Antenna analyzer vs feedline type
|Sep 21st 2012, 14:37|
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Total Posts: 0
A member asks:
I have a 20M dipole fed with about 100 feet of windowline. The feedline (windowline) has a 12 inch length of coax at the end that connects to the radio. I would like to get an antenna analyzer to see how well my system is working. My question is: will an antenna analyzer give accurate readings with the windowline used for a feedline or is it only good with coax for the feedline.
An antenna analyzer uses directional couplers that are most accurate when terminated with a characteristic impedance of 50 ohms. What a clever ham could do is to vary the length of the window line to bring the impedance close to 50 ohms, and terminate it a 1:1 balun. You can then use a program like Transmission Line for Windows to calculate the input and output impedances for any transmission line length--it comes with the ARRL Antenna Book.
True, you won't be able to bring down the impedance if the impedance is closely matched to the window line impedance, but if that is the case, you now know that the impedance is close to the window line impedance.
Zack Lau W1VT
Senior Lab Engineer