[TenTec] Re. [Ten Tec] Grounds and balanced fed verticals

[Steve Hunt]

Joel,

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 
wont be.

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?

73,
Steve G3TXQ




On 27/01/2012 22:44, Joel Hallas wrote:
> Steve,
>
> 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: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
> 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
>
> Joel,
>
> 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?
>
> 73,
> Steve G3TXQ
>
> On 27/01/2012 21:47, Joel Hallas wrote:
>> Steve,
>>
>> 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
> easier
>> 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
>>
>>
>>
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