Center load VS. Base Load?

[unit_399]

The important thing to remember about loaded antennas, is that the signal radiates from THE TOP OF THE COIL. This is an important consideration when looking at antennas for mobile use. So it would follow that (for mobile use) top -loaded would be the best, followed by center-load and bottom-load. Wire-wound antennas, like the Firestick are actually top-loaded since the lower portion of the winding is too widely spaced to act an an inductor. Only the top portion of the wind acts as a loading coil. All loaded antennas have some inductive losses, and this can also be a consideration. Whips radiate from the top, which gives the maximum signal height in mobile use. However, loaded antennas with BIG coils have greater bandwidth. So there is always a trade off.

- 399

 

[hotrod]

probably a better understanding about why fiber-glass antenna is worse can be had by reading the k0bg page on antenna efficiency.
(An antenna with high Q is very efficient, but has more narrow operating bandwidth. cant have both.)
The more material within the field of the coil, the more the Q will be reduced.
Wilson 5000 and predator 10k are good antennas because their coil has high Q.
Fiberglass has poor Q coil because there is so much material around it and the wire size is too small, and it has alot of distributed capacitance. Coil Q is more important than base-load vs center-load.

Like booty said, the ground plane is half the antenna. The best antenna will be garbage if you have ground losses.

so lets see if i got it rite an antenna that has less
bandwidth is more efficient.now anther question years ago i did test a wilson silverload 4ft?
against a wilson 5000 mag mount and the silver load did surprisingly just about as good
as the 5k .now is this because its more narrow banded or just cause its top loaded

 

[W5LZ]

hotrod,
While those things contribute to the whole thing, they are not the 'end-all' that 'cures' things. Don't get too 'tied-up' in just a single aspect, you have to consider all of it.
Yes, a narrower 'bandwidth' does usually contribute to a higher efficiency. But it depends on just how efficient that antenna was to start with, 'where' it could put a signal. Antennas of comparable sizes/length have comparable radiation patterns. That does not mean that one particular antenna is all that much 'better' than another. It really depends on too many other things. One of those 'relative' thingys.
Coils.
Sure, you typically want the most efficient, highest 'Q' that's -practical-. The size of the wire making up that coil sort of determines it's power handling ability, not it's 'Q'. 'Short' and 'fat' coils are typically more efficient than 'tall' and 'skinny' coils. But if that 'short/fat' coil is in an antenna that isn't all that efficient to start with, it won't 'help' things all that much. Some, sure! But it's the total efficiency that counts most.
Beauty is in the eye of the beholder! 'Looks' has very little to do with efficiency unless you are talking only about 'looks'. At HF, it it ain't big and ugly, it probably isn't very efficient. That's just HF.
- 'Doc

(And of course, my antenna is prettier than yours!)

 

[BOOTY MONSTER]

The important thing to remember about loaded antennas, is that the signal radiates from THE TOP OF THE COIL. This is an important consideration when looking at antennas for mobile use. So it would follow that (for mobile use) top -loaded would be the best, followed by center-load and bottom-load. Wire-wound antennas, like the Firestick are actually top-loaded since the lower portion of the winding is too widely spaced to act an an inductor. Only the top portion of the wind acts as a loading coil. All loaded antennas have some inductive losses, and this can also be a consideration. Whips radiate from the top, which gives the maximum signal height in mobile use. However, loaded antennas with BIG coils have greater bandwidth. So there is always a trade off.

- 399

most top loaded antennas just have a few to several inches of stinger or radiator above the coil . it doesnt make sense to me that a few inches at the top would be more effective than several feet of stinger or radiator above a center loaded or base loaded antenna .

did i miss understand something ? can you explain it in more detail ?

 

[W5LZ]

There are more than one misconception in the last few posts. Not being able to explain this very well, I'd advise you to find someone who can. I can think of two off hand, K0BG and K5BUG. Ask either and I'll bet you they can tell you what you want to know. 'BUG' is harder to get a hold of than 'BG'.
- 'Doc

 

[rabbiporkchop]

top vs center vs bottom

Top is best. Center is not as good. Bottom is worst, but ok for the roof of a car.