Закрито GRAVITATION BOOK & General Relativity 2
I have the *Gravitation* book by Misner, Thorne, and Wheeler (publisher: Princeton University Press, ISBN: 978-0-691-17779-3) . Even the first chapter without math gives a good rendition of what's in store with Einsten's General Theory. Yes, it's a difficult read for all the higher math, but well worth it. I seriously doubt I'll finish it in "digested manner" by the time I push up daisies. In the first chapter on page 5 I especially like the quote: "Space acts on matter, telling it how to move. In turn, matter reacts back on space, telling it how to curve." He uses an ant attempting to navigate the surface of an apple as an example of the ultimate outcome of General Relativity with the stem as matter and the surface of the apple as the curved (but straight) geodesic. It's a masterful analogy but will bend one's mind even without all the math. WARNING: If one decides to purchase this wonderful mind-bending book and expects to "digest" it, one better right off the bat on opening the cover get used to a 4- dimensioned coordinate system used ONLY to locate and describe an event. Further, coordinates generally do not measure distance in curved space/time. Nor are events described by some far off "reference plane". Thought you knew plane and solid geometry. Better think twice...... FURTHER WARNING: It rapidly becomes far deeper than that. Dave - WØLEV -- Dave - WØLEV
Розпочато W0LEV @ · Останніх @
SWR vs. Resonance 145
Hey there knowladge base people, I’m H4 user. I’ve been tuning some EFHW`s and checking various UHF/VHF aerials for handhelds for a while now. HF’ I’ve build 49:1 un un 20m wire for 7,14,21,28 mhz frequencies. Usually display set 6-29Mhz and calibrate VNA. During the tuning proces I usually make the wire little longer and than shorten it by 15-20cm and than watch the SWR and resonance on freq. I intend to use. Here is the question: Why does the resonant frequency and SWR are not same? From previous discussions here, I’ve gained awareness that all measurements are more accurate when choosing smaller Span between the stimulus say insted 6-29mhz choosing 6-8mhz (40m band) - 20-22mhz for (15m band). I’ve tried to measure smaller section with similar results those being: when Recall from calibrated memory say 6-8mhz for tuning on morse portion of 7mhz band, the SWR will be say 7.030 yet the resonance displayed on thel left will be @ 6.870 Why is this happening ? Am I missing some technical or physical understanding ? J. OK4SU 73
Розпочато Jakub Sutorý @ · Останніх @
SV4401A review 20
I recently purchased an SV4401A from Aliexpress for $299. As a lab instrument, it is very nice, a giant step up from the F-V2. With up to 1001 data points, the sweep resolution is great. The N connectors are nice too, though a cal set of N types would have topped it off. It has mass and is ruggedly built, inside and out. The batteries are replaceable without soldering. My unit has two serious issues, which I am trying to work through with the tech guy at Sysjojnt, who also developed the V2. The software nanovna-saver is picky about which Win10 pcs it'll run on. I get a failed to execute script msg. Strangely it runs on my cheap tablet and a desktop at work. Three others will not work. I am not a pc or Windows expert. Maybe there is a setting that will let it run? The other issue I have is that, when left off for a while unplugged, it will not boot. Instead, it cycles through a power on sequence indefinitely. The batteries are fully charged. So to take it outside I must bring a 5VDC power source with type C USB connector. Whether these problems are design flaws or just with my unit remains to be seen.
