WWII Antenna "Shape"

[Another Ahab]

Huh!?

There can be a number of different reasons for curves and loops. Sometimes it's tuning, more often it's for shaping the radiation pattern.

Here's one that will torque your brain - picture a whip antenna with a spiral connected to the base of the radiator on one end and to the ground plane on its other end. A dead short.

What's it for? Well, it's not a dead short at radio frequencies - it's actually a high impedance. At DC, it's a short, of course, but that allows static to bleed off, which is why it's there.

 

[MarcusOReallyus]

Yep, that's what I said! AC works quite differently from DC. At resonant frequencies, it gets downright weird. That's what makes telecommunications possible.

This can make it very difficult to get rid of unwanted induced voltages - what is a low impedance at one frequency may be a high impedance at another, so you try to ground out the unwanted signal and it just laughs at you.

 

[Another Ahab]

Yep, that's what I said! AC works quite differently from DC. At resonant frequencies, it gets downright weird. That's what makes telecommunications possible.

This can make it very difficult to get rid of unwanted induced voltages - what is a low impedance at one frequency may be a high impedance at another, so you try to ground out the unwanted signal and it just laughs at you.

Want to know more; confess to knowing little:

- Guessing that DC produces a signal with less noise

I can kind of see that, but is that simplification on my part valid at all in the world of R.A.D.I.O.?

 

[MarcusOReallyus]

Well, DC itself doesn't carry a signal. We can impose a signal (information) on it, but that signal itself isn't DC.

Wrapping your head around resonant circuits takes a bit more learning that can be passed on in a forum like this. It's fun stuff.