#325 

I've been in electronics communications for over 50 years, and this was never explained. Likely for technicians, unnecessary. However, with the advent of affordable devices like the Nano-everything, this becomes a tool for understanding by playing with it on the bench and ultimately the field. Thank you so much.

I remember a video of a guy (using shf) demonstrating how antennas worked using very tiny antennas. It was pretty amazing. He had verticals, dipoles, beams, loops and so on.

That was pure gold Allan. I think the nanovna is the best bang for buck gadget any amateur can own.

SWR and antenna efficiency are two different metrics. Walt Maxwell was trying to dispell the SWR myths, but people wouldn't listen. A brilliant engineer was designing antennas for the U.S space program might know a thing or two. You'd think...This video is one of the few on youtube that teaches true science

Great! And a great teacher !!! Number one on my list of tips for my pupils

Thanks for another excellent video. I wish all my teachers were as clear and concise as you.

Amazing little device for less than $100. It comes with little useful documentation. Your videos are invaluable. I have learned most of what I know about this thing from your presentations. I drop everything when you post a video. Great Job Again!

Now I realize why my friends dad used to have coax patch cables hanging on the wall that were all six inch different from each other. They started at half a foot and went up to ii think 6 feet. Thanks. Jpol.

This is the visual method of proving that if you have 50oms antena and 50oms trx you can actually cut feeder to any length you want because impedance being in center of chart cannot rotate like you showed. Thank you ✌️

Thank you sir, your videos are very helpful and very practical, and i really appreciate you are using test equipment that we can afford...this makes your videos beneficial to the rest of us.

What a timely video! I've just received my new NanoVNA-F and am getting ready for some practical antennae measurements in the field and also learning and experimenting! Thanks! HNY! 73 Linas LY2H

Thank you Alan, for the video. I love the way you explain things in your video, it makes it very easy to understand complex topics.

Hi Alan, HNY. Another very easy to understand explanation. I learn a little more with each of your videos. Keep them coming. Stay safe. 73 WJ3U

Wow. I would like to understand this more. Maybe I need a NanoVNA.

Very cool!! I can see I have a lot to learn yet. I got a NanoVNA and got SWR curves for a couple of FRS antennae so far...

Fanastic video. Cleared up a lot for me.

Considering the price of these NanoVNA, it looks like, working fine and has fast response

Thanks, Alan. Happy New Year to you and your family. -Vince

Yay, W2AE video.

Thanks Alan.

Thank you for sharing! I am learning something new 👍

👍Thank you sir.

Hi Alan, great video. It would be nice to see some 2.4Ghz antenna matching network..how to do the matching with a VNA..Regards Frank

thank you a lot, your videos are amazing as always, really high quality content yet simple explanation and demo

Thanks Allen for these great videos

Excellent as always ! Thx

Despite of Alan's explanation by means of the Smith Chart, it still might remain a bit hard to understand from a physical point of view why the impedance transform by the cable won't affect the SWR. One could think that any transformed antenna impedance back to the generator would cause an impedance mismatch there against its 50 Ohm output causing further reflections with impact on the SWR. I assume that this is not the case because there's no *physical* impedance mismatch between the generator's output and the cable. The transformed impedance just describes the voltage/current ratio at this point.

Great explanation

Alan, great video as usual. In some future video on the subject, can you show what happens when you add transmission line of a different impedance than the system? As those used in some antennas to correct the impedance. Also, what happens when you add lossy line (SWR goes down, but why). Thanks for your videos and Happy New Year!

Thanks, excellent as usual!

So is this why adding an extra length of coax to your antenna feed will sometimes allow an ATU to match a previously unmatchable antenna system?

You are a very smart dude!

Fantastic, I love watching your videos as I always learn something as you explain so well... I'm getting to grips with the Nano VNA thanks to you. I've ordered the Nano SA and I wonder if you've seen one or had a chance to play with one?

@w2aew - I have enjoyed your nanoVNA videos, thank you. I purchased a Rocket Book after seeing it in action; could you please let me know what ink cartridge holder you are using? Looks interesting.

Interesting.

I got the NanoVNA SAA-2N. In order to read and display SWR, there is a circuit called the SWR bridge. Now, have you tried reading from any tuner? For example, REF and FWD is needed and provided by the SWR bridge, by reading from the tuner coupler where to me the bridge is at. The idea is to tune live, with no carrier on the air, as the analyzer shoots an exciter to the antenna to plot on the display. Now, when both, the tuner and analyzer is used as per above, then both tools become even a better solution, due to tuning live, no carrier, then transmitter is ready to go out on the selected and tuned frequency, rather than analyzing to see where the antenna is resonant at.

