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Re: Question
Hi Dave,
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On this list there are quite a few who are not amateur radio users. I play at HF with my amateur license and very rarely at 144 or 450 MHz. I hardly need a nanoVNA for my casual use of VHF/UHF. A couiple dollars worth of materials and a standard recipe for an antenna gets the YaeComWood radio happy. The higher in frequency we go the fussier the measurements. Metrology can be a "hobby" unto itself but some of us earn(ed) part or all of our livelihood making some serious measurements. Some people use the word "precision" as a synonym for *absolute* but precision comes in degrees and *absolute* is probably non-existent. In some of my work we made measurements to a few millionths of an inch. The cost of the instruments and maintenance of the standards was quite high. More precision costs more money so we use only as much as is needed. We see that "good enough" really is good enough. In any measurement effort the precision of the measuring equipment and standard(s) should be at least a degree of magnitude better than the tolerances expected of the outcome. 73, Bill KU8H bark less - wag more On 8/14/20 5:34 AM, David Wilcox via groups.io wrote:
I may be dumb and old but I have the MyAntennas 4010 antenna and just hooked my nanoVNA H4 up to my shack coax for the readings. Isn¡¯t the result I see on the VNA the same thing my transmitter sees? I welcome more erudite replies. Anyway I am happy with the result. It works, the antenna and the VNA. Looks the same on my YouKits FG-01 analyzer. I welcome correction in my aged thinking. |
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NanoVNA Saver V0.3.7
Hi
I have just downloaded NanoVNA Saver V0.3.7 for Windows 7 64bit and I have a couple of questions. In V0.3.7 it starts up with a very wide Marker area with the analysis button at the bottom which leaves very little space for the graphs. I can resize it but every time it starts it reverts to the same thing. Also I noticed that the markers are all in use and I can't find a way to get rid of them. I do like to use 1 marker but having 5 there at various points is too much. I have tried deleting the frequency for each marker but some other value pops up once I leave that area. Neither of these 'features' were present on V0.3.6. Am I doing something wrong or missing something? Regards, John |
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Re: Question
On 8/13/20 10:29 PM, John Gord via groups.io wrote:
When calibrating at the end of a long cable, especially at higher frequencies, remember that the cable phase influence will change significantly if the temperature changes. Teflon, particularly, has a rapid change in dielectric constant at about 20 C.Here's an article by Times Microwave 1000ppm (0.1%) change over 20 degrees temperature is typical This is a big deal for a long cable in microwave systems, not so much for a 30 meter cable at 30 MHz (half a degree of phase). Another one of those -40dB sorts of moles popping out of holes that need to be whacked if you're doing precision metrology. On Thu, Aug 13, 2020 at 07:09 PM, Jerry Gaffke wrote: |
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Re: Remote Operation of NanoVNA-H
Some people preserved the code, you can find the links in this group:
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/g/open-nanovna/ On Fri, 14 Aug 2020 at 14:30, Larry Rothman <nlroth@...> wrote:
Dave,If you want to be in compliance with the GPL, you cannot publicly |
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Re: Remote Operation of NanoVNA-H
Dave,If you want to be in compliance with the GPL, you cannot publicly share any binaries without the corresponding source code.Since OneofEleven deleted her Github repo - there is no source code publicly available to share anymore.
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Of course, you are free to do as you please, as other have done. ...Larry On Thursday, August 13, 2020, 8:58:04 p.m. EDT, Dave VE3LHO <dave@...> wrote:
Larry I have to ask:? why privately? On Thu, Aug 13, 2020 at 06:05 AM, Larry Rothman wrote:
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Re: Question
I may be dumb and old but I have the MyAntennas 4010 antenna and just hooked my nanoVNA H4 up to my shack coax for the readings. Isn¡¯t the result I see on the VNA the same thing my transmitter sees? I welcome more erudite replies. Anyway I am happy with the result. It works, the antenna and the VNA. Looks the same on my YouKits FG-01 analyzer. I welcome correction in my aged thinking.
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Dave K8WPE David J. Wilcox K8WPE¡¯s iPad On Aug 13, 2020, at 2:10 PM, K2STP Chris <ccarrara@...> wrote: |
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Re: Poor Quality 50 Ohm Load - Where to get accurate ones?
