Re: Variation in readings of R value
Mike
Is the scale of your reactance graph supposed to be in kohms and not just ohms? I think so because at 3 MHz the impedance of the series L-C would be about -j911 ohms. Correct?
Pete
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Re: Variation in readings of R value
Hi Mike,
Please see message # 23812. This documents one approach.
Alan
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What happens when you try to calibrate it? "Can't get it calibrated" isn't very specific. Does the unit fail to respond correctly at some point in the calibration procedure?
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Re: Variation in readings of R value
Hi Pete, it's an air cored coil with an inductance of around 108uH. I made the measurement with an 18pF COG capacitor in series so the plot is showing the resistance around the resonant frequency of the circuit. However at 15 ohms it's higher than I was expecting.
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Mike
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For HF and higher frequencies, L >> R and C >> G are generally good assumptions. We can then simplify the general expressions for complex characteristic impedance and complex propagation constant to:
Zo = sqrt(L / C) ohms
gamma = j * omega * sqrt(L * C) radians per unit length
Because the power dissipating elements R and G are assumed to be zero, the real part of gamma, the attention constant, is zero. Note that if we increase L, we increase the number of radians of wavelength that occupy each unit of length. We can therefore delay propagation by increasing L and that has been done with coax by using a spiral center conductor.
Voice frequency telephone cables pairs are often inductively loaded by placing load coils at intervals. The most popular scheme in the Bell System was 88 mH every 6000 feet, but there are other schemes. The velocity of propagation is pretty low for such loaded cables, although the reasons for loading are to reduce the attenuation and make it relatively constant below a cutoff frequency.
I don't know anything in particular about the special cables for tunnels. I would assume that the "leaked" energy would show up as an increase in attenuation, but maybe someone here knows more about those lines.
73,
Maynard
W6PAP
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On 6/30/23 20:47, Fran?ois wrote: Thank you very much for your explanations.
1/ We found in old spectrum analyzers for RADAR (1960) delay lines made of a coaxial cable with losses. Our teacher had told us that it allowed to have a lower speed of propagation. I guess we can say that it is a lossy coaxial therefore presenting a complex characteristic impedance (true or false?). If we use a nanaoVNA, what will be the consequences?
2/ More recently I have seen the use of radiating coaxial cable to retransmit radios in the tunnels. This is a cable where the outer conductor is split. This type of cable also has a complex characteristic impedance. Also, what would be the consequence with a nanoVNA?
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Re: Variation in readings of R value
Hi MIke
What component type are you using for the test? Trying to understand why the R is changing myself. I would think the resistance of a fixed series resistor would remain fairly constant if it has low reactance itself. PA3A's article shows an example of measuring the Q of an inductor so it is understandable that he would measure a Q of over 200 and a low resistance for the iron powder Micrometals core. His R stays flat as would be expected. I am not familiar with the 4C65.
Vector network analyzers were not the preferred instrument to us for measuring the Q of a coil. The R is so small with respect to the reactance that small variations of the phase angle and magnitudes of the reflection coefficient would make the Q and the calculated R to vary considerably. The old Q meters remained in favor for many years because they used a parallel tuned circuit method (old Boonton Radio Corp 160 and the HP 4342 for instance). In any case it would be interesting to know what type of inductor you are testing. What is the core?
73, Pete
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Doug, I have seen this demo and observed that the calibration procedure was i.m.o. not properly done.
At marker 3:48 of the video you see that after the CAL button in the menu was pressed next the Calibrate button was pressed without pressing RESET first. From the start of this video you may see that memory c0 was already used.
At marker 4:36 of the video the Isolaton and Thru buttons were selected. They are not needed for a one port calibration.
Now at marker 5:01 of the video something remarkable. After the calibration load was removed a swr of 1.37 was showed in the display. With an open port this value should be infinite (theoretically).
Kees
Op 2-7-2023 om 06:06 schreef Doug:
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Michael. Here is a very good demo re the NanoVNA.
Doug
On 01/07/2023 10:25, Michael wrote:
I have a VNA-H.? I can't get it calibrated. I don't think it is the unit, I
think it's just me. I notice some instructions are for newer units. So what
would you recommend? Best instructions and maybe best video on calibration
of this model?
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Re: Variation in readings of R value
OK if I may answer my own question, I repeated the measurement using the S21 method and got a sensible answer.
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Mike
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Re: Variation in readings of R value
Sorry, heres the graph with numbers!
--
Mike
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Variation in readings of R value
I've been following this article on how to accurately measure the Q of a coil:
I measured a series LC circuit and converted the S11 file to R+jX. When I plotted R against frequency I observed a peak at the resonant frequency. Any idea what is causing this?
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Mike
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Re: Pickup Coil Construction for Inductor Measuremenfs
Ok.