Great video, thanks :-) I assume you're adding line of the same impedance as the line already used in the antenna system. Or does this apply as well, if the 'extra added line' is the actual antenna feed as a whole? How does it look in the Smith Chart if you add extra line of another impedance, fx. 75 ohms in a 50 ohm system or vice versa? 73s

Happy new year

Fantastic thanks! How can we make sure (i.e., measure somehow) that the coax does not become part of the antenna?

at 1:56, you show point A as Low Freq and point C as Hi Frequency. I think these are backwards. the point will spiral clockwise as frequency is increased. IE, if this were 40M antenna, point C would be 28 Mhz and point A would be 30 Mhz for instance.

Happy New Year 2021! May the sunspot gods dwell upon us with good DX, a reduction or end to Covid 19, and a plethora of swap meets and hamfests!

Great presentation. If you take request. Please, do a lecture on the minimum noise figure cycles, which is different from matched impedance and its effect on filters and antennas. Here is a reference in this area: Microwave Engineering by David M. Pozar

If you didn't already have a perfectly tuned antenna would the SWR have changed? Do you tune your antenna with calculated half wave lengths? Thanks! The reason I ask is because I tuned a buddy's Big Rig antenna the other day with my Nano VNA H4 with a 6ft RG8X coax to a very low SWR 1.3:1 at 27.205 ctr of the band and ch1 and ch 40 1.5 SWR. Then we hooked the radio back up to his 18 ft RG8X coax and tested with an Astatic SWR meter and ch 40 was like 3.5:1 and way in the red. So we had to cut another 1.25 inches off the antenna to make it work with the 18ft cable. Checking again with the Nano on the 18ft coax every thing looked fine. We cut around 5 inches off that Wilson Trucker 3500 antenna to get the SWR right.

👍

Have you got a source for Smith Charts. I can’t seem to buy any sharp ones. I used to be able to get extra large ones when in Engineering School (a long time ago!)

I have an 80m dipole that’s less than 20’ feet at the feed point. It’s resonant, and works really well, but I’m not sure of the feed point resistance. I’m guessing that it’s probably below 50ohms. I’ve thought about building a balun to match the feed point. Would adjusting the coax length (providing that method would get me closer to 50ohms) be more or less efficient, as far as getting more energy to the antenna. I am exclusively QRP, so every bit helps. Thx and 73’s from VE land.

Very nice video! Congrats. Just one doubt: when I measure the SWR, if I hold it in my hands, the SWR is too much lower than untouched. What is the right way to use it?

Alan: Would it be accurate to substitute "return loss" in place of "SWR" in the context of this discussion?

I don't agree that SWR not change, it could get better since transimssion line add losses, which attenuate returning wave. Of course it is more signifant at higher frequency and longer lines.

Question: For measuring swr and return loss, what is better? Return Loss Bridge on a Service Monitor or Scattering Parameters from a VNA? Pros / Cons to each?

I have a digital HF power/SWR meter, and its power and SWR reading change depending on how long the coax is between the radio and the meter sampling unit (this is with a dummy load for an antenna). For a 100W transmitter, I can make it read 80W, 100W or 130W by changing the coax length by a few feet. We're talking less than 15 feet of coax total. Why is this? I thought the meter was bad, but I have two of them by different manufacturers that do the same thing. If I put a Bird meter in place of the digital meter sampling unit, it always reads a steady 100W forward, 0W reverse, as it should. The length of the coax between the sampling unit and the dummy load makes no difference. I can't figure it out. Its driving me nuts.

So on a mag mount antenna is the coax part of the antenna?

Very interesting! Is it the same effect on UHF frequencies?

I find it interesting you can tune an antenna by using the length of coax. In the RC world, many common 2.4GHz receivers use maybe 5 inches of thin coax with the center conductor exposed usually but not always 31.25mm, FrSky go with an unusually short 28mm or so. Are should these antenna be classified as monopoles or dipoles? is it possible to know what the optimal length is for a mystery receiver with only u.fl inputs?

8:10 yep... 1k like, 0 dislike ! feb 2021 !

So is it better for your desired frequency to be on a resonant point or the lowest swr ?

I saw Smith Charts in various RSGB Handbooks but could never understand where the figures came from, now with my VNA I can see what is going on. Adjusting aerials is so easy now, too short? Too long? I can see now. This is why the C.B. world is obsessed with the ½λ of coax myth. It's because they have no confidence their aerials are tuned properly so tune the coax after hearing about the same impedance. Why not ½λ to the SWR meter as well? What about 4" for the SWR meter but is it on the aerial side or the tx side? That's how daft it is. I've been challenged by a C.B.'er to make a video to show it doesn't matter. I set it up with an oscilloscope, r.f. pick up meter at the dummy load of a 50 Ω carbon resistor, different lengths of coax and no reading changed. Oscilloscope 50 Volts each time and the pick up meter did not change. I then proved putting the SWR meter could go anywhere. I need to see if my camera has enough memory as it's quite old and the new cards don't work in it. G4gHB.

Intuitively, it's gonna spin around 50 ohms.

Are lossless lines possible?

first !

A little more light let in. Thanks