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Solid States Devices => Wireless Energy Transfer => Topic started by: erfandl on June 08, 2020, 11:28:59 AM

Title: short circuit frequency ?
Post by: erfandl on June 08, 2020, 11:28:59 AM
Hi everyone. I have a question about short circuit and the AC/at given frequency. does the AC/ at given frequency change when the short circuit occurs? if yes how much the frequency changes ?

thanks.
Title: Re: short circuit frequency ?
Post by: Thaelin on June 08, 2020, 11:51:35 AM
See Antenna Theory.
Title: Re: short circuit frequency ?
Post by: erfandl on June 08, 2020, 02:53:06 PM
What does it have to do with the antenna? :|
Title: Re: short circuit frequency ?
Post by: Thaelin on June 09, 2020, 03:53:54 PM
I am refering to what happens to a sine wave on an antenna shorted cable. It has reflections back to the source.


thay

Title: Re: short circuit frequency ?
Post by: stivep on July 08, 2020, 10:08:44 PM
Hi everyone. I have a question about short circuit and the AC frequency. does the AC frequency change when the short circuit occurs? if yes how much the frequency changes ?

thanks.


Answer for piece of coaxial cable known as transmission line that is shorted open or terminated at the end:
No it will not change
.. however it may..cerate transients
it will not change in transmission line but if that  length of the cable represents resonating circuit while  having  LC reactive character than it may also  act as a "mixer" creating by-products.
but hm........ I have never thought  about it....

https://patents.google.com/patent/US5142697A/en
 (https://patents.google.com/patent/US5142697A/en)https://www.rf-microwave.com/en/mini-circuits/zfm-2h-s/rf-coaxial-mixer-sma-female-connectors/zfm-2h-s/ (https://www.rf-microwave.com/en/mini-circuits/zfm-2h-s/rf-coaxial-mixer-sma-female-connectors/zfm-2h-s/)


when  the coaxial cable  that is connected to OUT of Tx ( transmitter) is shorted it is the  same ( well not  the same but close) as if  there  was no   load connected to its end or the cable was open.
That means  nothing connected to PL or BNC connector at the end of it.

but there is more than that:
 The nature of that reflection depends on how the cable is terminated at the other end.
Shorting the cable at the far end produces an inverted reflection. With no termination (an "open" end),
the reflected pulse is not inverted.
When the impedance of the termination matches that of the cable, there is no reflection.


other  important factors :impedance of the cable, the output impedance of the signal source, the length of the cable, etc.
https://eng.libretexts.org/Bookshelves/Electrical_Engineering/Electro-Optics/Book%3A_Electromagnetics_I_(Ellingson)/03%3A_ (https://eng.libretexts.org/Bookshelves/Electrical_Engineering/Electro-Optics/Book%3A_Electromagnetics_I_(Ellingson)/03%3A_)
Transmission_Lines/3.16%3A_Input_Impedance_for_Open-_and_Short-Circuit_Terminations

Schort circuited transmission line.
https://www.daenotes.com/electronics/communication-system/short-circuited-transmission-line


 (https://www.daenotes.com/electronics/communication-system/short-circuited-transmission-line)answer #1
 for regular  short circuit:
https://en.wikipedia.org/wiki/Short_circuit (https://en.wikipedia.org/wiki/Short_circuit)


answer #2
 for regular  short circuit:
if  the circuit represents after  it is shorted a resonance circuit with its LC reactive components that  any frequency can resonate with it.
https://www.qsl.net/va3iul/RF%20Mixers/RF_Mixers.pdf (https://www.qsl.net/va3iul/RF%20Mixers/RF_Mixers.pdf)
The two signals inserted into the two input ports are usually the Local Oscillator
signal and the incoming (for a receiver) or outgoing (for a transmitter) signal.
To produce [/font]a new frequency or new frequencies requires a nonlinear device.
[/font]In a mixing process if we want to produce an output frequency that is lower
than the input [/font]signal frequency, then i[/font]t is called down-conversion and
if we want to produce an output signal that is at a higher frequency than the input signal,
it is referred to as up-conversion


Wesley
Title: Re: short circuit frequency ?
Post by: stivep on July 09, 2020, 02:37:14 AM
here is little better  explanation what is going on if e.g transmission line is shorted.
you are dealing with number of resonant circuits in that transmission line parallel and series .
https://www.daenotes.com/electronics/communication-system/short-circuited-transmission-line
http://www.eas.uccs.edu/~mwickert/ece3110/lecture_notes/N3110_2.pdf

Wesley
Title: Re: short circuit frequency ?
Post by: Smudge on July 09, 2020, 11:13:28 AM
Hi everyone. I have a question about short circuit and the AC frequency. does the AC frequency change when the short circuit occurs? if yes how much the frequency changes ?

thanks.

Could you please define what you are short circuiting?  I suspect that you are talking about transformers or mutual coupling between two coils, but without knowing what you are dealing with it is impossible to give an answer.

Smudge
Title: Re: short circuit frequency ?
Post by: stivep on July 09, 2020, 12:51:58 PM
I did, but you didn't  understand what I wrote.it was  the
Answer for piece of coaxial cable known as transmission line that is shorted open or terminated at the end:

the answer:
No  frequency  will not change
.. however it may..create transients.__________________________

In any short circuit :
- if mixing of products or byproducts   of LC reactive components  is not happening than frequency doesn't change.
________________________

think of it as:
1. you need  generating circuit to make generation of the signal
2. you need circuity to  process the signal
3. no matter what you do with this circuit - frequency  of already generated signal doesn't change.
However  we must exclude circuits purposely made by us and intended to change frequency of the signal by means of e.g mixing.
Mixing can  also happen by accident.

(FM modulation is one of examples of  frequency change)


Wesley
Title: Re: short circuit frequency ?
Post by: Smudge on July 09, 2020, 04:36:30 PM
Hi Wesley,

My question was not addressed to you, it was addressed to Erfandl who started this thread.

Smudge