Mounting a Ball Mount

[AB9DF]

I am installing a ball mount on a 97 Astro Van.  I am installing a Hustler ball mount with a spring and a post of 54 inches.  However, I would need to install the ball mount pretty low on the left rear panel in order to not have it so high above the vehicle.  My main concern is to keep the resonator above the roof line of the van.  My question is related to installing a shorter rod and putting the ball mount higher up.  This is due to accessibility issues on the van.  Does the ball mount itself need to be low?  Is there any problem fundamentally if I use a shorter post as long as the resonator is higher than the roof line?

Any insight would be helpful
Rob AB9DF  

[W5FYI]

The rule-of-thumb is "higher is better." Ideally, from an efficiency standpoint, the mount should be on the van's roof. But I can understand your (or your XYL's) desire to keep the profile low.

Before you decide where to place the mount, consider that most of the antenna's radiation will be from the section below the resonator, and not so much from the loading coil or whip. The longer and higher you can get the base rod, and the further away from the car's metal body, the better. But by all means, keep the resonator away from swaying near body, to minimize inductance changes while driving.

I don't know about your van's skin, but cars with fiberglass and plastic bodies affect the antenna less, so low mounting is not so much of a problem.

Stew, W5FYI

[WA3SKN]

The Hustler design used 54 inches so it could be used on 6 meters, also.  Their resonators are designed around this.
73s

-Mike.

[AA4PB]

Hustler also makes a 22-inch mast but they supply longer whips for the loading coil when you use the short mast.

[W3LK]

Another consideration is the thickness of the metal in the sidewall panel. A large backing plate will likely be necessary to keep the sidewall from flexing.

I suggest you take a look at www.k0bg.com. Alan has a whole section on such installations.

73,

Lon - W3LK
Naugatuck, Connecticut

[K0BG]

There are a few things to be aware of besides strengthening the back side of the mount.

The Hustler ballmount is flimsy at best. The two halves are stamped stainless steel, and the rolled ferrule which holds the sides apart when you tighten the cross bolt is not welded. So, if you tighten it too much, the ferrule splits apart, which loosens the ball, and the antenna falls over. It is just barely adequate for the smaller coils.

The fold over mast's hinge isn't very sturdy, and after a while the hinge loosens and causes an intermittent connection. This is why you see so many of them with a copper strap across the hinge.

Which ever mast you use, don't over tighten the coil. It is held on by just 5 threads which is bad enough. But, when you over tighten them, the pressed in threaded post loosens, with predictable results.

In spite of their problems (until just recently), it's been the most popular HF mobile antenna. High Sierra now has that honor.

Alan, KØBG
www.k0bg.com

[AB9DF]

I guess I am sort of nervous of drilling the hole but nonetheless I am going to do it.  Just to be clear, My Astro van has a place on the left rear panel about the level of the top of the tire where I could install it.  If I use the 54 inch rod the resonator would be about 12 inches about the roof line.  I believe however I might be able to mount the ball mount in the same area but about 12 inches from the top.  Then use a spring and then a 22" rod and now I would have my resonator about 18 inches above the roof line and not have so much rod parallel to the vehicle.  Meaning that I dont have 4 ft but rather 1 foot of rod along side my van.  From an efficiency point of view, it seems that the higher ball mount and shorter rod would be better.  What do you think?  Sorry for all the questions but I have never done this before.  
Thanks!
Rob AB9DF