question about tuning stubs.

[obrien135]

A long time ago I had to do an analysis to determine whether it was feasable to use tuning stubs to balance a transmission line. As I recall, the reactive component was dependant on the length of the line with respect to the wavelength. How does cable capacitance figure in, and why is it ok just to terminate the receiver with an impedance equivelent to the cable ans output impedance if it is dependant on the length of cable? Is that only true if using unmatched impedances?

George

 

[drfaustus]

A long time ago I had to do an analysis to determine whether it was feasable to use tuning stubs to balance a transmission line. As I recall, the reactive component was dependant on the length of the line with respect to the wavelength. How does cable capacitance figure in, and why is it ok just to terminate the receiver with an impedance equivelent to the cable ans output impedance if it is dependant on the length of cable? Is that only true if using unmatched impedances?

George

Cable capacitance is capacitance per unit length. It determines the characteristic impedance of the transmission line (cable). Impedance matching demands that the load of a transmission line must equal the characteristic impedance of the feeding cable in order to establish maximum power transfer. In the case of a receiver this is not as critical as with transmitters. Impedance matching at the receiver input can be used for VSWR flattening but the feeding transmission line should have a low VSWR itself.

 

[RCinFLA]

If what you mean by balancing is taking an unbalance coax to balance line, attached is a diagram of how to make one that does unbal to balanced and does impedance matching.