On 10/5/2015 5:43 AM, Roger Hayter wrote:
rickman wrote:

On 10/5/2015 4:17 AM, Ian Jackson wrote:
In message , rickman writes



You keep saying that the 1:1 match between the TX and the ATU prevents
any power from being sent to the TX which is not true. You are
confusing the power from the TX which is not reflected and the power
reflected from the antenna which passes through the ATU to the TX.

If the SWR meter between the TX output indicates a 1:1 SWR, then there
can be NO power travelling between the ATU input and the TX output - ie
there IS no reflected power. QED, surely?

If you ignore the losses in the ATU, all the power that the mismatched
antenna reflects, and that makes it back to the ATU output, MUST be
re-reflected by the ATU output impedance, and head off back towards the
antenna. This is because the reflected signal cannot heat up a lossless
ATU, and the SWR meter says it isn't coming back through the ATU. It
simply has nowhere to go except back down the coax.

You saying something is true or imagining a SWR reading is not the same
as understanding what is going on. What SWR reading are you imagining?
Can you explain this in terms of the circuit analysis? The ATU
consists of what circuit? The TX has some source impedance, what would
that be? I don't think you can design an ATU circuit that will isolate
the real source impedance of the TX from the reflected wave from the
antenna.

So, when you tune your transmitter-end ATU for minimum SWR *between the
Tx and the ATU*, what exactly are you doing? You are making the
feeder/aerilal/ATU combination look like a resistive load from the
transmitter side, what are you making the ATU/transmitter combination
look like from the aerial feeder side? It must be something that
reflects back incident waves, otherwise your SWR meter wouldn't be
reading 1.0. That seems to be the argument, and it sounds moderately
convincing to me.

I don't know what you are doing. I am talking about analysis of the
circuits involved. If analyzing the circuits is not appropriate we can
just drop this discussion.

Any chance of coming up with a specific circuit? Forget tuning, let's
set parameters for the TX, cable, antenna, calculate the circuit for the
ATU and then we can see what happens at the various interfaces.

--

Rick