Rick,
We are talking about sweeping the feedline and looking at the REAL R sweep vs
frequency….NOT impedance Z=R+jX.
We are looking for relative dip in R, not absolute values. We are looking to
see at what frequency this dip occurs.
If I put a 25 ohm resistor and then a 50 ohm resistor at the end of a 55 degree
feedline, are you saying the real R (not Z…no X) will read 50 ohms in both
cases? I think my multimeter would say something different at DC.
If this is true, then you are correct, and the dip in the real resistance seen
at the driver at the parsitic frequency would be muted….the sweep would be
flatlined at 50 ohms across the frequency of interest.
de steve ve6wz
> On Apr 26, 2020, at 12:35 PM, Richard (Rick) Karlquist
> <richard@karlquist.com> wrote:
>
>
>
> On 4/23/2020 7:40 PM, VE6WZ_Steve wrote:
>> Tom,
>> Yes.
>> Just sweeping from the end of the coax in the shack should show the same dip
>> of R at the correct frequency.
>> (The absolute R value (in Ohms), and X value will not be correct because of
>> the feedline transformation, but the frequency of the R dip is ONLY a
>> function of the reflector tuning.) Try it and see.
>
> I don't see how this would be true for an arbitrary length
> of coax, especially if it is an odd multiple of a quarter
> wave. For example, if the load on the far end changes
> from 50 ohms to 25 ohms, the analyzer in the shack will
> see resistance INCREASE from 50 to 100 ohms. A line with
> electrical length of 55 degrees will have a resistance
> at the shack of 50 ohms whether terminated in 50 ohms
> or 25 ohms.
>
> 73
> Rick N6RK
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