Розпочато Ken Bozarth @ · Останніх @
NanoVNA <---> TinySA ultra 18
Anyone tried to connect their NanoVNA directly to their TinySA... Very interesting. See pics below. The VNA is set to sweep from 125MHz to 175MHz. The SA is wide open from 0 to 800MHz. I was surprised to see signals all over the band though most are concentrated in the sweep limits. Notice LOGMAG is flat and the Smith chart shows no change across any range.. NOTE: There is 30dB external attenuation between these two... Just to be safe. Pic 1 AVG 4 Pic 2 MAX HOLD Pic 3 random shot no calc on trace
Розпочато Matthew Rapaport @ · Останніх @
parasitic capacitance tests 9
Hello everyone. A colleague told me that it is possible to perform certain transistor tests with a VNA, but he doesn't know where he saw such a practice. Is it really possible to perform such parasitic capacitance tests, and how would it be done? Could you point me to a tutorial on the subject? Thank you. -- Carlos Delfino Equipe Basicão da Eletrônica <https://basicaodaeletronica.com.br> Celular: (85) 985-205-490 (OI) - Aquiraz/CE <https://basicaodaeletronica.com.br>
Розпочато Carlos Delfino @ · Останніх @
Antenna Propagation video - old but with very good commenters #tutorials
Further to the SWR vs Resonance thread, I have started a new thread here. Have a look at https://youtu.be/-F7KYLO4Bkg?si=v6utQyiV5rKRwYPi There are some excellent comments posted as well. Should we move this thread to the Ham Antenna forum? -- Bernie Murphy, VE3FWF *Real* radios glow in the dar
Розпочато Ham Radio @
Testing a rubber duck 11
Just for fun, I tried connecting the rubber flex antenna from my Yaesu FT-70D handheld directly to the SMA connector on my NanoVNA (after calibration) and seeing what the characteristics were. I was pleasantly surprised on 2m. I figured that holding the VNA as shown would pretty closely simulate the same effect as holding the HT, and that seems to be the case. The resonant frequency did vary with the position of my hand, but it stayed pretty well within the 2m band. In the photo, the marker is at 146.0 MHz, SWR is less than 1.167 at minimum, impedance is approximately 55 ohms. On 70 cm, though, I found it to be much less cooperative. at 445.2MHz, SWR was about 2.8:1. Impedance reads 51.6 ohms net, but very capacitive (32.7 -j39.9 ohms) I'm not sure here whether being mounted to the HT would make a difference, and it is difficult to measure with any sense of accuracy.
Розпочато Neil Preston W0NRP @ · Останніх @
Setting Stop Frequency to 1500 MHz on NanoVNA-H 3.4 10 #nanovna-h #edy555_nanovna
I recently bought the NanoVNA-H ver 3.4 and I have upgraded the firmware to the following release (https://github.com/hugen79/NanoVNA-H/releases/tag/0.4.5-4) to allow it to measure beyond 900 MHz. After installing this release however, I am still only able to measure up to 900 MHz. Is there a different release I need to be using to enable a 1500MHz stop frequency?
Розпочато river@... @ · Останніх @
White Screen, Can't reset (is it broken for good?) 4
I need some advice... My Nano-VNA-H (Ver. 3.4) has operated well since I got it in 2020, and I've never had any problem either updating the f/w (the latest version in it is 1.2.20) or connecting to my laptop to operate Nano-VNA-Saver, although I haven't used it much lately (as one could tell from the f/w version). I tried to connect it to my laptop the other day (Dell Inspiron with Win 11) to run Saver, but it wouldn't connect. I kinda figured that maybe the firmware needed updating, especially when I found out that the most recent DiSlord version was 1.2.40, so I d/l'ed NanoVNA-H.v1.2.40.dfu and went to "https://www.st.com/en/development-tools/stsw-stm32080.html?s_searchtype=keyword", looking for STSW-STM32080 (DfuSe USB device firmware upgrade). But there was a notice there that said: "This product is NRND We recommend you that replacement part: STM32CubeProg". So I went and d/l'ed that. After trying to update the f/w with that, all of a sudden I have a bricked white-screen non-functional paperweight. But under the Win 11 "Device Manager" I do see, under "Universal Serial Bus Devices", "STM32 Bootloader". I tried the "fix a white screen" procedure, shorted Boot0 and VDD on power up, but I've got a broken paperweight. Should I just bite the bullet and buy a new 4" Nano-VNA-H or can anyone suggest a fix. Please understand I'm almost illiterate regarding this stuff, and just got it for basic ham use. Thanks. Barry Leonard KN4JRF exusaf@...