A further thought on accuracy of standards.
I suspect the transmission impedance of most coax cables which claim to be 50 ohm probably has a 2-5% tolerance between reels, and possibly 1% variation along its length of a single reel. You only need to gently tread on the coax to distort it and change the impedance in the piece under your foot, which will cause a slight reflection of power going to your aerial. A moderately sharp bend in the cable will do likewise. There is a reason why professional installations use fairly rigid cable like Heliax. It is far more important that your calibration load presents a constant resistance across the range of frequencies you wish to study. Steve L |
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Re: Poor Quality 50 Ohm Load - Where to get accurate ones?
Surely, as I recall, it is not the accuracy of the dc resistance of the load that is most important, but the ac impedance of the whole device as the frequency increases. Inductance of the resistor(s) in the load, capacitance across them, poor connector dimensions are FAR more important if you want good results above hf frequencies. Construction of these reference loads is critical, which is why the professional ones useable above 6 ghz cost many times the cost of the nano. Making a good short and open is a walk in the park by comparison.
There are several sites on the internet which show how to make your own sma standards which can be quite good up to several ghz. I have made several sets which are almost as good as some cheap ¡°professional¡± ones I have, but I have not managed to get them assessed on a professional vna. Unfortunately, owners and users of really good kit do not like ¡° foreign¡± stuff to come near their gear in case dodgy connectors damage the ones on their ?20,000 plus vna. Likewise they never loan their standard out. Steve L. G7PSZ |
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Re: Poor Quality 50 Ohm Load - Where to get accurate ones?
use 6 @ at 300 ohm smd resistor 1% or
(middle page) (23ghz) hi, Red Owl Il giorno ven 14 ago 2020 alle ore 02:57 Bob Albert via groups.io <bob91343@...> ha scritto:
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Re: Question
Bob Albert
I found it interesting and gratifying when I measured an antenna via lots of RG-213 with my newly acquired R-X meter.? It showed around 51 Ohms at resonance.? I do that routinely with the nano but it was so cool to do it with my antiquated boat anchor.
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Bob On Thursday, August 13, 2020, 10:29:49 PM PDT, John Gord via groups.io <johngord@...> wrote:
When calibrating at the end of a long cable, especially at higher frequencies, remember that the cable phase influence will change significantly if the temperature changes.? Teflon, particularly, has a rapid change in dielectric constant at about 20 C. --John Gord On Thu, Aug 13, 2020 at 07:09 PM, Jerry Gaffke wrote:
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Re: Question
When calibrating at the end of a long cable, especially at higher frequencies, remember that the cable phase influence will change significantly if the temperature changes. Teflon, particularly, has a rapid change in dielectric constant at about 20 C.
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--John Gord On Thu, Aug 13, 2020 at 07:09 PM, Jerry Gaffke wrote:
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Re: Question
Jim wrote:
This is more a problem with microwave frequencies - at 10GHz,Indeed. For most of us operating below 30mhz, calibrating the VNA through 100 feet of RG8X should be just fine. If you have your doubts, then compare it once with VNA reading taken directly from the antenna feed point. It's good to be able to do a damage check from the operating position on a dark and stormy night without breaking your neck. So just calibrate and operate the nanoVNA as you normally would, except you are doing this through 100 feet of RG8X instead of the 1 foot long SMA cables that were provided with the nanoVNA. Jerry, KE7ER |
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Re: Poor Quality 50 Ohm Load - Where to get accurate ones?
