#1468

Рет қаралды 4,638

Жыл бұрын

Episode 1468
let's take a look a bunch of cables
here is another way to measure loss: • #564 NANOVNA Coax Loss...
Be a Patron: / imsaiguy

Пікірлер: 48

@MikeFikes Жыл бұрын

Nice to see the VNA out again, covering new topics!

@owenkegg5608 Жыл бұрын

I love that display so much. Would fit right into a sci-fi. The computer startup in the beginning of Alien comes to mind.

@rogergreenwood1536 Жыл бұрын

Great to see all the SMA nut widgets in use

@hamradioeconomystyle48 Жыл бұрын

All right. I just bought some coax to replace some old. (Maybe about 20 years old) similar coax. After replacing the old cable I see very little, if any change in antenna system performance. I think I wasted my money. Now I can run this test to see if I needed to change the cable.

@BryanTorok Жыл бұрын

And, come back and let us know the results. I've been thinking of replacing a 20+ year old Comet antenna and coax.

@MaxPivovarov Жыл бұрын

In most cases, if water did not get into the cable and the cable itself is made qualitatively, then it can work 50+ years without a large loss of quality.

@Dieseleux Жыл бұрын

In extrem case, low PIM dummy load are made with very long lossy coax... and on your display, mostly all in the center of the chart.

@jluke6861 Жыл бұрын

Thank you.

@aneeshprasobhan Жыл бұрын

that's a nice vna. Do you recommend buying an old vna and calib kits if i do some 2.4GHz antenna matchings once in a while ?

@IMSAIGuy Жыл бұрын

this VNA only goes to 1.3GHz, for 2.4GHz look at: kzfaq.info/get/bejne/prualcqf27fDlIE.html if you are rich and have the room in your lab, an old VNA is a pleasure

@wiwingmargahayu6831 Жыл бұрын

nice time spending Sir

@Kirill_Maker Жыл бұрын

Nice 3d printed SMA handles

@IMSAIGuy Жыл бұрын

kzfaq.info/get/bejne/eJeYZK6bkrTLg6s.html

@TonyBarr99 Жыл бұрын

What specification defines a cables lossiness? Does the VNA output this value for comparison with the spec (if there is one)?

@IMSAIGuy Жыл бұрын

kzfaq.info/get/bejne/o7tnZNV4urHQcn0.html cable loss is usually measured in dB loss per 100ft

@TonyBarr99 Жыл бұрын

@@IMSAIGuy ,thank you!

@Mooff2 Жыл бұрын

You should tell us more clearly why length matters and how each cable measures in dB/meter.

@IMSAIGuy Жыл бұрын

ok, longer is more

@robinbrowne5419 Жыл бұрын

More wizardry. The screen looks like something Merlin would have had :-)

@techodisha4836 Жыл бұрын

looking at the thumbnail I thought he was hacking nasa

@BryanTorok Жыл бұрын

Near the end, you show the wiggle that varies with frequency. Since, as we travel along the transmission line we will see short and open at quarter wavelength intervals, shouldn't we expect to see more wiggles displayed with the short cable versus the longer cable? So the number of wiggles is really only related to the length of the cable. The vertical size of the wiggle would be related to the loss.

@IMSAIGuy Жыл бұрын

you get the wiggle every time it goes around, so more length more wiggles

@alioalio-cl6zk Жыл бұрын

I am a beginner and I want to learn and I am trying hard to learn, but my capabilities are limited. Is it possible to help?

@IMSAIGuy Жыл бұрын

here are free books: kzfaq.info/get/bejne/m6h7hcSlnJi4dIk.html

@fredflickinger643 Жыл бұрын

Paying for decreased capacitance and build QA!

@Champstarrable Жыл бұрын

Thousand of dollars for a coax? For what use case?

@IMSAIGuy Жыл бұрын

making critical measurements in a calibration or R&D laboratory

@PaulaBean Жыл бұрын

RG58 is not meant to be used at these high frequencies.

@IMSAIGuy Жыл бұрын

indeed. 21.5 dB loss per 100 feet at 1 GHz I have to add though, everyone is using RG174 which is worse!

@jeffreyyoung4104 Жыл бұрын

It really depends on the length of the coax. Lossy coax will still carry a usable signal when the length is short, but try it through a 100 meter length, and that will fail to carry enough signal for most applications, at high frequencies. If you are making measurements, it can be any short coax for the connections, as long as you know the loss of that piece of coax and can take it into account when making the measurement. What can make the process difficult, is when the coax is intermittent.

@IMSAIGuy Жыл бұрын

you are right, I was surprised to see such large effects with the short cables I was testing.

@paulcohen1555 Жыл бұрын

But can you actually measure the loss as in the title or it's just an qualitative way for looking at the cable?

@IMSAIGuy Жыл бұрын

I'm sure there is a way to back that number out, but you are better off using kzfaq.info/get/bejne/o7tnZNV4urHQcn0.html

@JimAndyAllyn Жыл бұрын

What a waste of time. The title of this video is "Coax Loss measured on a Smith Chart." You showed on a Smith Chart that there is loss in coax, but you never actually measured it, you never quantified it in any way. After eight minutes and 10 seconds, you finally changed to a log mag display where the actual loss of the coax (actually, twice the loss of the coax) is displayed. You owe me - and everybody else that wasted their time - eight minutes and ten seconds of time. Thumbs down.

@IMSAIGuy Жыл бұрын

I already made a video on the actual measurement: kzfaq.info/get/bejne/o7tnZNV4urHQcn0.html this is an easy way to check your cable on S11 without having to change the setup for S21. Sorry you didn't find it useful. take a look at the other video

@JimAndyAllyn Жыл бұрын

@@IMSAIGuy Sure you can check the loss of a cable with magnitude of S11, no need to set up for S21, and there's no need for the Smith Chart. I was doing that 40 years ago. The point is that this video does not show what the title says it will show. You could use the radially scaled parameters at the bottom of the paper Smith Chart - RTN. LOSS [dB] is there, and I see ATTEN. [dB] is there too, although I've never used that one. I saw the title of this video and thought I might learn something. I was disappointed. And I suspect I'm not the only one.

@IMSAIGuy Жыл бұрын

OK, fair enough, do a video and I'll point to it

@JimAndyAllyn Жыл бұрын

@@IMSAIGuy I might.

@stevecarlisle3323 Жыл бұрын

If you do not get any value from his video, s ,then WHY watch them.🤔