Ian, misguiding learners, undermining the foundations of radio education, is
my main objection to the ill-educated do-gooder discussions which take place
on this newsgroup.

Although at first I really did suspect your typist had made a translation
error between your dictation and her keyboard, I now see you insist you were
right first time.

You said -

No - I meant exactly what I said. The meter can only
indicate the rho/SWR of whatever is connected
downstream (load side) of the meter itself.


Ian, this statement will mislead and undermine students of radio for the
remainder of their careers. (You were one yourself.)

For their (and your) benefit it must be stated the so-called SWR/Rho meter
will indicate NOTHING about what lies on the antenna side of it EXCEPT,
indirectly, the magnitude RELATIVE to 50 ohms of the INPUT IMPEDANCE the
meter immediately sees looking towards the antenna.

Obviously, the impedance seen by the meter is that which, at HF, terminates
the other length of line, if one exists, between the transmitter and meter.

If, AND ONLY IF, the transmitter-to-meter line is 50-ohms then the 50-ohm
meter will indicate |Rho| relative to 50-ohms at the meter end of that line.
If the line is not 50-ohms then, although the meter may indicate SWR =1 or
Rho = TLI = 0, the transmitter will be loaded with something different from
50 ohms. Highly unsatisfactory!

The impedance of this line must NOT be neglected, as somebody said, on the
grounds that it forms part of the source impedance as seen by the meter, and
can be treated like the internal resistance of the transmitter as
irrelevant.

Alternatively, if the 50-ohm Tx-to-Meter line is long enough then that's the
line the meter indicates the SWR on. It is common knowledge SWR/Rho
determinations MUST begin by determining the value of the reflection
coefficient at the point where the reflection originates. ie., where the
meter is located along the uniform length of line.

The G5RV demonstrates the meter is ignorant of what may be happening on the
antenna side of the meter. Whatever the meter indicates it will NOT
correspond to |Rho| or SWR on the antenna's high-Zo balanced feedline. But
that's OK. Nobody wants to know anyway.

(Sooner or later someone will re-discover the special case that when the
transmission system is 50 ohms all the way from Tx to antenna, the meter
appears to measure |Rho| in both directions. This is because |Rho| is
sensibly constant in magnitude along the whole line. Actually |Rho| is
indicated looking back towards the transmitter and, by reversing the meter
in the line, thru-power is indicated looking towards the antenna. This
special case is the norm at UHF where line and connector dimensions are
critical and engineering economics force simplifications, including
simplification of underlying formulae. Chains of matrix algebra fit very
nicely into number-crunching computer software.

Now expect sombody who is still missing the point to say "not if the line is
1/2-wavelength long." But who wants a half-wavelength of line on 1.9 MHz
between the transmitter and swaarrr meter.
----
Reg, G4FGQ