I'm using the AA-55 ZOOM to trim RG11 coax to an electrical length of a halfwave at 3500 kHz. The stub tuner tool shows the current length as being a halfwave at around 3560 kHz with the far end open circuit but the RC chart tool shows the resonance (where the reactance sign changes polarity) as being around 3540 kHz with either an open or short circuit at the far end. Any thoughts on why am I seeing this much variation between the different tools within the analyser? Which tool can I rely on to give the most accurate result in this situation?

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Sorry - I meant to say that the stub tuner tool displays 3460 kHz and the RX chart displays the resonance at 3540 kHz, I.e. a difference of 90 kHz. So which one is more correct?

On Tue, Mar 9, 2021 at 05:50 AM, Brian Miller wrote:

Sorry - I meant to say that the stub tuner tool displays 3460 kHz and the RX chart displays the resonance at 3540 kHz, I.e. a difference of 90 kHz. So which one is more correct?

When you measure a stub you need to use a short circuit at the end for half-wavelength and open circuit for quarter wavelength.? This gives the steepest transition for X and the correct result.? This is described on page 18 of the user manual but unfortunately not in the Stub tool section or on the analyzer itself.??



I did some measurements of on a 31 foot piece of RG-58.? Here are the results using the RX method and the Stub tool method

RX measurement:
-? Quarter wavelength frequency = 4.987 MHz. with open circuit at end? ** correct method
-? Quarter wavelength frequency = 4.981 MHz. with short circuit at end?

-? Half wavelength frequency = 10.009 MHz. with open circuit at end
-? Half wavelength frequency = 10.034 MHz. with short circuit at end? ? ???** correct method

Stub tool measurement:
-? Quarter wavelength frequency = 4.987 MHz. with open circuit at end? ** correct method
-? Quarter wavelength frequency = 4.981 MHz. with short circuit at end?

-? Half wavelength frequency = 10.133 MHz. with open circuit at end
-? Half wavelength frequency = 10.038 MHz. with short circuit at end? ? ???** correct method

You will note both techniques give the same answer to with in a few hertz. when terminated correctly.??

ATTN. RigExpert support -??I was using beta firmware 1.26 to do these tests.? It occasionally stopped scanning and froze when using the Stub Tool with no results screen displayed.? After displaying the final values it always crashed with a flashing screen and I had to power off the AA-55 Zoom and power back on to get to the main menu.? I don't know if it does this with previous versions of the firmware.? Perhaps other users can comment on this bug.

Doug VE7DXK