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Q & A: Transmission of an A/C voltage along a cable

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Most recent answer: 08/03/2012
Q:
Starting with a 350' length of coaxial cable rated at 75 ohms impedence and connecting 19.2 volts A/C at one end, what is the output voltage at the opposite end of the 350 foot cable?
- Roger Langkamp (age 48)
Eau Claire, WI USA
A:
This is not a trivial question and cannot be answered with a simple answer. It depends on a number of variables that you have not specified including the termination impedance, the ohmic attenuation, the frequency of the signal, etc.   If there are no resistive losses and the cable is terminated with 75 ohms then the end voltage is the same at the input voltage.   If the cable is unterminated then the end voltage is twice that.   If the cable is terminated with a short then the voltage is, of course, zero.   In general if the cable has an impedance of Z1 and is is terminated with an impedance of Z2 the the output voltage will be Vout = Vin * 2Z2/(Z1+Z2).  Ohmic losses, that may be frequency dependent, further complicate the matter.

LeeH

(published on 08/03/2012)

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