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Bob, this has helped me to understand what conditions cause impedance transformation however, I'm still trying to figure out the "why" behind it all. It appears that impedance transformation only takes place when the transmission line does not match the source impedance.

I say this because I can change the length of 50 ohm coax and the resistive load at the end of the cable and as long as the cable is 50 ohms, the MFJ was able to accurately read the value of the carbon resistor even when that resistor was 100 ohms.

As soon as the cable was changed to 75 ohms the only length that read the load resistor properly were 1/2 wave multiples. All other lengths caused impedance transformation and change in VSWR. The problem here is I already know I can change source impedance without it effecting the VSWR.

Which brings me to the question, why does impedance transformation take place when the cable is 75 ohms and does not match the source, but not when the load doesn't match the cable or when the source impedance is changed? I see what works now as far as causing an impedance transformation however, I feel no closer to understanding the "why" behind it.

I'd like to assume it's simply because I'm using a 50 ohm MFJ instrument on a 75 ohm cable but this implies we are just tricking the meter and that does not line up with accepted theory that 75 ohm cables can be used to change impedance.

<blockquote data-quote="Shockwave" data-source="post: 434434" data-attributes="member: 10882">Bob, this has helped me to understand what conditions cause impedance transformation however, I&#039;m still trying to figure out the &quot;why&quot; behind it all. It appears that impedance transformation only takes place when the transmission line does not match the source impedance. I say this because I can change the length of 50 ohm coax and the resistive load at the end of the cable and as long as the cable is 50 ohms, the MFJ was able to accurately read the value of the carbon resistor even when that resistor was 100 ohms.As soon as the cable was changed to 75 ohms the only length that read the load resistor properly were 1/2 wave multiples. All other lengths caused impedance transformation and change in VSWR. The problem here is I already know I can change source impedance without it effecting the VSWR.Which brings me to the question, why does impedance transformation take place when the cable is 75 ohms and does not match the source, but not when the load doesn&#039;t match the cable or when the source impedance is changed? I see what works now as far as causing an impedance transformation however, I feel no closer to understanding the &quot;why&quot; behind it.I&#039;d like to assume it&#039;s simply because I&#039;m using a 50 ohm MFJ instrument on a 75 ohm cable but this implies we are just tricking the meter and that does not line up with accepted theory that 75 ohm cables can be used to change impedance.</blockquote>

[QUOTE="Shockwave, post: 434434, member: 10882"] Bob, this has helped me to understand what conditions cause impedance transformation however, I'm still trying to figure out the "why" behind it all. It appears that impedance transformation only takes place when the transmission line does not match the source impedance. I say this because I can change the length of 50 ohm coax and the resistive load at the end of the cable and as long as the cable is 50 ohms, the MFJ was able to accurately read the value of the carbon resistor even when that resistor was 100 ohms. As soon as the cable was changed to 75 ohms the only length that read the load resistor properly were 1/2 wave multiples. All other lengths caused impedance transformation and change in VSWR. The problem here is I already know I can change source impedance without it effecting the VSWR. Which brings me to the question, why does impedance transformation take place when the cable is 75 ohms and does not match the source, but not when the load doesn't match the cable or when the source impedance is changed? I see what works now as far as causing an impedance transformation however, I feel no closer to understanding the "why" behind it. I'd like to assume it's simply because I'm using a 50 ohm MFJ instrument on a 75 ohm cable but this implies we are just tricking the meter and that does not line up with accepted theory that 75 ohm cables can be used to change impedance. [/QUOTE]

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