Hello,
I'm taking a course on electromagnetic compatability and having trouble with one of the homework problems. The instructor does not collect any of the homework so this is not a for credit assignment. The book also gives the answer to the problem, I just can't seem to get the same answer. The instructor doesn't answer questions during class and unfortunately I cant make his office hours. I can contact him by email, but I thought I might try here first.
Heres the problem from the book "Introduction to Electromagnetic Compatibility" by Clayton R. Paul.
1.17 A 50 ohm oscillator is attached to the high-impedance input of an oscilloscope (Cin = 47pF, Rin= 1Mohm). The source is tuned to 100Mhz and the level set to -30dBm. Determine the voltage level (peak) of the sinusoid seen on the oscilloscope face.
Answer given in book: 11.22 mV
My approach based an example in the book:
The source assumes a 50 ohm load, so first I determined the open circuit voltage of the source.
Vout = sqrt(50*Pout) = sqrt(50*.000001) = .007071 Vrms
Voc = 2*Vout = .01414 Vrms
Vocpeak = 1.414*Voc = .019997 Vpeak
I then determined the input impedance of the load.
Xc = 1/(2*pi*f*c) = 1/(2*pi*100E6*47E-12) = 33.86 ohms
This is in parrallel with the 1Mohm, which doesn't change value to this precision.
The voltage seen at the scope could then be calculated by using a voltage divider.
Vscope = Vocpeak * 33.86/(33.86+50) = .00807 Vpeak = 8.07 mVpeak
I also tried calculating the open circuit voltage using the power of -30dBm going into a 33.86 ohm load and a 83.86 ohm load, but that doesn't help either.
Can anyone give me an idea of where I am going wrong?
Thanks,
Jamey
I'm taking a course on electromagnetic compatability and having trouble with one of the homework problems. The instructor does not collect any of the homework so this is not a for credit assignment. The book also gives the answer to the problem, I just can't seem to get the same answer. The instructor doesn't answer questions during class and unfortunately I cant make his office hours. I can contact him by email, but I thought I might try here first.
Heres the problem from the book "Introduction to Electromagnetic Compatibility" by Clayton R. Paul.
1.17 A 50 ohm oscillator is attached to the high-impedance input of an oscilloscope (Cin = 47pF, Rin= 1Mohm). The source is tuned to 100Mhz and the level set to -30dBm. Determine the voltage level (peak) of the sinusoid seen on the oscilloscope face.
Answer given in book: 11.22 mV
My approach based an example in the book:
The source assumes a 50 ohm load, so first I determined the open circuit voltage of the source.
Vout = sqrt(50*Pout) = sqrt(50*.000001) = .007071 Vrms
Voc = 2*Vout = .01414 Vrms
Vocpeak = 1.414*Voc = .019997 Vpeak
I then determined the input impedance of the load.
Xc = 1/(2*pi*f*c) = 1/(2*pi*100E6*47E-12) = 33.86 ohms
This is in parrallel with the 1Mohm, which doesn't change value to this precision.
The voltage seen at the scope could then be calculated by using a voltage divider.
Vscope = Vocpeak * 33.86/(33.86+50) = .00807 Vpeak = 8.07 mVpeak
I also tried calculating the open circuit voltage using the power of -30dBm going into a 33.86 ohm load and a 83.86 ohm load, but that doesn't help either.
Can anyone give me an idea of where I am going wrong?
Thanks,
Jamey