"Roy Lewallen" wrote in message
...
This has been explained many times, to no avail.

So instead of one of us explaining it yet again, I suggest that you do
the following experiment. It requires only a transmitter, one or two
dummy loads, an SWR meter, and no more than five minutes of your time.

1. Connect the transmitter to either a dummy load or an antenna through
the SWR meter and measure the SWR.

2. Connect the transmitter in parallel with a dummy load by using a tee
connector. Connect this parallel combination to the input of the SWR
meter, and the output of the SWR meter to the same load as before (dummy
load or antenna).

If you don't have 2 dummy loads, there is a simple alternative. Connect the
TX to the meter through a 1/4 wave section of 75 Ohm line. Unless the TX
output was 75 Ohms, the equivalent TX output impedance seen by the meter has
changed.

Tam/WB2TT

Do you see any change in the SWR?

If you don't, then something is wrong with your theory -- since the
source impedance is clearly different for the two measurements --, and
you should take the effort of resolving it with your recent observations.

Roy Lewallen, W7EL

Richard Fry wrote:
"Ian White, G3SEK"wrote:

Richard Fry wrote:

"Ian White, G3SEK wrote

The meter measures nothing that involves the source, except
the level of RF that it supplies. It does not respond in any way
whatever to the source impedance.

Not that I said it did in my part of the thread, but nevertheless the

above

statement is not strictly true. In the case where the source Z of the
tx

PA

does not match its load Z (which is typical), power reflected from the

load

mismatch will at least partly be re-reflected from the PA -- which then
contributes to the power sensed by a "wattmeter" in the output path.

Sorry, that statement cannot be correct. It would mean that the
impedance you measure at the near end of a transmission line (terminated
by some arbitrary load at the far end) would depend on the internal
impedance of the device that's doing the measuring - and that is not
true, either in transmission-line theory or in the real world. It is a
function only of the line and the load. etc

____________

How, then, do you explain the "ghost image" that can occur* in
analog(ue) TV
transmission systems arising from reflections at/near the antenna end of
the
station's transmission line?

*with sufficient round-trip propagation time in the transmission line

RF