fundomental question in telecommunication circuit

[baby_1]

fundamental question in telecommunication circuit

Hello
according the our studies we now for working a circuit the circuit should be close for moving current.now how a reciver antenna works? the antenna doesn't close to flowing electron in circuit??!!!!

 

[flatulent]

The current goes back and forth. There is no net DC current.

 

[baby_1]

Thanks flatulent
could you let me now more?
1-according your explanation it doesn't Induction any charge to our antenna?
2-when i was designing a simple am transmitter with 555 i see that when my antenna it open about 50cm and doesn't connect any where it has 1volt(VP-VP)(i checked my my osciloscope) how can it has?

 

[E Kafeman]

Last time I checked was my antenna a closed circuit with a measurable impedance.
Better with current that goes forth, reverse current (reflections) causes poor antenna efficiency.

 

[baby_1]

Thanks E Kafeman
but i want to know this contradiction in kirshohf law

 

[E Kafeman]

I do not see any problem with Kirchhoff's volt and current laws as long as you remember that in RF are both voltage and current vector values.
If you is asking how to calculate received energy for an antenna, can this be a good start: https://physics.info/em-waves/

Your 555 TX example, is a bit special as TX and RX monopole antennas had a very short distance between each other compared to RF wavelength. In that case can you see it as each antenna is a part of same capacitor so you can replace both TX and RX antenna with a single serial capacitor between transmitter and oscilloscope and getting same result.
If coupling effect is good between your antennas should summing of all currents and voltages in the LM555 circuit and oscilloscope show that Kirchhoff was right but due to nature of EM waves would a minor amount of energy radiate in other directions where it can be hard to measure. Same experiment repeated in a metallic chamber can reduce these losses.