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Antennas for dummies

prkaye

Well Known Member
I think I need a better understanding of how antennas work. Looking at my new Archer (clone) Nav antenna, i notice that almost the entire thing is grounded. There is only a 2.5" diagonal piece in the middle of the antenna that is connected to the center conductor of the cable (and not grounded). This seems counter-intuitive to me that this would work. Can someone explain this in layman's terms?
 
The 2.5” piece that is connected to the coax is half of a parallel plate capacitor. Hook up a battery there, and the plate will acquire a charge. And the opposite side, an equal but opposite charge. Apply an AC voltage to the plate, and an opposite alternating charge is induced on the opposite side. In essence, the capacitor passes an AC current thru it. The antenna itself is ‘resonant’. Ever watch two kids, wiggling a rope between them up and down? If they do it just right, they can produce a ‘node’ in the middle. That is, the rope doesn’t move at all there, while there are large up and down oscillations at their hands. In the Archer antenna, there are large voltage oscillations at the far, open end. But at the end close to the feed line, there is a node: the voltage there is zero, unchanging. Since the voltage is zero it does no harm to connect it to ground, since it’s already at zero volts, no current will flow. You could disconnect it from the ground leg if you wanted, but it conveniently provides mechanical support.
 
The 2.5” piece that is connected to the coax is half of a parallel plate capacitor. Hook up a battery there, and the plate will acquire a charge. And the opposite side, an equal but opposite charge. Apply an AC voltage to the plate, and an opposite alternating charge is induced on the opposite side. In essence, the capacitor passes an AC current thru it. The antenna itself is ‘resonant’. Ever watch two kids, wiggling a rope between them up and down? If they do it just right, they can produce a ‘node’ in the middle. That is, the rope doesn’t move at all there, while there are large up and down oscillations at their hands. In the Archer antenna, there are large voltage oscillations at the far, open end. But at the end close to the feed line, there is a node: the voltage there is zero, unchanging. Since the voltage is zero it does no harm to connect it to ground, since it’s already at zero volts, no current will flow. You could disconnect it from the ground leg if you wanted, but it conveniently provides mechanical support.
Bob - you just reminded me why I switched from Electrical Engineering to Petroleum Engineering so many years ago! :D
 
KISS

Ever watch two kids, wiggling a rope between them up and down? If they do it just right, they can produce a ‘node’ in the middle. That is, the rope doesn’t move at all there, while there are large up and down oscillations at their hands.

This is the kind of example which inspires. My dad had the ability to do this. Sure miss him.

Thanks Bob!

Mike
 
Ummmmm, yeah. It just works. I don't understand how television works either, but I know how to hook it up and turn it on. I just followed the instructions on my Archer antenna and it worked as advertised.

My two cents of advice is don't go too far down the rabbit holes.
 
<off topic>

I was all-in on antenna theory and ham radio stuff in my youth (I still have my 1969 copy of the Radio Amateurs Handbook), but then I received the January 1975 edition of Popular Electronics in the mail and my life changed forever.

I gave up Smith charts for OpCodes and I've never looked back. Too bad, because antenna black magic would have been a good skill to develop. I'm happy just to buy an antenna and hope it works as advertised!

Note: I still have the Pop 'Tronics magazine in a ziplock bag! Google it.
 
Bob Archer Antenna

I talked to Bob Archer myself when he was alive and I still did not not understand how the NAV antenna works, but it does not matter because mine works great on my RV10. Just be careful to install it exactly as directed and make sure the edge that is to be grounded is grounded very well.

I can’t explain what goes on in all the magic boxes in my panel even though I installed 3 Dynon HDX screens and a Garmin GTN650 among other things. What matters is that they work and I know how to use them to fly IFR quite easily.

As an old Air Force friend told me, everything that goes on inside the magic boxes is either AM or FM (Another Miracle, or * Magic)
 
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