#368

Episode 368
Return loss and VSWR compared
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[@haramanggapuja]

Wow! Nice. I just got the NanoVNA-H and stuffed it on my homemade mag loop. Verrrry interesting plots. And now I can begin to understand why the X5105 says the SWR is one thing and the VNA says the plot looks like I should never get on the air ;-) (Wish I'd had one of these toys starting out six decades ago. I might have gone into engineering instead of linguistics ;-) )

[@luigithebaker]

I had the same thoughts at first. I had to make sure I recalibrated it or recalled a previous calibration before taking a measurement. If you just turn it on it defaults to a non calibrated state and gives some erroneos readings. I did this with my first vertical antenna and the VNA said 1.1:1 swr but my radio was saying high swr. Calibration was off. I thought I was doing the right recall proceedure but I was really hitting the wrong button it turns out. Just a tip!

[@vidasvv]

Nice explanation! I I never even heard of "return loss" until I got a hold of an old HP-8712ES VNA about 10yrs ago, SURE OPENED MY EYES ! LOL 73 N8AUM

[@shanerorko8076]

When the lines are at the top=, bad; when the lines are closer to the bottom= better, whichever units you're using.

[@w2aew]

To be perfectly pendantic - the LOGMAG of the S11 on CH0 of the VNA is actually the log-magnitude of the REFLECTION COEFFICIENT, not Return Loss. Strictly speaking, Return Loss is a positive number - i.e. the greater the number, the greater the "loss". If you simply change the sign of what you're reading, you get Return Loss. Return Loss = -(Reflection coefficient or S11). The terms are used interchangeably. You've correctly referred to Return Loss as a positive value, but the nanoVNA displays and plots the LOGMAG of S11 which is the Reflection Coefficient.

[@IMSAIGuy]

Thanks Alan. Your comments are always welcome

[@w2aew]

Ha, should’ve been pedantic

[@w2aew]

@@user-lp3cf5yn5b A very low reflection coefficient like that is good. It means there is very little energy being reflected.

[@w2aew]

@@user-lp3cf5yn5b Based on the picture you emailed, there really isn't much to be concerned about. -45dB ref coef is still quite good. Looks like you have your transmission line terminated (based on the smith chart). The dips at 2.8 and 8.2m don't really indicate anything significant.

[@w2aew]

@@user-lp3cf5yn5b Have you seen my playlist of VNA videos? kzbin.info/aero/PL4ZSD4omd_AylEyNCQYR3RcEb0olukPEJ

[@timke8ldt354]

Great Job. Now I have a better understanding

[@mitchellmoss]

Great explanation. I've tried to understand the difference between these two things. Looks like they are the same thing with different scales. Nicely done.

[@ralphmowery2898]

Right, they are execally the same thing in different units. You might think of it in terms of money. If I give you two paper dollars and 200 pennies. You go to the store and either one will get you the same item. Or if you get one quart of milk or 1.05669 liters of milk, you have the same amount.

[@Gw0wvl]

That's why I went for the F version as it's a fair bit bigger , Much easier to use .... Regards de 'Gw0wvl' 👍

[@theunconventionaldeal3879]

Swr is just a visual representation and simplification of return loss as measured by a simple and cheap meter, Hence why it's a popular measurement.

[@IMSAIGuy]

It is voltage measurements not power measurements making is easier (cheaper)

[@stephenjones9153]

I have always hated dBs as it never seems to make much sense to me, for instance how is 46dBs of return loss better than 6dBs ...I find it much easier to work in power loss in Watts, for example TX puts out 100 Watts and you lose 10 watts so there's 90 Watts going out the Antenna...rather than 46dbs loss with 6dbs going out which doesn't make a lot of sense to me. Glad to see even the Experts having to use a Table to work out what the dBs mean in swr terms.

[@benmeadors6799]

Love the videos and information. I'm curious, what kind of clamp you're using to prop up your Nano VNA here?

[@IMSAIGuy]

it is a kant twist clamp

[@pirate959]

Stay in SWR units. Most people cannot think logarithmic, the swr plot visually makes it obvious. Also, all radios are going to provide this and novices understand.

[@DartRM27]

Hello, I recently purchased a litevna64 to measure FPV drone antennas. Do I understand correctly that -30 is better and -5 is worse? What numbers are good and bad?