Розпочато jb leonard @ · Останніх @
VNA bricked. 16
Is there any way of getting the VNA back to normal? I tried an update and the VNA just went white screen. It was a H version so decided to do an update to keep it fresh. All it does now is show a white screen and that is it. So is there any way of installing software maybe via SD card as it has a slot or via PC? Any help will be grateful. Will 2M0WHN
Розпочато william Northcote @ · Останніх @
NanoVNA top lines documentation? 12
Is there a link to anything (PDF, YouTube, etc) that covers what the top lines on the NanoVNA can report and how to interpret them (I have the H4)? I know there's a lot that can go on up there... I've searched the forum but not found any comprehensive reference.. thanks...
Розпочато Matthew Rapaport @ · Останніх @
SAA2-N device driver on Win 7 2
When I plug unit in, device manager says it's a CDC-ACM Demo device. Does not appear under Ports (COM &LPT) What is the problem? Works ok under win 10 as a usb extensible host controller and QT software recognize it as port COM 5
Розпочато F4WCV @ · Останніх @
Effect of asphalt under a 10m 1/2w center fed dipole at 1/2 wave elevation 42
A new Technician Class Operator has limitations on putting a 10m antenna anyplace but as a dipole over a paved surface. I do not have any practical experience there and googled around and found nothing specific to this. I'm ready to say no real problem but would like other opinions. I only found on-line that a lossy earth on lower bands has a negative effect. The op does not have a tuner at the moment and by practical application a 10m center fed at .5wl should provide approx 72ohm and 1.4:1 SWR. The radiation pattern appears to be exclusively lobes at a 30degree elevation. Would the asphalt have a great impact here? Anyone? 73, Andy
Розпочато Andrew Harman @ · Останніх @
SV4401A ISSUE 5
I was going to run some comparisons between my Siglent SVA1032X and the SV4401A. I had not used the 4401 in several months. I did an SOLT calibration after setting the frequency range for the test. I thought it odd that all (4) boxes in the CAL page were already checked, but I went ahead and did the full calibration. Clicked on DONE when it completed. I used my HP calibration set and later another valid SOL set. The top of the screen confirms that SOLT is valid, but SWR measures infiniti with any 50 Ohm load and with the through cable attached loss says nan dB. Previously saved calibrations still work. It has been a while, but am I missing something in my CAL procedure or?? Tnx, Dale W4OP
Розпочато Dale Parfitt @ · Останніх @
Checking a Cable with LogMAG and TDA 2
Normally I just compare the results of a cable in question to a known good and determine if the values are too far out of spec. But surely there are faster ways to do that? I have been checking the videos online to look to see about diagnosing a cable. I am aware there is the use of the LogMAG set up to identify a break, as well as the use of the TDR. I think these two technically compliment, though the LogMAG way is only option for older hardware. I have a NanoVNA-F v2 and it has TDR. Though the device says the a 20ft cable is 39 Meters, which makes no sense. So I must be doing something different from the videos. I have a NanoVNA-H4, and it has a TDR function but it's marked as Cable S11, not TDR. So far unlike the F V2 which gives an estimate of length, the H4 gives a cable loss. I see there is a function to add a cable length value and this generates a % which is a multiple of the expected value relative to what was measured. After re enabling everything I was able to get it to read a singular length, though its reading 88.3 meters with and without the cable. Both devices I have tried set up the LogMAG method. Never have I been able to get it to match the online demonstration. Either the cables I am testing are that bad or I have over looked something. The video, he disabled all but S11 logmag on screen, though it Said CH1 LogMag. I am not sure what version of firmware he has, my H4 says M1-M4 if multiple markers are active and S11 if it is a Trace. He seemed to be running 50kh to 5Mhz, and M12 is set to 5Mhz. He did a generic tuning, Open, Short, Dummy, and Thru. However his thru was separate from the other calibrations. I did as he did but though per the DG8 that to calibrate a lead, the Dummy, Short and Open had to be on the ends of the the leads in order to have them cancel out. Like solving a quadratic Equation. So in the end I have not been able to get the F v2 or the H4 to behave the same or to get them to read the same values as the video. So the question is should I try to get the LogMAG method working, or focus on the TDR functions? Per a previous topic question I am generating a couple charts that compare the hardware and firmware options. Work in Progress.
