Transmission Line Question

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WA4WAX:
I can help with this one.

Assume you have a Johnson Matchbox feeding a 105 ohm loop with a length of 450 ohm ladder line.  The box is adjusted to give 50 ohms at the input.

When the reflected wave reaches the match point inside the box, 100% of it is reflected back towards the antenna.  That is where rho = 1 comes from.  When you look in the input, rho = 0, assuming a 50 ohm transmitter.

So, he is talking about rho for two different points in the circuit.

ashart:
To:  WA4WAX

Well!  That certainly explains how rho can be 0 in Chapter 3 and 1 in Appendix 7!  I never thought of his referencing two different points!  Thank you!

Might you have time to address a follow-on question?

How can one define a “match point” within a hypothetical tuner, be it L or T, and absent a tuner, where within a PI tank or a link-coupled tank, would one find that match point?

Thank you again!

-al hart
al@w8vr.org

WD8BIL:
It still doesn't add up.

According to ; Quote

ñ =  [ Z(load) - Z(line ] / [ Z(load) + Z(line) ]
, if there is a match Z(load) - Z (line) = 0. Therefore p=0 and there is no reflection.

Steve - K4HX:
Only true on the transmitter side of the tuner.

WD8BIL:
What if there is no "tuner"? If the source and line are matched at the source end, and a mismatch is present at the load end the resulting reflected wave will see p=0 at source. The source will then have to absorb/dissipate the reflection, right?

Now I can see, with a tuner you actually have 2 systems working here. 1 source/line/load system from radio to tuner and one source/line/load system from tuner output to load. In the second case the tuner will then have to deal with reflection when tuned to a match and p again =0.

Confusing stuff.

But to Al's original observation:

If p =  [ Z(load) - Z(line ] / [ Z(load) + Z(line) ] is true, and Z (load) = Z (line) then the numerator will =0 and p cannot equal 1. Therefore the statement; "On arriving at the line input it sees total reflection ñ = 1 at the matching point in the network that achieved the conjugate match” cannot be true.



 

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