With respect, it's not the end of the story - the generator *can't*
always have been delivering all it could to an optimum load if that load
changed with differing line conditions.
Let me take an extreme example to make the point.
Let's say that, when dry and in the clear, the line Zo is 450 Ohms and
the tuner is adjusted so that is effectively out of circuit. That means
the line is matched, and the signal generator sees 50 Ohms and delivers
its maximum power. We make a measurement on the microvoltmeter.
Now we drop the line onto the soil - let's say the Zo of the line halves
to 225 Ohms. We adjust the tuner so that the line remains matched; the
generator then sees a load of 25 Ohms and its output will drop by 0.5dB.
So the change we would measure at the microvoltmeter is 0.5dB plus or
minus any change in line loss. The problem we have is that, unless we
know that new value of Zo, we can't separate out the change due to
source mis-match loss from the change in line loss.
In practice if we simply adjust the tuner for maximum on the
microvoltmeter, all we know for sure is that we have minimised the sum
of the line loss and the source mis-match loss; under those conditions
we don't know that the line is actually matched - in fact it most likely
I would concede that if the changes in Zo are small, the generator
mis-match losses may be negligible, but I have no idea what sort of
changes in Zo you experienced; I wonder if you measured them?
On 27/01/2012 22:44, Joel Hallas wrote:
> Well keep in mind that everything here is close to being matched. The
> generator was delivering all it could to the optimum load that was presented
> to it. Think transmitter - transmission line - tuner - antenna.
> End of story.
> Regards, Joel Hallas
> Westport, CT
> -----Original Message-----
> From: email@example.com [mailto:firstname.lastname@example.org]
> On Behalf Of Steve Hunt
> Sent: Friday, January 27, 2012 5:24 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Re. [Ten Tec] Grounds and balanced fed verticals
> Then that puzzles me even more !
> If you made a change to the line and then adjusted the single tuner at
> the load end, the impedance terminating the line changed. If the
> terminating impedance changed and the line remained matched, the load
> seen by the generator changed. If the load seen by the generator changed
> then so did the power it delivered to the system.
> That suggests that some of the level change measured on the
> microvoltmeter might have been due to variation in generator output
> rather than changes in line loss. It seems to me that another tuner at
> the source end would be essential to ensure that the generator always
> "sees" 50Ohms, and always delivers the same power to the line.
> Or did I misunderstand something?
> Steve G3TXQ
> On 27/01/2012 21:47, Joel Hallas wrote:
>> I stand corrected, my memory is good but short<g>. I went back and looked
>> at the article. The single tuner was at the far end. That did make it
>> to adjust it while looking at the uW meter. At maximum output, it still
>> reflected an impedance back to the generator that provided maximum output.
>> Regards, Joel Hallas, W1ZR
>> Westport, CT
> TenTec mailing list
> TenTec mailing list
TenTec mailing list