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Re: VNA and antenna matching : calculating reactance needed to match
Thank you for all the superb replies.
I'm looking for a source that either has the relevant formulas or, where I can figure out the formulas. Ultimately to implement them in some form of auto tuner. (An intelligent version of an autotuner matching algorithm - if that makes any sense). I'm investigating: GNU Octave code and TLW (i have a version of the ARRL Antenna Book). I've used SimSmith, it's a great programme. (Effectively, I'm looking for the underlying math to automate the match.) Kind regards, Andrew |
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Re: NanoVna H4 Showing blank Screen after updating to latest 1.2.20 firmware
On Fri, Aug 25, 2023 at 12:18 AM, Dragan Milivojevic wrote:
Yes I think that's the problem because I did exactly that with my H4 and got the same result. I flashed it again with the correct variant and it recovered. It's easy to miss the "4" when selecting the file to download. -- Mike |
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Re: Front end overload
These nanoVNAs have a smaller dynamic range than the (much more
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expensive) professional VNAs. With a 40 dB attenuator, the signal from the VNA is attenuated by 40 dB on its way from the analyzer to the DUT (or calibration standards), and any reflected signal is again attenuated by 40 dB on its way back to the analyzer. When measuring a short or open (~100% reflection) the analyzer sees a signal 80 dB weaker than the outgoing signal. When the Load cal standard is measured, the received signal will be even lower. The nanoVNA H4 has a dynamic range of 70 dB (at lower frequencies). Thus, during calibration, it is measuring its noise floor. There's nothing there. It doesn't matter what you connect as a calibration standard. All you get is noise. The calibration is quite useless. Even a 30 dB attenuator is going to give you a very poor calibration. 20 dB -- maybe useful. 10 dB -- probably decent. So, you're right, the VNA is not able to "see" beyond the 40 dB attenuator. David On 2023-08-24 20:28, Greg Strickland wrote:
Thank you David. I made a 40 dB Tee attenuator and did the open-short-load-save calibration at the end of the attenuator not |
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Re: Front end overload
Thank you David. I made a 40 dB Tee attenuator and did the open-short-load-save calibration at the end of the attenuator not
connected to CH0. Maybe I did it incorrectly, because Nano VNA appeared to be measuring the shunt resistance of the Tee attenuator, and was not able to "see" beyond that. It appeared device under test side impedance was swamped out by the 3.2 ohm shunt resistor in the Tee attenuator. Will try again tomorrow. |
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Re: Front end overload
Port CH0 ideally presents a 50 ohm resistive impedance to anything
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connected to it. If an attenuator is needed, it should have a Pi or Tee form, so that a 50 ohm resistive impedance is still presented to something connected to it. If a resistor is connected in series with CH0, the impedance seen looking into it and CH0 would be 50 + R, clearly a mismatch to the cal standards. If a Pi or Tee attenuator is used, do the open-short-load-save calibration at the end of the attenuator not connected to CH0. This way the calibbration will "take into account" the presence of the attenuator. David On 2023-08-24 18:35, Greg Strickland wrote:
If I may ask a follow up questionsabout Nano VNA-H. |
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Re: VNA and antenna matching : calculating reactance needed to match
Although the ARRL Handbook states, without qualification, that the shunt element always goes on the high-Z side (2021 Handbook, the latest I have), that is strictly true only when the impedances to be matched are real or for a specific range of complex impedances. For a considerable range of complex impedances, there will be multiple solutions to the matching equations and the network may be reversed if necessary or desirable.
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This is discussed in detail with GNU Octave code to provide solutions in "More Octave for L-Networks," QEX, May/June, 2012. A graph is provided to determine whether an L-network may be reversed to match a particular pair of complex networks. 73, Maynard W6PAP On 8/24/23 15:35, W0LEV wrote:
Also, know that with L-Networks, the shunt element goes on the high-Z side. |
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Re: Front end overload
If I may ask a follow up questionsabout Nano VNA-H.
1. Is port CH0 input a 50 ohm resistor load? 2. If #1 is correct, would proper attenuator implementation for the port be a series resistor, to form a L pad with the internal resistor? 3. If #2 is correct, would the open-short-load-done-save calibration be done with the measurement plane on the source end of the L pad? 4. If #3 is correct, would scale or another adjustment need to be done to account for a pad between Nano VNA and antenna under test. btw- the parallel LC "trap" worked at the antenna tower and it reduced the nearby RF source down to less than 100 millivolts. Moving the measurement plane to "cancel out" the trap did not work for me. I was able to obtain presumably credible results by removing the measured impedance of the trap by itself from the measured impedance of the trap and antenna. What concerns me is DC resistance of the trap inductor in series with an antenna that might be 27 ohms at 55 ohms of capacitive or inductive reactance at the operating frequency. Good news is I have not "blown up" the Nano VNA yet. Thoughts or suggestions are appreciated. Thank you |
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Re: NanoVna H4 Showing blank Screen after updating to latest 1.2.20 firmware
You probably flashed the wrong firmware variant, you used H version
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instead of H4 version. On Thu, 24 Aug 2023 at 21:04, <john.bachofner@...> wrote:
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Re: VNA and antenna matching : calculating reactance needed to match
On Thu, Aug 24, 2023 at 12:46 PM, Andrew (G1RVD G0Z) wrote:
A couple of things to consider: - When you say "measure the impedance of the antenna" in this case you are really measuring the impedance at the end of the coax feedline. It will be much different at the antenna feedpoint. - Make sure that you don't have any current flowing on the outer surface of the shield (the "3rd wire"). This usually requires a balun or RF choke ("isolator"). If you don't do this the measured impedance will change when you connect the USB cable which has a ground shield on it. You can check by measuring the impedance on the NanoVNA with and without the USB cable attached. - There is a LC match feature in recent DiSlord firmware for the NanoVNA - If you have a copy of the ARRL Antenna Book the CD comes with a program called TLW that will design various type of tuners and gives their matching efficiency. - Here is an online LC match calculator: Roger |
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Re: VNA and antenna matching : calculating reactance needed to match
Also, know that with L-Networks, the shunt element goes on the high-Z side.
