Predator Competition "Bad to the Bone"

[AudioShockwav]

2. Use coils that are short and wide rather than long and skinny
3. Don't put a cap hat directly on top of a coil - some separation is necessary

If you take that same antenna, and remove the long thin coil, put a coil in that is wider and shorter, 2 inches around, and 2 inches long, them move the same 24 inch Cap hat above the coil 24 inches, the Current above the coil goes from 73% to 94%.
W8JI has done extensive testing with loaded antennas using custom made test equipment and the resulting testing has proved this.
It is ironic that the antenna that mole pictured, is a perfect example of just about the worst antenna you could build compared to his testing.
The only antenna that showed more current loss was one with a long 12 inch by 3 inch coil, with a 24 inch cap hat 24 inches above the coil...... that antenna showed a 27% loss in current above the coil as compared to the current below the coil.
The size and length of the coil, the size of the Cap hat and where it is placed all play critical role`s in loaded mobile antennas.

73
jeff

 

[15minigrass]

Does the cap hat make up for the rest of the whip which are included in every mobile coiled antenna or is that a top loaded coil? Looks heavy. But effiency is what were looking @ here right?

Nice build, 1-5...

If you need to shorten a mobile antenna for whatever reason, the antenna will have greater efficiency if you can use a capacity hat and decrease the amount of coil. The larger the hat, the better, but it becomes unmanageable at some point when it becomes too large. You can add more capacitance by using more hat elements. Here are a few ideas that are in the marketplace:

Here are some simple, proven rules you can use to help designing more efficient short, loaded antenna:

1. Use Cap hats
2. Use coils that are short and wide rather than long and skinny
3. Don't put a cap hat directly on top of a coil - some separation is necessary
4. Don't mix and match coil sizes on the same antenna if you can help it. Doing so may be necessary if you're building multiband antennas (think traps, etc.), but there's no reason to do it on a single band antenna.
5. Don't make up your own descriptions for how it works when you're done. It's OK if you don't fully understand what you created (happens to me all the time), but don't make shit up.

 

[AudioShockwav]

Good Morning James,
Grab a cup of coffee, and have a look at this page by W8JI
Start at the top, and read down.
I have been studying this info for a while now and it is still hard to get my head wrapped around all of it, I have had to read, and go away for a while and come back and re-read.
But as you read and think about it, and then think about things that you have done with your own antennas, it will start to make sense.
It is worth the time if you like to play with antennas.Mobile antennas, short verticals, loading coil loss,and loading coil current


here is a quote from the page that might peak your interest.
Written By W8JI:

Common myths about inductor behavior:

One common myth is loading coil current is reduced by standing waves or by the fraction of "electrical degrees" the inductor "replaces" as it passes through the length of wire in the coil. There are two reasons cited for this. One idea is the current is reduced because the loading coil replaces a certain amount of "electrical degrees" of antenna area, substituting or replacing the normal current taper seen in an unterminated antenna. The other idea is that series loss resistances cause a current reduction.

We often find inexperienced builders of 5/8th wl antennas think the "loading coil" needs to contain 1/8th wavelength of wire in order to make the 5/8th wave antenna a "3/4wl resonant antenna". They think, through wire length alone, the wire creates a low feed impedance by making the antenna three-quarters of a wave long electrically. In other cases claims are made one half-wave of wire wound on a compact form causes a 180-degree current delay, making a compact coil useful for phasing in a collinear array.

The basic flaw is the above ideas do not account for what actually occurs in a coil. The flawed viewpoint is current goes in one end, winds its way around through the physical length of wire in the coil, and after a time delay caused by the copper path length current appears at the other end. There is a physical mechanism that prevents what we might intuitively think happens from actually happening. A coil or loading inductor has magnetic mutual coupling between turns. The physical mechanism is the magnetic field in the coil!

You have to stop thinking about a loading coil as a coil of wire that the current goes into the bottom of the metal in the coil, and winds round and round until it exits the top, like water flowing through a tube.
The current creates a magnetic field as it flows through the coil, this makes things much more complacated that just the water through the tube view of what is happening.


73
Jeff