[@IMSAIGuy]

yes -30 is better. you want at least -20 for a good antenna

[@IMSAIGuy]

kzbin.info/www/bejne/ZnjVfnx9dt55i6csi=VOGwFwy7gjinc3AO

[@DartRM27]

@@IMSAIGuy thanks 🙏🏻

[@TheScottClifton]

Do you have, or could you do a video on what happens to reflected power? There are too many folks claiming SWR finds its way to the antenna and is getting radiated, not lost. Sure, the radio can also reflect power coming back toward it, too, but the chances are the combination of transmission line and radio amplifier output network losses are wasting most if not all of that power. You have great ability to show many things with your vast test instruments, can you show what happens to reflected power in a typical ham setup?

[@compsmith007]

So. This is a ferocious quibble over a comma? Yeah, there's value in understanding both arguments, but the desired results is what matters.

[@amlopex]

Hello! Nice video, thanks a lot. Now, which firmware version did you use to do the video, the "aa" DFU or the "ch" DFU? The "aa" device firmware update (DFU) is known as the Antenna Analyzer version. Can you tell us if you did use that one or did you just use the default one? Thanks!

[@IMSAIGuy]

used the aa. both use the same data just plot it different

[@kchoudri]

hi, I am new to VNA world,,, and I really appreciate you sharing very useful knowledge with the VNA NEWBIES like myself. what I want to know is can this vna also be used to measure the output power of the ham radio devices?

[@IMSAIGuy]

no

[@kchoudri]

@@IMSAIGuy Thank you for your brief answer :-)

[@ralph9987]

Brilliant video, thanks

[@ralph9987]

Ps, some of these units are being sold as 1.5ghz units. What needs to be done to them to get that extended freq. range? Tia

[@jimw7ry]

Cant see your screen or document your looking at. :(

[@kasperdasradio]

Hi @IMSAI Guy, i was wondering why the return loss is presented on the NANOVNA in a negative value (-12db) Because the cheat sheet do not present RL in negative values...

[@IMSAIGuy]

I've seen it both ways. Nice to have the negative sign so you don't confuse gain and loss. +10db gain. -10db loss. Otherwise, if it is understood to be a loss then no sign is needed.

[@romario21]

how do you display the vertical grid lines?.I only have horizontal lines on mine.thanks

[@IMSAIGuy]

that does not make sense to me. what is your start stop frequency range?

[@Davidsmith218]

On my vna I have a return loss of 32ish db and a 1.06ish swr on the input of my amplifier so this is good. ?

[@IMSAIGuy]

sounds very good

[@thomaskallmyr]

INTERESTING ABOUT NANO VNA😮😮😮😮😮

[@LarryMassey]

Good job.

[@SuAmigoElilegal]

Can you check the gain of the antenna ?

[@scharkalvin]

so I guess a perfect 1:1 match equals an infinite return loss.

[@IMSAIGuy]

yes minus infinity db you will be limited to the noise floor of the instrument. 70db 0 to 300mhz 50db 300 to 600mhz 40db 600 to 900mhz

[@ralphmowery2898]

Very doubtful you will ever see it in real life. However if all the power is absorbed by the load there is nothing to come back to be measured. You may get so close that the instruments can not show it.

[@itdevops]

hi, ty for your video. i want buy one but how & we can see frequency resonance of an antenna ?? ty

[@IMSAIGuy]

the frequency resonance will occur at a low return loss. So I look at return loss trace and set a marker. move the marker to the dip in the return loss and the marker will read out frequency. or use SWR trace if you like that instead.

[@itdevops]

@@IMSAIGuy ok, ty & sy i have see your video on bad antenna & good and it's explain I just ordered one at the moment TY ;) fast reply wow +++

[@vidasvv]

Resonance occurs when j=0 (s11)

[@steveo4233]

I'm always troubled by people who use db as a thing. "DBs" is not a thing that flows out or bounces back. Energy is a thing. Energy, measured as power, voltage, or current is what is flowing out and/or reflecting back. DB is a ratio of two things (power, voltage etc.). At 1:19 you say, "how many dbs come back?" That is a nonsense question. DB is not coming back. The return loss at the input is the ratio of the power going out (forward) to the power coming back (reflected) and is measured in db. It's a ratio, meaning the reflected power divided by the forward power. Power / Power (or voltage, etc.) means the units cancel an you are left with just a number. And that number is not going out or coming back. It's the combination of both, not one or the other.