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Dave - W?LEV On Thu, Aug 24, 2023 at 9:49?PM alan victor <avictor73@...> wrote:
Hi Andrew.-- *Dave - W?LEV* --
Dave - W?LEV |
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Re: VNA and antenna matching : calculating reactance needed to match
Hi Andrew.
You can also apply a formula, use a pencil and paper and a calculator and obtain a simple match that will accomplish most Z matches to an antenna. If you have a representative frequency, S11 and conversion to it's Rs and Xs values, lets take a look and run an example of your case. Also, consider looking at this site, very easy to apply: |
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Re: VNA and antenna matching : calculating reactance needed to match
SimSmith includes various matching topologies as part of the Smith Chart
presentation: Dave - W?LEV On Thu, Aug 24, 2023 at 7:46?PM Andrew (G1RVD G0Z) <andrew@...> wrote: Hello,-- *Dave - W?LEV* -- Dave - W?LEV |
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VNA and antenna matching : calculating reactance needed to match
Hello,
Having read through the Group, I've not been able to find an answer to my question, but I have found a lot of information that suggests several members of the Group will know ... here's the question: Let's say one measures the impedance of an antenna, reading the S11 parameters from the NanoVNA via USB, converting the reflection coefficients to real & imaginary impedances (thank you Rich NE1EE for your spreadsheet). Does anyone have a spreadsheet to calculate the necessary reactance (L C) that needs to be added in a L match tuner (with series L)? Effectively, a spreadsheet, or formula, that replicates what one would normally use a Smith chart to achieve. Thanks in advance. |
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NanoVna H4 Showing blank Screen after updating to latest 1.2.20 firmware
I recently purchased a NanoVna H4 and found that it had the 1.2.14 firmware. I followed the procedure for downloading the DFU uploading application, then downloaded the firmware. I connected the NanoVna to my computer, placed it into DFU mode, and uploaded the firmware through the App (successfully according to the App). I then disconnected the USB and turned off the NanoVna. When I tried to turn it back on, I get a blank screen. It is fully charged and I have tried to repeat the upload in case there was an error. However, I just get a blank screen,
Anyone have any ideas on how to fix this issue? I suppose I could go back to the 1.2.14 firmware if I could find it. I would prefer to be using the latest firmware. Thank you in advance for any assistance. John R. Bachofner KJ7AOL John.bachofner@... |
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Re: some Nano VNA SAVER 40m antenna graphs
Thanks, Jim. As you have likely gathered by now from my (too many) posts,
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in retirement I'm into promoting the hard sciences and math to the HS bunch and helping others learn the finer points of all things RF. Yes, I will contact Dr. Iyer. Thank you so much for the reference! Dave - W?LEV On Thu, Aug 24, 2023 at 4:39?PM Jim Lux <jimlux@...> wrote:
On 8/24/23 8:09 AM, W0LEV wrote:--Excellent work, Barry. I've always contended introduction of theNANOVNAswould be an outstanding tool for learning. You've proved that. TheThe universities *are* buying these by the dozen. *Dave - W?LEV* --
Dave - W?LEV |
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Re: some Nano VNA SAVER 40m antenna graphs
On 8/24/23 8:09 AM, W0LEV wrote:
Excellent work, Barry. I've always contended introduction of the NANOVNAsThe universities *are* buying these by the dozen. Prof Ashwin Iyer at University of Alberta used them in a "intro class" along with a VOM (ECE 478) a bunch of parts and modules, etc. Even a soldering iron. During COVID isolation. They had a great experience. Might be behind a paywall A. K. Iyer, B. P. Smyth, M. Semple and C. Barker, "Going Remote: Teaching Microwave Engineering in the Age of the Global Pandemic and Beyond," in IEEE Microwave Magazine, vol. 22, no. 11, pp. 64-77, Nov. 2021, doi: 10.1109/MMM.2021.3102649. They did a great job. They had multiple resources, TAs who could explain on a one-to-one basis, etc. If you want to pursue more info, Prof Iyer would probably be happy to talk to you. Prof. Ashwin K. Iyer <iyer@...> |
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Re: some Nano VNA SAVER 40m antenna graphs
Excellent work, Barry. I've always contended introduction of the NANOVNAs
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would be an outstanding tool for learning. You've proved that. The universities ought to be buying these in the 100s to teach what you have learned. Dave - W?LEV On Thu, Aug 24, 2023 at 12:37?PM Barry K3EUI <k3euibarry@...> wrote:
What I found reassuring is that the four graphs (on all three antennas)-- *Dave - W?LEV* --
Dave - W?LEV |
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Re: Length Measurement
Donald,
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I'm not sure I can get the resolution necessary from the "far" end. The cable is 100m long and the fault is about 240mm from the "near" end. Geoff On 8/23/2023 4:07 PM, Donald S Brant Jr wrote:
On Wed, Aug 23, 2023 at 04:52 PM, Geoff Peters - AB6BT wrote:So the question is...can I trust that number?Measure from the other end and see if the two results add up to the correct total length. If they do you can at least have better confidence. If they doi not you know there is a problem. |
Roger Need
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