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Re: Calibrating to a long coax?
#applications
#calibration
#measurement
REF: /g/nanovna-users/message/13681
Hello, again. Well, after the Special Interest shown here, we would like to inform you that, in direct contrast with what Gary O'Neil, N3GO believed on 2009-09-30 - in the "Errors of error models. Who is following this and who is confused" thread, at his message: /g/nanovna-users/message/3492 - that is that: "They appear to have done limited testing of their math model", there are plenty Measured Results by a VNA under these Most Interesting Extreme Conditions created by many Open- and Short- circuited loads, which were produced by purposely constructed for that reason Special Antennas, and we plan to present some of these results, as soon as possible, within the frame of discussion: "errors of "error" models". Sincerely, gin&pez@arg |
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Re: Calibration issue causing ripples in SWR?
#calibration
The 50 ohms cables as far as I remember were rated by different
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manufacturers as 50 to 52 ohms years ago, so my guess is that 51 ohms is on the ballpark. It is also a standard resistor value. Try to find out the cable impedance, it seems to me to be the culprit. Find the frequency where the cable is lambda/4 as a RF short circuit with the end of the cable physically open. Set half the frequency found before on the VNA and read the reactance, that is the cable?s impedance. I am writing by heart, a mistake might have slipped... Jos¨¦, CO2JA On 5/21/20, ed@... <ed@...> wrote:
After calibrating, I connected my nanovna to my VHF antenna via a brand new |
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Calibration issue causing ripples in SWR?
#calibration
After calibrating, I connected my nanovna to my VHF antenna via a brand new 75 foot length of 50ohm DX400MAX coax. The SWR measurement oscillates up and down every 4MHz or so (see attached). These correspond exactly to the half-wavelength harmonics of the cable. Looking at the smith chart, it is clear that the impedance is tracing a circle around about 45 ohms rather than the constant-SWR circle centered at 50 ohms, resulting in a frequency-dependent SWR.
Is there is a good way to determine whether this is a problem with my nanovna, with the calibration standard, or with the cable? One note: the calibration standard load measures 51 ohms DC resistance, which seems like a problem to me. Should my standard be exactly 50 ohms dc resistance? |
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Re: Reseting or proving that the new nanoVNA actually works
I think you need to explain "doesn't seem to be working." Does that mean that when you turn it on, absolutely nothing happens? Likewise, explain "don't get any results." Nothing appears on the screen? Also, "I would have thought that I should see something" needs further explanation. That implies that you see NOTHING. So, why don't you tell us what you are seeing? Which traces do you have turned on? Do any traces appear on the screen? Does the Smith chart appear on the screen? Are there any traces overlaying the Smith chart? If you are looking at return loss, or VSWR, for example, is there a line across the screen? If so, where is it? Top of the screen? Bottom of the screen? You say you have calibrated it a number of times, that implies that you are seeing something on the screen. What are you seeing? You really haven't given us anything to go on here.
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Re: Reseting or proving that the new nanoVNA actually works
The Nanovna-saver program has an issue where you can try and calibrate it
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and it doesn't work. Make sure you use the "calibration wizard" in the nanovna-saver program under the. You will soon learn to save the configuration file of commonly used setups. Robert M On Wed, May 20, 2020 at 1:29 PM billcoombes <bill@...> wrote:
My VNA doesn't seem to be working but occasionally, I can get a reading on |
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Re: Calibrating to a long coax?
#applications
#calibration
#measurement
Hello.
Let us ask, please, two "rhetorical" questions, which are addressed to all readers of this thread: - Is there anyone, ever, wondered, in any similar to this, under discussion, case - that is both "near by"- and "far away" from- a VNA: = (1) What is the behavior of the three "Traditional" measurement "errors" (ED, EM, ER) or (D, M, R) ? - We had; and found the following results [1][*]: - = (2) How much "the measurement errors are taking over" ? - We had; and found the following results [2][*]: - for two substantially different loads under the two, most typical, telecommunication situations, respectively, that is of: - a load "near by" a VNA - in fact, a DC-50-Ohm Resistor - and - an Antenna "far away" from that VNA - in fact, a Ground-Plane one. Well, from the last figure, any reader can easily see how much the Error of Measurement is, as: (a) A "Traditional", Absolute, Real Non-Negative, Error: Delta-S11, as it is calculated by using the technique introduced by HP and thus resulted as a couple of circles on the Complex Plane of this figure, as well as, (b) An Estimation of the Complex Core Uncertainty of the Measurement Error Delta-Rho, computed and drawn by using two methods [3]: a differential and a numerical one, and thus resulted as a continuous line and a cluster of points, respectively, on the Complex Plane of this figure. CONCLUSION Although, in comparison, these two Estimations of the Measurement Error have quite different appearance, because the Traditional Error is arbitrarily less or more than the Core Uncertainty Error, "near by"- and "far away" from- that VNA, respectively, the final judgement of which one of these two estimations represents more accurately the Measurement Error is left to the reader. Sincerely, gin&pez@arg REFERENCES [1][*] : Fig. 2 & Fig. 4 [2][*] : Fig. 13 [*] : [researchgate] : [3] : gin&pez@arg : [errors of "error" models"] : a thread, beginning with #2,770 : 2019-09-21: /g/nanovna-users/message/2770 |
gin&pez@arg
Jose Amador
Jim Allyn - N7JA
Robert Malsbury