[@IMSAIGuy]

saying how many db is coming back is like saying what percentage is coming back...

[@OwenDuffy]

The formulas given at 3:41 are both wrong.

[@h.sapienstechnologicus8865]

1:12 SWR measurements are kind of a weird thing, Return Loss is just DB's 6:00 SWR 3:1

[@clems6989]

Point ?

[@h.sapienstechnologicus8865]

jeez, why can't we just express these arbitrary values in percentage of transmit effectiveness? Like: at SWF of 3:1, 25% of energy is reflected back.

[@chrisloh745]

because that would be too easy

[@volkerblock]

50 years I used SWR, now I use return loss. But nobody likes it, boo hoo.

[@Aleziss]

what does return loss tells you more than swr ?

[@volkerblock]

@@Aleziss Nothing! But if you use return loss ( see the video) , why should you change to SWR? Because your ( and my) old amateur eqipment uses SWR? In Smith Chart its good to use SWR.

[@volkerblock]

kzbin.info/www/bejne/o6eyZ5momLp3pZI look here

[@Aleziss]

@@volkerblock oh ok... I thought there was an advantage to read return loss instead of swr...

[@jbx907]

Can this nanovna tune a duplexer?

[@IMSAIGuy]

I would think so

[@ralphmowery2898]

Yes it can with the one problem . If a duplexer has more rejection than the nano can resolve you run out of 'head room' . That is if the nano puts out -20 dbm of power and the receiver part is -100 dbm you have 80 db of range. If the duplexer has a rejection notch of less than 80 db you are ok to go. The better duplexers will have over 90 db of rejection, so you will not be able to get a good notch adjustment.

[@Aleziss]

I wonder why there is no return loss meters then along with meters in radios...

[@vijovame]

Probably because is easier to read 1.02 vswr than 40.086 loss? I have an antenna analyzer and I had no idea how to use the vna part of it... until now

[@Aleziss]

@@vijovame I guess it is easyer to see a bar graph getting as low as possible vs another graph going as high as possible by fallowing your comment. May I ask what antenna analyzer you have ?

[@vijovame]

@@Aleziss I have 2, I built the EU1KY analyzer and I purchased a MINI1300.

[@Aleziss]

@@vijovame the EU1KY is NOT the nanovna right ? they are different devices ? how do you like the mini1300 ? that newest one has a VNA port which the 600 did not. Are there softwares for the mini1600 ? I am really "afraid" to invest in those analyzers, first, I know nothing about them and how to get my way around (can't even understand a smith chart) and two, there seem to be sooo negative comment about the quality and precisions of these chinese vna analyzers... it's either really cheap or quite expensive like the minivna pro at 600$. I understand that 600$ is not expensive for a VNA but it is for someone like me who is not a RF technician and use this tool not really often beside testing antennas and measuring baluns...

[@vijovame]

@@Aleziss I like the mini1300, it has a lot of functions on it, a metal case and includes a rechargeable batery, but I did the same analyzer with some parts and works the same but no battery, you can see the EU1KY AA and best firmware here: kzbin.info/door/z0x9-5AH4_A_nhiAp1HXdw The mini1300 can use the same firmware as the EU1KY AA. Webpage is on the description in the videos from Ian. Good luck. Edit: no, EU1KY is not a nanoVNA

[@OwenDuffy]

... I should have said inconsistent with your video.

[@OwenDuffy]

Some more detail: |s11|dB=-ReturnLossdB in the real world, hams tend to think -ve ReturnLossdB is correct. The plot you point to when talking about ReturnLossdB is |s11|dB, and it is -ve. The second formula is correct stand alone in the real world, but if you take ReturnLossdB to be -ve as you infer when referencing the VNA, it will give the wrong result.

[@shadimurwi7170]

Anritsu Sitemaster

[@DanBeauvoir-uo7yc]

You never actually showed how to

[@IMSAIGuy]

I have a 'nanovna' playlist. you will find lots of videos

[@bruceblosser384]

The Return Loss seems to be totally ass backwards!!!!! Why the hell would a lower SWR have a higher return loss? This makes NO sense! No wonder ham radio uses SWR!!! :)