U.FL plugs and sockets. A very useful board. I just finished giving an into lecture to NanoVNAs using this board. Went very well. I had read all the negative comments about U.FL, and was concerned about how all that would go. I didn't want to be in the middle of the demo, and have a cable fail. I used a loupe to look at the U.FL plug and socket. I noted that the /sides/ of the /plug/ are /open/ on the coax end, and there is a part of the clasp that rounds the /end/ of the /plug/. Also, the internal part of the U.FL /plug/ that grips the socket pin is designed to rotate in line with the coax axis, /not/ side to side. So I developed the habit of attaching the U.FL by "hanging" the end of the plug on the lip of the socket, then rotating the plug down toward the board in line with the coax axis. To get it to snap into the socket, I'd apply gentle pressure right at the plug as I was rotating downward. Removing is the opposite. I'd guide it off with my fingernails as I lifted the coax end of the plug. I was concerned at first about them being "loose", until I learned that "looseness" is part of the design. I have used the same pair of SMA-U.FL extensions ~100 times, and there is no degradation of the connector, at least at this level of use. I don't get signal glitches, static, broken contacts, or changes in signal quality with the NanoVNAs.
Just as a note: when changing the span/center frequency, the VNA should be recalibrated. I found this out first the hard way, and, afterwards, from a video from w2aew.
The 10.7 MHz BP filter was bad on mine, so I put a good Murata one on. Yes , you are correct, calibration must be done at the end of the cable. Even if you use different cables. I bought some SMA to APX adapters from Megiq.
2:37 - one side of an unterminated attenuator is NOT equal to the characteristic impedance, and cannot be used as a load without some error from the impedance mismatch. It might be acceptable when performing low-precision measurements, but I'd try and have two loads instead.
I hate those darn UFL connectors, they're really not intended for repetitive mating. If it wasn't so expensive I'd build mine into a box with the connectors going to a panel with SMAs. Having said that it is a pretty neat demo.
Pretty sure u.fl connectors are only rated for 20 or 30 matings - they're not resilient connectors - really meant for wifi antennas to be plugged into a wifi card once during manufacturing and never touched again.
the BPF is a SAW filter (perhaps made by Murata?) they are usually never matched to 50 ohm so the circuit is not right for their measurement. Some of them are 150-300 ohm and some have 2-3Kohm I/O impedance. When you measure it in a 50 ohm system the response shows up very crappy unless a proper matching circuit is built around it
There is a 50ohm match on the input. two resistors. looks like an inductor across the filter too. also a series resistor on the output but they loaded it with 0 ohms
Hello sir, I have now found this video of you. i learned from you not to buy this kit and learn it from your video. Bringing out the smith map on the VNA and on a correct scale I didn't know how to do that. . DBs is also something that I need to take a closer look at / to learn Thank you again for a VERY educational video! Healthy and Friendly Greetings from NL / Rotterdam! Rob
those are MMCX connectors widely used in all RF test gear. Prying it up with screw driver was a bad idea as it puts uneven pressure on the socket and the plug. I'd just grab them on both sides and pull them up by pushing my two finger tips to the board.
@@robust5615 Actually that was my point in another comment! Problem is they're really pricey and too much trouble to homebrew...outfitting all the ports would cost as much as about two NanoVNAs! ;-)
So I have a costly R&S VNA here and need to calibrate at the end of a pigtail connector with the small socket just like this one. Do you think its a good idea to use these Demo Boards for calibrating it at 2.4 GHz ? If no, what do you recommend ? Nice video btw.
no, this is a bad cal reference. if you have no money you can do what I did: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-fVzT23onCxI.html not sure how good is is at 2.4G have not measured it. the open and short will probably be OK and I might buy a better load. You can get good priced loads will get you to 18G
As always a great demo. I'll be getting one as a teaching aid. If Google didn't insert mid roll ads it would be a bit easier to follow your train of thought. If Google could at least let you finish the sentence before breaking for an add that would be great.
I tried to set my profile not to place mid roll ads but I guess it didn't stick. If you are teaching you will be interested in a future video in about a month. I have layed out a SMA connector version of the demo board. I will unsolder the parts and move them to my board.
I find this all very difficult to follow for a first timer. When doing short open load, am i supposed to ge through the menu and calebrate each one or does the RF Demo Kit do that automatically. This video seems very vague to me. i think i need a personal tutor.
don't feel bad. vector network analyzers are probably the most difficult piece of test equipment. I have a playlist for 'nanovna' that has lots of videos that may help you.
A BIT CONFUSED On the #1 LP-30MHz (about 7 min into video), I am confused about the high rolloff of this 3rd Order Pi Filter. It would appear to be down way more than it should - like 21db/Octave (60MHz) and 16db/Octave (50 MHz depending on where fc is actually at). I would expect to see something like -10db ish at one Octave. My nanoVNA gives almost exactly the same readings on the same board as far as I can tell. So have the Chinese made a 3rd order filter miraculously act like 5th order filter or am I missing something?? I could be missing something, I am no expert on these things - thats why I am watching videos like these LOL.
from wiki: The frequency response of the Butterworth filter is maximally flat (i.e., has no ripples) in the passband and rolls off towards zero in the stopband.[2] When viewed on a logarithmic Bode plot, the response slopes off linearly towards negative infinity. A first-order filter's response rolls off at −6 dB per octave (−20 dB per decade) (all first-order lowpass filters have the same normalized frequency response). A second-order filter decreases at −12 dB per octave, a third-order at −18 dB and so on.
@@IMSAIGuy That makes sense, my bad. Thanks for the reply. I was hung up on the 3db thing. Its a shame these things have similarities to the db formula for db for voltage/current. For years I assumed they were talking about voltage in the filter section despite reading many ac/dc books from cover to cover (from Boylestad and other authors) - some more than once. Assumption is the mother of all screwups LOL.
Hi IMSAI Guy, congratulations on your excellent videos! Do you have any idea what the metal dots on the backside of the RF demo boards are for? Is that used for a sensor or probe?
they are just various locations on the smith chart (for teaching I guess). open inf + 0j short 0 + 0j load 50 + 0j and two extra points 50 + 50j and 50 - 50j
this board is limited by the stupid connectors, I can never get accurate readings unless I'm pressing them down onto the board (yes they are properly snapped on) I've seen an SMA version.. shopping for one now, who needs stuff that requires fiddling?
