Radials? and the end fed 1/2 wave (EFHW)

[Marconi]

Looks just like the Imax.
Two coils (inner and outer) and all . . .

Yep Robb, but I think the Imax as fewer coils because it has less mismatch to overcome.

 

[W5LZ]

"O yeah, did y'all know the matching coil in the A99 was a single wire and the shield is probably tapped at the resonance point, with one end attached to the outside of the capacitor and the other end attached to the center conductor of the coax, and a the short tail, maybe 3" floating up inside the insulator inside the capacitor? If I could do the drawing like Nav did, I would draw it for you guys that are curious. That is the way it looks to me"

You just described a variable transformer which uses a fixed capacitor to form an impedance matching circuit. Which is exactly what the 'A99' and Imaxx uses.
The same thing can be done by using a fixed inductance and a variable capacitor. Why isn't it done that way? Probably because the variable capacitor for that circuit would be larger and a little more cumbersome to make into an antenna. Both would do the same thing, convert a high impedance to a lower impedance (or the other way around, a lower impedance to a higher impedance). I think that it was decided to do it this way because of the cost, and, because it's not quite as 'touchy' or 'picky' about finding an acceptable match. It's not as hard to do using the permeability of an inductor to do that adjusting and 'finding' as it would be with a variable capacitor and a fixed inductance. (The 'rings' act the same way as a 'slug' on the inside of a coil does.) It isn't the most efficient way of going about it, but it's certainly easier. Another aspect of doing it this way is that because a greater 'usable bandwidth' is always obtained at the expense of efficiency. The higher the efficiency the narrower the usable bandwidth of an antenna. (That applies to almost everything, not just antennas.)
- 'Doc

 

[Marconi]

"O yeah, did y'all know the matching coil in the A99 was a single wire and the shield is probably tapped at the resonance point, with one end attached to the outside of the capacitor and the other end attached to the center conductor of the coax, and a the short tail, maybe 3" floating up inside the insulator inside the capacitor? If I could do the drawing like Nav did, I would draw it for you guys that are curious. That is the way it looks to me"

You just described a variable transformer which uses a fixed capacitor to form an impedance matching circuit. Which is exactly what the 'A99' and Imaxx uses.
The same thing can be done by using a fixed inductance and a variable capacitor. Why isn't it done that way? Probably because the variable capacitor for that circuit would be larger and a little more cumbersome to make into an antenna. Both would do the same thing, convert a high impedance to a lower impedance (or the other way around, a lower impedance to a higher impedance). I think that it was decided to do it this way because of the cost, and, because it's not quite as 'touchy' or 'picky' about finding an acceptable match. It's not as hard to do using the permeability of an inductor to do that adjusting and 'finding' as it would be with a variable capacitor and a fixed inductance. (The 'rings' act the same way as a 'slug' on the inside of a coil does.) It isn't the most efficient way of going about it, but it's certainly easier. Another aspect of doing it this way is that because a greater 'usable bandwidth' is always obtained at the expense of efficiency. The higher the efficiency the narrower the usable bandwidth of an antenna. (That applies to almost everything, not just antennas.)
- 'Doc

I don't know circuits 'Doc, but it sounds about right to me.

Regarding your old adage regarding bandwidth and efficiency, I'll take your word for it. It's probably scientifically true, but can you tell it without using a $15,000 dollar testing machine the size of a large microwave.

I use to hear that all the time from my old mentor buddy, but after I was exposed to a working Sirio Gain Master, I began to think it was on the level of CBBS for me, and the magnitude of difference you suggest is nowhere near a humanly detectable range for guys just using a radio. I think we should be interested in effectiveness and leave the efficiency part to the engineers and scientist.

 

[nav2010]

Marconi wrote

I think we should be interested in effectiveness and leave the efficiency part to the engineers and scientist.

emmmmm

 

[bob85]

doc,
why don't you explain to your sheeple the mechanism by which a narrower bandwidth antenna is more efficient,

The higher the efficiency the narrower the usable bandwidth of an antenna. (That applies to almost everything, not just antennas.)
- 'Doc

smart folk say

"Note that bandwidth increased while efficiency increased. This happens in many cases.
Popular folklore tells us narrow antennas are efficient, but that is true only in a few specific cases. In most cases, bandwidth by itself tells us nothing about system efficiency!"


thanks.

 

[W5LZ]

Okay, just who would you recognize as an authority on antenna efficiency? Not 'system' efficiency, that's a completely different thingy.
The problem with that is that 'apples-n-oranges' thingy. We have to be talking about the same things or none of it will make sense. I think we can both agree about that, can't we? If not, then this whole thing is senseless.
- 'Doc

PS - I don't think I have any 'sheeple'? If by chance I do, I hope they don't plan on me feeding them. I can't care less if have some sort of 'following', I don't intend to have one, and I'd advise anyone not to follow me anywhere. If someone agrees with me/you, does that make them a 'sheeple'? If so, then there's a humongus number of them/us around.

 

[HomerBB]

I wish I had a sheeple. If I did I'd make it a very big one, change the h to a t, and it would be a steeple. Then I'd put it in my yard and put my antennas on it. And I wouldn't even have to feed it.

 

[BOOTY MONSTER]

some folks have minions :bdh:

 

[HomerBB]

some folks have minions :bdh:

kneel Booty, Homer is here :laugh:

 

[BOOTY MONSTER]

kneel Booty, Homer is here :laugh:

yesum massa Homer