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Does the length of Transmission line between source and load matter?

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sdmuashr

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Hi,
If the source is connected to the load in such a way that maximum power is transferred to the load. And now if I change the length of transmission line between source and load then the maximum transmission of power is still possible or not? Also if I change the phase of S11 of the line between source and load then what would happen?
 

If the line impedance is the same as the load impedance, the only thing that matters is the loss in the line. If the impedances are different, use a length of line that makes the real part of the line input impedance what you want and cancel the imaginary part of the input impedance with a coil or capacitor.
 

sdmuashr said:
Hi,
If the source is connected to the load in such a way that maximum power is transferred to the load. And now if I change the length of transmission line between source and load then the maximum transmission of power is still possible or not? Also if I change the phase of S11 of the line between source and load then what would happen?
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line loss is VERY significant and gets more so as the frequency increases or length of transmission line increases with a given frequency
so, for example there are many different coax cable types that are designed to give lower losses at a given freq than other types
a real example ... 1296MHz ( one of my amateur radio bands) 20 metres of LMR 400 cable will have a loss of ~3dB over that length .... 20W in one end and 10W will appear at the other end

Dave
 

Changing ONLY the phase at the output of the PA can be harmful, the same as increasing the VSWR or the loss, especially for high-power amplifiers.
Even perfect impedance matched and loss-less transmission line it will introduce inevitably a phase shift in the circuit.
 

With the case of a transmission line between a source and a load there always are the following important points:
1. Matching the load to the line,
2. line loss as a function of its length
3. matching the load to the line
4. homogeneity of the line

In general, even with a good line, small mismatches of the source and load cause reflections and a standing wave forms in the line.The longer the line , then more loss is seen due to its loss as well as due to the standing wave.

At microwaves, instead of coaxial line waveguides are preferred due to much lower loss. The line , source and load properties combine also to their frequency variation; some loads vary also due to signal power.
 

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