Oh yes...there is a LOT of "black magic" in R.F.! You are right on that one. In part this is because stray inductance and capacitance is *everywhere* and this stuff throws all sorts of curve balls at us. 🙂

Thank you and you are very welcome. I will be interested in hearing how this project works out. 🙂

Thanks, man! 🙂

It also depends on the limits of the VNA and its ability to "calibrate" outside of the 50 Ohm world. I am sure that with some situations you will have to use the pad as the VNA just cannot "reach that far." You are right, the VNA will "calibrate out" the loss of the pad. Thank you for the encouragement in the video quality. I am always trying to "improve my serve" so to speak. I, too, get frustrated with folks that never seem to get where they say their going. Have a Merry Christmas! 🙂

You are very welcome! 🙂

You are very welcome! 🙂

Thanks! 🙂

The video from that major manufacturer of high end VNAs, etc actually showed the ends of the two N connectors. To begin with, the center pin is a different size. Ya plug the bigger guy into the smaller guy and you damage the smaller guy's receptacle. But, you are right ... lower frequencies are far, far more forgiving! There the stray capacitances and inductances, cable & wire lengths have far less affect on measurement outcomes. I, too, breath a sigh of relief when I can work down there. Thank you for the kind compliments and encouragements. I am always looking for ways to "improve my serve." 🙂

@@electronicsfortheinquisitiveex Right. I guess I didn’t make clear when I was talking about the N-connector geometries; I was actually trying to say ‘electrical-geometries’ and how far up would you have to go in frequency, to actually see the minor mechanical changes they deemed necessary. In my mind, they probably should have made a different connector so that to the uninitiated, they look the different. I, myself have worked with N-connectors (even repairing commercial equipment) and never came across the 75-Ohm version! On another note, you were aware of my comment (from your other video) regarding common-mode measurements of a 1:1 balun. I did look at the reference you sent me, and (in his hand drawn test-schematic) showed yet another way of doing it. So, I think we’re up to about 4 ‘prescribed’ methods that simply cannot all be right! So, I thought I’d put this comment here since (to me) the CMR measurement across the balun would certainly be ‘another world’ impedance. Anyway, in all of those CMR measurement methodologies, they are trying to (with resistors) trying to interface it with VNA’s 50-Ohm system. And this to me defies logic in that a CMR measurement is just that; it is not a differential measurement, which would imply a certain input/output impedance (i.e., you are looking for the amount of parasitic conduction of what might be termed (in coax land) as the I3 common mode current. And these parasitic conduction is being mitigated my the core’s permeability. So, the confusion for me, is the fact that we are looking at common mode, not differential, and therefore, given the individual 1:1 balun’s physical configuration, I don’t know that you could make any assumptions about its inherent common mode impedance; such that you could simply throw a few strategically placed resistors and you’re good! So these are the things, that keep me up at night, and eating way too many cookies! 😂 73…

@SpinStar1956 Gotta watch out for those cookies!!!! LOL ;-D Yeah, making measurements on BALUNs, including CMR is tricky. The REAL method for measuring CMR requires a VNA with more ports than anything I have (I think 3 is the minimum). So, we have to find ways to do this on a poor man's budget. The resistive divider is the answer which I choose. I can do that! In the end, I ask the question, "How accurate do we **really** need to be?" We just have to have a reasonable expectation that we are getting an indication of the real CMR of the balun. Thankfully, we do not need laboratory quality measurements to determine if the BALUN is a bust or not. Not all do a good job of it. 🙂

Yep, the transformer is a very viable solution. It is more frequency dependent that a well built resistive solution, but it is still a very good one! 🙂

@@electronicsfortheinquisitiveex Also, remember the L, PI, and T resistive pads are lossy. Note that the dynamic range of NanoVNA, for example is only 40dB advertised, in reality is no more than 35dB after the connection and the wires. So, if your pad has say 6dB loss, you can not measure say return loss of 29dB or higher.

@@aduedc I think you are mistaken about the specifications of the nanoVNA. Check out this page ... nanorfe.com/nanovna-v2.html#specifications

@@electronicsfortheinquisitiveex yes this is the newer one even this specify S11(return loss) at -40dB. the old one that does not go above 1GHz is even worse.

@@aduedc Aaaah...I guess I was looking at the S21 for measuring the frequency response of a filter or other device. Besides the genuine article nanoVNA's S11 noise floor limitation, there are those cheapo knock off clones that do not perform anywhere near as well. We still come back to the question ... How good is good enough for our application? For many guys just looking to see the performance of an antenna ... these differences may not be significant enough to bother. Besides, for this group, they don't even need impedance conversion; they just need to calibrate their nanoVNA with a 75 Ohm load if they are working with a 75 Ohm system ("mechanical impedance conversion"). I'm not quite sure the limitation of the nanoVNA regarding what you can calibrate it with. Could someone calibrate it with a 450 Ohm load?

As a sanity check, I looked in every antenna book I have to try to verify this answer, but they all talk about impedance relative to length, not height above ground; this even my college textbook on the subject! 😞 Here is my educated guess ... the impedance of an antenna is a complex entity consisting of inductance, capacitance and resistance. This includes it proximity to nearby objects like buildings, other antennas and ground. If we remember that capacitance is any two conductors (e.g. the antenna itself and ground) separated by an insulator (e.g. air) and is inversely proportional to the distance between said conductors (e.g. height of the antenna), then we can also see the capacitance of the antenna to ground increasing with reduced height above ground. Increased capacitance = decreased impedance. Am I right on this one? Dunno, but that's my take on it. No one else is fessing up to the facts. 🙂

@@electronicsfortheinquisitiveex Thanks, that makes sense.

@@AL-kn4yx 🙂

I'm a big one to carry WAY too many decimal points in the middle of my calculations and then round at the end. I've been burned by rounding too early in the process. But you are right, is this measurement close enough for your application?? Let's not stress out over unnecessary precision or too many decimal points.

Yes, they do! Man, they do make fantastic stuff. 😍 As I understand it, these are only switchable between 50 and 75 Ohms. This still leaves the guy who is trying to measure his 450 Ohm antenna grasping for answers. So, while I am using a 75 Ohm environment for this video demonstration, the aim was far more general than this. 🙂

@@electronicsfortheinquisitiveex My RigExpert antenna analyzers can do 25, 50, 75, 100, 150, 200, 300, 450, 600 Ohm system impedance.

@@mikesradiorepair WOW! Now THAT is quite impressive! Those RigExpert analyzers are awesome units! I am wondering, though, are they actually changing the output impedance of the unit or just changing the math (and calibration numbers) inside the device? As you saw in my video, you only really have to change the math for impedance measurements for many applications (SWR, Return Loss, Reflection Coefficient stuff all remains the same). The only place where the actual output impedance makes a difference is when doing the thru measurement. Because it doesn't do through measurements ... just thinking and wondering.

@@electronicsfortheinquisitiveex I believe it is probably done in software. And setting here thinking about it, it would almost have to be. Since it only has one RF connector and it's a 50 Ohm N female. They don't have a different connector for each system impedance.

I think you are right. Gotta LOVE those N connectors. MUCH more expensive than the UHF (SO/PL) connectors, but worth every penny.

And I will bet good money that all of this cost a LOT of $$$$$. I looked at Pasternack, primarily. Also DigiKey, Mouser, Newark and a couple of other R.F. places. I do not remember finding anything. If I *did* find one, the price was probably WAY more than I cared to pay (admittedly, I am quite "frugal"). 🙂