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this post was submitted on 08 Jun 2024
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If you don't mind a followup question, what's happening when a signal clears up if you touch or just hover near an antenna?
possibly several things but my first thought is your body is acting like a capacitor to ground. I'm guessing you've noticed this on an FM radio or rabbit ears on a TV that probably weren't grounded well.
That can be for a few reasons...
In some cases you're tuning (or detuning) the antenna capacitively.
On other cases, like if your tv gets interference when you're standing in part the room, there may be standing waves causing interference, as the rf is bouncing around your room.
To further your point, theorically, there is a voltage potential between any two objects. That's the capacitance. Better conductor, for the same surface area, create a bigger potential.
So when you tune/detune a signal with your presence near the antenna, it is because you are close enough to the antenna that the potential between you and the antenna affects the filter of the signal.
Sorry, your comment doesn't make sense and doesn't seem correct to me.
Yes there is a capacitance, but capacitance isn't "voltage potential". Capacitance is a ratio of coulombs per volt. Anyway, that's beside the point.
There is capacitance and it's defined by geometry.
"The potential between you and the antenna affects the filter of the signal"
You're not adding potential to anything, nor are you affecting any filters.
Any capacitance you add will change the impedance of the resonant antenna. You get maximum power transfer when the impedance is matched.
Another way to look at it, you're changing the resonant frequency.
How do you think you are changing the resonant frequency? By modifying it's capacitive impedence, i.e. creating a capacitor with yourself and the antenna.
And you know what we call the difference of electric potential between two points? Voltage.
When you say that capacitance is geometry, you are right. The distance between two objects, be it you and an antenna or two planks of wood, affect the capacitive impedance.
... Was this written by ai
I'm an rf engineer and I swear it feels like I'm having a stroke reading your comments
As the distance increase between two surfaces, the capacitance diminishes and the voltage between the two increase, so that C=QV is always true.
The resonant frequency is determined by the impedence, i.e. capacitive and inductive impedence.
You can't affect inductive impedance of the antenna because you are not a coil and do not emit EMR. But you can change the capacitance between you and the antenna by moving closer or further away.
as the distance increases the capacitance reduces. But C=Q/V doesn't mean you're not inducing any potential into the antenna... You're adding to the load... C=ε*A/d is the equation that says capacitance will decrease with distance, but that isn't going to induce any voltage in this case.
yes this is what I'm saying.
in the very near field, conductive tissue, ie a body, will have Eddy currents. Your body has an ε term as well as σ. You can definitely load an antenna. The R term will dominate but there will be some effect on inductance.