Розпочато Ray Lulling @ · Останніх @
Fun with calibration 8
What happens when you compare different calibration stubs—the 50 ohm load. The NanoVNA comes with 1 50 ohm calibration stub, but you need 2 (and 2 F-F barrel connectors if using the supplied cables) to do a proper ISOLATION calibration for S21 type tests. So I bought for about $15 another stub kit with an identical looking 50 ohm load and F-F barrel connector (a bonus was an M-M barrel connector the original kit didn’t have). Then, also for about $15 I saw a pair of different looking 50 ohm load stubs. I bought those too, wondering what would happen if I compared 50 ohm stubs? What if I CALIBRATED with one type of load stub and then TESTED (S11) the other? The three pics below tell the story. The two stub types match (50ohm, no reactance) only at the low end of my test frequency (1MHz–800MHz) range. They progressively diverge as frequency goes up, and as might be expected, the divergence is inverted. (A) becomes capacitative, and resistance goes down compared to (B), while (B) becomes inductive, and resistance goes up compared to (A)! Is there a difference in real measurements? I tested a J pole antenna across my calibrated range (1-800 MHz). Between 750-800 MHz the frequencies reported for the lowest SWRs varied by 4+ MHz depending on which calibration was used. At 100-150 MHz the measured difference was only 50 kHz. The device can only be as good as its calibration. Professional calibration kits cost THOUSANDS of dollars—I looked. Regarding absolute measurements the NanoVNA using the supplied or other inexpensive calibration stubs is “very close” at lower frequencies and progressively less reliable as the frequency goes up. Users who are doing measurements in the upper parts of the NanoVNA’s frequency range must keep this in mind. —---------- Picture 1: Load stubs (A/Top) supplied with the NanoVNA. (B/Bottom) a second set of 50 ohm loads purchased (cheap) from Amazon. Picture 2. 1MHz - 800MHz calibrate using the (B) stub from picture 1 but testing the (A) stub. Trace 1 is Resistance. Trace 2 the Smith chart. The A (DUT) stub is more capacitative and resistance goes down with increasing frequency. Picture 3. 1MHz - 800MHz calibrate using the (A) stub from picture 1 but testing the (B) stub. Trace 1 is Resistance. Trace 2 the Smith chart. The B (DUT) stub is more inductive, and resistance increases with increasing frequency.
Розпочато Matthew Rapaport @ · Останніх @
NanoVNA non responsive after failed real time clock modification attempt 25
I saw in a previous post that it was possible to modify the device to have a real time clock by adding a 32 KHz crystal which I tried to do. I ended up bridging some pins luckily with the battery disconnected but after I attempted to attach the crystal to the correct pins, connected the battery and flipped the power switch it starts up and looks ok but no sweeping and no response from touching the display. This modification appears to be very high risk and not too much of a reward other than the device knowing what the date and time is along with time stamping files correctly.
Розпочато Nicholas @ · Останніх @
NanoVNA-App DFU 4
Hello all. I have been able to connect NanoVNA-App to my H4 via com 6 just fine. But when I place my NanoVNA-H4 in DFU mode, Com 6 goes away and NanoVNA-App says there is no DFU device connected. What am I missing here? Thank you!
Розпочато avionicsfun@... @ · Останніх @
Best Way to measure an Inductor. 25
Ok I have a NanoVNA-H4 I have three coils I want to measure their inductance. I tried what I saw a few you tube videos of where, I simply calibrate it and put the coil across. well yeah it works maybe. Two of the coils of known value both I tested at 3 to 4 Mhz freq wise. The small one was supposed to be 8.5uh but measures as only 3.7 the bigger one i supposd to be 200uh but measures at 170uh. Now BOTH of them on the smith trace onlu make very small segment of a circle up in the capacitor land like around 1 and 2 o clock. Looking for suggestions. Joe
Розпочато Joe WB9SBD @ · Останніх @
COM Port wird nicht erkannt / COM port is not recognized N1MM+ #nanovna-h #nanovna-h4 #usb
Hallo, ich habe das Problem das mein NanoVNA als USB Gerät erkannt wird und ich habe kein zugewiesenen COM Port. Somit kann ich mit der App auch nicht drauf zugreifen. Welchen Treiber muss ich für Windows 10 Installieren ?
Розпочато DN9CYL@... @
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