I understand. If you cant remove coil from its surrounding circuit, a GDO is usefull.
"(Why? Because oceans on Titan are likely liquid methane, ethane, etc)," interesting. Good luck with that probe. i follow Spacex to see when people get to the moon again.
Is there a good a GDO or schema somewhere. Mine is from Heathkit from stone age.
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Re: Best Windows Software for Nano VNA-F?
I also have a nanoVNA-F with which I am very satisfied: use f < 300 MHz). Thanks to this forum I was able to update the Firmware. It is not essential but we can thus recover the .sp1 and .sp2 files produced by the box directly.
In reality I use my nanoVNA-F always connected to the nanovna-saver software which extends, with the notion of segment, the use of the box. I do a large part of the calculations from the .sp1 and .sp2 files produced by nanaovna-saver. It is good to set nanaovna-saver to produce a lot of measurement points. 2010 measurements is a bit slow but generally optimum.
Using nanovna-saver is quite easy. Remember to reset the CALIBRATE / RESET box each time before using nanovna-saver. It "normalizes" calibrations and measurements on the same basis.
If you are on Windows 10 or above, the standard version installs without problem. I'm on Seven and you need either a specific version or an old version.
73
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F1AMM
Fran?ois
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Michael. Here is a very good demo re the NanoVNA.
Doug
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On 01/07/2023 10:25, Michael wrote: I have a VNA-H. I can't get it calibrated. I don't think it is the unit, I
think it's just me. I notice some instructions are for newer units. So what
would you recommend? Best instructions and maybe best video on calibration
of this model?
-- */If you forward this email, please delete the forwarding history which also includes my email address. When sending emails, please BCC so as to hide all addresses. Thanks for helping to prevent Scammers and Spammers from mining addresses and spreading viruses./ 73 Doug Kearney, VA3DKA * *Ottawa, ON *
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This email has been checked for viruses by Avast antivirus software.
www.avast.com
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Re: Best Windows Software for Nano VNA-F?
On 7/1/23 1:07 PM, Diogenio via groups.io wrote: Group: I have a Nano-F V. 3.1 but have never controlled it from my computer. I'd like to do that, as I need to generate and save an S1P file for some RF transformer work I'm doing.
Can someone please recommend the best public-domain software to use, something that is not buggy or full of spyware? Again, I want to generate and save an S1P file of a sweep.
I use NanoVNA-Saver (which is in Python, and runs on any platform). Others like NanoVNA-App, which is Windows only. Those two seem to be popular. If you're looking for something minimalist, there's nanovna.py - it's a command line utility that I use if I just want to command the nanovna from a script. #!/usr/bin/env bash time ./nanovna.py --start 50000 --stop 100000000 --points 201 -o testxyz --port 0 time does a sweep from 50kHz to 100 MHz with 201 points and stores the output in a file called testxyz.s1p.
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Best Windows Software for Nano VNA-F?
Group: I have a Nano-F V. 3.1 but have never controlled it from my computer. I'd like to do that, as I need to generate and save an S1P file for some RF transformer work I'm doing.
Can someone please recommend the best public-domain software to use, something that is not buggy or full of spyware? Again, I want to generate and save an S1P file of a sweep.
Many thanks,
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Re: Buggy firmware when compiling with GCC-ARM version 12 - ok with GCC-ARM version 8
I think this related to gcc speed optimisation, TinySA code critical to execute timings and can depend from how compiler optimise code
Most of warnings related to ChibiOS low level code
PS gcc v9.3 provide more compact (and possible little slow) code, more high versions can more faster code, and need fix sweep timings
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Buggy firmware when compiling with GCC-ARM version 12 - ok with GCC-ARM version 8
This happens with tinySA as well with NanoVNA, see my github issues:
and
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On Sat, Jul 1, 2023, 7:25 AM Michael <m005kennedy@...> wrote: I have a VNA-H. I can't get it calibrated. I don't think it is the unit, I
think it's just me. I notice some instructions are for newer units. So what
would you recommend? Best instructions and maybe best video on calibration
of this model?
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Re: Connecting NanoVNA, antenna, and manual tuner
In its simplest form you will need an sma to uhf adapter that will connect your nanvna to the tuner in place of your transmitter.
Watch the smith chart along with the swr and or logmag curves while you tune to the frequency you want to work.
As Lester said, its very educational and you just tuned up without transmitting.
I can send you a pic if you need it. Hope this helps.
Bryan, n0luf
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I have a VNA-H. I can't get it calibrated. I don't think it is the unit, I
think it's just me. I notice some instructions are for newer units. So what
would you recommend? Best instructions and maybe best video on calibration
of this model?
|
Jim Allyn - N7JA
Ho-Ro