the words non-metallic to put in a post for some reason tonight.

RF neutral as in zero interaction with RF waves. In other words, non conductive. I don't want Krylon interfering with a QSO.

So you want to put paint on a metallic surface that's radiating RF. Basically, you're putting a layer of metal on top of a surface that's metal. Won't hurt a thing unless you paint pieces that are meant to be insulators. Krylon won't interfere with anything. It might fractionally change the Vf of the radiator, but I doubt you'd see any change at all without some expensive instruments.

 

[W5LZ]

Very basically you want to add a layer of a conductive material to the surface of a conductive material. Unless there's a humongus difference in diameter, or conductivity, that additional layer shouldn't make any differences at all (or at least differences that are measurable). The only 'trick' is to NOT put a conductive layer of stuff on things that shouldn't do any conducting.
Nothing 'new' in that, just a different way of saying/looking at it.
- 'Doc

 

[Watergate]

So you want to put paint on a metallic surface that's radiating RF. Basically, you're putting a layer of metal on top of a surface that's metal. Won't hurt a thing unless you paint pieces that are meant to be insulators. Krylon won't interfere with anything. It might fractionally change the Vf of the radiator, but I doubt you'd see any change at all without some expensive instruments.

Actually Beetle, I may have just found some bad info on the net (I know, hard to believe right?), but I did read somewhere, a while back, that some paints can effectively trap the RF by blocking it and not allowing it to leave the surface of the metal. I've been searching for that site I read that on and can't find it.

I trust what I read on this site however. You guys have a huge amount of real world experience, so I'll not worry about paint.

Thanks again all of you "iElmers"

Might still go the copper route if I can do it cheap enough.

 

[wavrider]

If you do find that site the military would be interested in that paint probably. They have spent billions on stealth and all they had to do was paint the aircraft with rf absorbing paint?

Actually Beetle, I may have just found some bad info on the net (I know, hard to believe right?), but I did read somewhere, a while back, that some paints can effectively trap the RF by blocking it and not allowing it to leave the surface of the metal. I've been searching for that site I read that on and can't find it.

I trust what I read on this site however. You guys have a huge amount of real world experience, so I'll not worry about paint.

Thanks again all of you "iElmers"

Might still go the copper route if I can do it cheap enough.

 

[Watergate]

If you do find that site the military would be interested in that paint probably. They have spent billions on stealth and all they had to do was paint the aircraft with rf absorbing paint?

It had more to do with avoiding certain carbon elements in the paint.

The stealth planes do utilize special paint. But they are designed to absorb rf not block it. Blocking it would create a radar image.

The Blackbird is painted with a black paint that consists of a pigmentation containing minute iron balls. These dissipate electro-magnetically-generated energy and effectively lower the chances of the plane being picked up by radar.

There's this stuff too.
http://www.amazon.com/gp/aw/d/B0025Z8GAY

But I think from reading about it, it's just a conductive paint and would radiate a signal.