how does vhf coil work

[Se7en]

i am curious how a coil antenna works.
im talking about monoband VHF & monoband UHF.
including dual band vhf uhf antennas.

today i broke my ANLI dual bander and what was inside? capacitors&copper wire wrapped around plastic insulater, they didnt break but the wire soldered in line with them to the top metal coil antenna which i fixed no problem ( better then they made it )!

the upper whip is 4 turns. while inside below it in a plastic sleeve is several turns of copper wire.

but im curious if lets say you have a 2m 5/8 antenna.... the whip is 52" or more.... now some antennas have the same whip but the center of the middle is like a curly fry OR Internal coil.... what if you took the whip and made all of it coils? or did it every 2" to make the whip less long, and still be strong?

same i fashion for any vhf uhf shf ehf THz.

 

[W5LZ]

Did you by chance notice ow that coil was wound? How it's wound on that form can make a huge difference. And did you notice if that coil and capacitor were in parallel or in series? (I'd ask if that capacitor had a value printed on it, but I really doubt if it did.)
For a multi-band antenna as you described there are a couple of ways of going about adding 'elements' to make an array for the higher frequency band. That coil/coil and capacitor make up a tuned circuit that is invisible to a lower frequency, but is a 'timing'/phasing device at the higher frequency. The length of the 'whip' between those coils also plays a part in that 'timing'/phasing. At the higher frequency each 'element' acts as a separate antenna stacked on top of another one, and changes the shape of the radiation pattern, where the signal goes, which is typically squashed to a lower angle and made 'stronger'.
The lower frequency doesn't 'see' those coils/capacitors, but thinks it's just a straight length of antenna. Unless one of those coils is to break that whip into two (or more) elements on the lower frequency (band).
That's not an exact or scientific explanation, but it does describe what happens with a vertical array antenna.
Confused yet??
- 'Doc

 

[Se7en]

Did you by chance notice ow that coil was wound? How it's wound on that form can make a huge difference. And did you notice if that coil and capacitor were in parallel or in series? (I'd ask if that capacitor had a value printed on it, but I really doubt if it did.)
For a multi-band antenna as you described there are a couple of ways of going about adding 'elements' to make an array for the higher frequency band. That coil/coil and capacitor make up a tuned circuit that is invisible to a lower frequency, but is a 'timing'/phasing device at the higher frequency. The length of the 'whip' between those coils also plays a part in that 'timing'/phasing. At the higher frequency each 'element' acts as a separate antenna stacked on top of another one, and changes the shape of the radiation pattern, where the signal goes, which is typically squashed to a lower angle and made 'stronger'.
The lower frequency doesn't 'see' those coils/capacitors, but thinks it's just a straight length of antenna. Unless one of those coils is to break that whip into two (or more) elements on the lower frequency (band).
That's not an exact or scientific explanation, but it does describe what happens with a vertical array antenna.
Confused yet??
- 'Doc

no not confused it makes sense to a point. It has two coils stacked one is inside and the other is outside on top. the capacitors are in series. when using a VOM it is ODD that GROUND is connected to the top of the external coil. while checking with a VOM on the inner pin HOT inside the nmo it stops at a capacitor.

 

[Beetle]

DC from the VOM stops at the capacitor. RF passes right through.

 

[W5LZ]

You lost me on that last description, I'm not sure I understand what you are talking about, how the thing is made. I'm not familiar with that particular antenna, so I guess that's not unusual for me to be confused. Sorry.
- 'Doc

 

[Se7en]

You lost me on that last description, I'm not sure I understand what you are talking about, how the thing is made. I'm not familiar with that particular antenna, so I guess that's not unusual for me to be confused. Sorry.
- 'Doc

okay, is there a way to remove the lower "whip" and be replaced by a spring?

i think i should purchase MFJ antenna analyzer

 

[W5LZ]

That lower wgip is part of the design for that antenna. So, if you replace it with something you have to make sure the finished height (of that lower whip) is still the same. If you want to replace part of that lower whip with a spring then make very sure that when it's all assembled that the height of the spring and remaining portion of that lower whip is the same length as the original lower whip. Otherwise, the antenna won't be resonant in the same spots, or probably even close.
I suppose it can be done, but I don't think I've ever seen it done.
- 'Doc