On 8/13/20 6:04 PM, AB6BT wrote:
What are you using to measure the load resistance?This is a nice example of the rabbit hole (or prairie dog village) one can go down.. Is the DC resistance the RF resistance? Maybe, maybe not. Generally, though, DC resistance is less than AC resistance. What's the temperature coefficient of a) the load b) the ohmmeter What is the lead resistance on the ohm meter (or was it done with a 4 terminal Kelvin measurement)? First hit on google brings up Klein test leads that are 41" long, but they don't say what gauge the wires are. let's say they're something like AWG 20 - that's 0.01 ohms/ft or about 0.07-0.08 ohms total - although usually, the meter is calibrated to read zero with the leads shorted. Looking up something like a venerable Fluke 113 - the accuracy specification is 0.9% + 2 counts with a resolution of 0.1 ohms 1% of 50 ohms is 49.5-50.5 ohms This is not meant to beat up on Glen, but it points up the challenges in making accurate measurements - you have to worry about "everything" - just because the NanoVNA reads down to -100dB doesn't mean that it's *accurate* at that kind of level. I spent a while about 20 years ago at work trying to accurately measure a 100 dB attenuator to 0.1dB uncertainty - it's an ordeal. Fortunately, most of us are making "relative" measurements - tuning a filter, checking pass band attenuation, looking for a good match on an antenna. The people who worry about getting a 40dB match (1% voltage) are people running a LOT of power (S11 of -30dB from 200kW is 200W reflected) or doing precision calibration of things. Mismatch uncertainty becomes the dominant error source in precision RF power measurement - I built a 13.402 GHz precision noise source for amplitude calibrations, and it had lapped and pinned waveguide flanges, with an mate/remate uncertainty (measured) of, I think, 0.0001 in the reflection coefficient (that's -80dB) - because we knew it's noise temperature was about 8400K, +/- <2.7K (i.e. 0.1%) These two papers (especially the second one, which has more details) describes the kind of painstaking effort it takes to drive uncertainties below 1% And this is where the $100k VNA with the $20k cal kit earns its keep - when the engineering cost on the thing you're measuring is $500k. Ultimately, be happy with your 51 ohm load! At 05:52 PM 8/13/2020, you wrote:The 50 OHM load (SMA-Male) that came with my nanoVNA-H4 measures 51.13+ ohms.? Not a good start for calibration.? Where is a good source for GOOD loads that are accurate? |
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Re: Poor Quality 50 Ohm Load - Where to get accurate ones?
On 8/13/20 5:52 PM, Glen Jenkins WB4KTF wrote:
The 50 OHM load (SMA-Male) that came with my nanoVNA-H4 measures 51.13+ ohms. Not a good start for calibration. Where is a good source for GOOD loads that are accurate?that's a VSWR of 1.023:1 and a S11 of -39dB 55 ohms is 1.1:1 How much are you willing to pay? Pasternack has a SMA Male load (PE6002) for $38 VSWR specified at 1.17:1, which is worse. For $1900 they'll sell you a 3.5mm load for a cal kit up to 4GHz they claim S11 mag <-40dB That's about the same as the load you have. It will come with a certificate, though. They have a cheaper one for $485 PESTR1001 - it's actually better up to 3GHz, -44dB for S11 mag, worst case, typical is -46 The chart in the data sheet actually shows better than -50dB at 1 GHz |
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Re: Poor Quality 50 Ohm Load - Where to get accurate ones?
What are you using to measure the load resistance?
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At 05:52 PM 8/13/2020, you wrote:
The 50 OHM load (SMA-Male) that came with my nanoVNA-H4 measures 51.13+ ohms. Not a good start for calibration. Where is a good source for GOOD loads that are accurate? |
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Re: Remote Operation of NanoVNA-H
Larry I have to ask: why privately?
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On Thu, Aug 13, 2020 at 06:05 AM, Larry Rothman wrote:
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Re: Poor Quality 50 Ohm Load - Where to get accurate ones?
Bob Albert
Loads are widely available.? Check ebay for example.? But why do you need an accurate load?? 51 Ohms represents an SWR of 1.02.? And how are you measuring it?
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On Thursday, August 13, 2020, 05:52:44 PM PDT, Glen Jenkins WB4KTF <wb4ktf@...> wrote:
The 50 OHM load (SMA-Male) that came with my nanoVNA-H4 measures 51.13+ ohms.? Not a good start for calibration.? Where is a good source for GOOD loads that are accurate? -- ----- Glen Jenkins, WB4KTF, Austin, TX |
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Re: H4 lcd availability
Glen K4KV
Gyula,
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Yes, the 40pin fpc cable and the single strip of pins do the same thing I was told. The single strip is easier to "bread board".? I will use the fpc connector eventually when a board is made... 73 Glen k4KV On 8/13/2020 13:19, Gyula Molnar wrote:
Hi Glen, |
David Wilcox K8WPE
Gyula Molnar
Glen Jenkins WB4KTF
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