What do we measure in the picture? What is inside the blackbox ? - Page 1
Forum section: electronics / beginners

author: afganec123
author_rank: Newbie
timestamp: May 13, 2015, 08:26:05 am
content: Hi,we had to measure a blackbox with E5071 Network analyzer and now we should be able to tell what is inside this black box from the measurement. The output from the E5071 Network analyzer will be shown here.http://www.qooql.wz.sk/x.jpgIs there any way to figure out what is inside the black box from the picture ? What is it so ?Thank you for answers

author: mcinque
author_rank: Unknown
timestamp: May 13, 2015, 11:36:13 am
content: I sniff homework...am I wrong?

author: Delta
author_rank: Super Contributor
timestamp: May 13, 2015, 11:57:09 am
content: Did you not pay attention in class?

author: max_torque
author_rank: Super Contributor
timestamp: May 13, 2015, 12:04:06 pm
content: I bet there's a cat in the box!The more important question is whether than Cat is Dead or Alive??

author: BradC
author_rank: Super Contributor
timestamp: May 13, 2015, 12:16:38 pm
content: Quote from: max_torque on May 13, 2015, 12:04:06 pmIt's dead like all good cats should be.

author: afganec123
author_rank: Newbie
timestamp: May 13, 2015, 01:44:40 pm
content: Quote from: mcinque on May 13, 2015, 11:36:13 amIt is definitely not a homework. Someone asked us, what is inside the black box... And I am curious, so I am asking here if someone could know it ... Instead of sniffing , you should give me a serious answer. And if you don't know , just stay silent. As far as I am not interested in this "kind of science", i do not know the answer. Anyway thank you for your answers ladies.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 13, 2015, 02:06:53 pm
content: the purpose of "black box" concept is not to sniff what exactly inside, the purpose of it is so you can design your circuit based on the IO behaviour or model that black box with other components that produce almost the same result. so the wrong question is "whats inside?" and the wrong answer is probably doraemon or pokaemon. you asking like an illusionist put something in a box only leaving a tiny bit of it outside and ask what is it? quiz time anyone who answer correct get the prize. the only way to know whats inside is to break the box, no lucky draw game...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 13, 2015, 02:11:02 pm
content: Quote from: max_torque on May 13, 2015, 12:04:06 pmCat yes, but "5" seems more likely than DOATim

author: afganec123
author_rank: Newbie
timestamp: May 13, 2015, 02:28:58 pm
content: ok thank you for your answers guysEnglish is not my mother tongue. As far as i can see, the best answer to newbie (or person who is not experienced)is to tell what is wrong on his question etc ... Homework... Bla bla bla. I am not going to read this topic anymore. You can delete this topic

author: ConKbot
author_rank: Super Contributor
timestamp: May 13, 2015, 04:30:08 pm
content: Given the constant delay and low return loss, I'm gonna guess about 0.75-1 meters of coax.

author: Delta
author_rank: Super Contributor
timestamp: May 14, 2015, 01:01:19 am
content: Quote from: afganec123 on May 13, 2015, 01:44:40 pmMy mistake, please accept my apologies.So you were just sitting in the pub with your network analyser, and some bloke asked you to work out what his mystery circuit consists of... Happens to me all the time...

author: afganec123
author_rank: Newbie
timestamp: May 14, 2015, 02:42:35 pm
content: Jesus Christ came down from the sky and asked me what is inside the black box. And yes, you are right , i was in the pub sitting there with my network analyser. I hope, you've got your answer now, and you will be able to sleep during the night like you used to. I am glad to hear that i am not alone in the world, who has such experience with pubs.

author: ConKbot
author_rank: Super Contributor
timestamp: May 14, 2015, 05:18:31 pm
content: I wouldnt mess with this guy, a 5017 is a big damn network analyzer to be carrying to the pub. He could could probably wreck anyone in there

author: G0HZU
author_rank: Super Contributor
timestamp: May 14, 2015, 06:37:08 pm
content: Assuming the answer is going to be a simple one then I'd say there is about 80cm of coax cable that is shorted at the far end.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 14, 2015, 06:47:38 pm
content: Quote from: afganec123 on May 13, 2015, 01:44:40 pmIf you had been using a forum like this for any length of time, you would know that it is not unusual for students to come to these forums asking homework questions because they don't know the answer (or how to arrive at the answer). It is fine to help someone understand HOW to do something but it is NOT appropriate to blindly provide students with homework answers because they are not learning how to do it themselves.There was nothing in your question to indicate that it was anything but a typical homework or lab assignment, and it is inappropriate for you to get all huffy about @mcinque's reply. People are generally gracious and helpful on these forums, and you are a newcomer who we don't know asking what looks very much like a homework question.

author: G0HZU
author_rank: Super Contributor
timestamp: May 14, 2015, 07:00:30 pm
content: If it's a more complicated answer then maybe it's a 9th order Bessel (lumped) LPF with cutoff frequency = 100MHz with the far end shorted?But realistically, I think it will be a piece of coax cable with a short at the far end. So that would be about 80cm of typical coax cable (with velocity factor = 0.66) with a deliberate short circuit across the cable at the far end of the cable.

author: ConKbot
author_rank: Super Contributor
timestamp: May 14, 2015, 09:54:40 pm
content: +1 to shorted length of transmission line, just hooked a meter-ish long piece of coax to a VNA, shorted the end and got basically the same result, group delay about the same, 180 degree phase shift, and relatively constant loss.Only 0.2 dB of loss (.955 converted), 80 cm of cable (160cm effective) or .125 dB/meter, 12.5 dB/100 meters @ 50 MHz or 3.8 dB/100 ft @ 50 MHz, means youre probably looking at RG-58 or similar.You did cal out your test lead right? We're not all here staring at the test lead with a short on the end?

author: G0HZU
author_rank: Super Contributor
timestamp: May 14, 2015, 11:38:20 pm
content: QuoteYes, that would be funny if the black box was just a short circuit inside and they didn't calibrate out the 80cm test cableMaybe it was like this scene from a typical VNA theme pub below...

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 15, 2015, 12:23:29 am
content: Quote from: G0HZU on May 14, 2015, 07:00:30 pmis it "realistically practical" for a box that you cant open to contain 80cm of shorted coax?if anything, what is it for?

author: G0HZU
author_rank: Super Contributor
timestamp: May 15, 2015, 01:52:12 am
content: Quote from: Mechatrommer on May 15, 2015, 12:23:29 amI can only guess what is in the box based on the data provided. But yes, it is practical to have shorted coax in a sealed box if you want to make a stub filter for example.

author: baoblackcoal
author_rank: Newbie
timestamp: May 15, 2015, 01:55:38 am
content: pay attention in class plz.

author: ConKbot
author_rank: Super Contributor
timestamp: May 15, 2015, 01:58:50 am
content: @Mech, Given that the return loss is 0.2dB, the end of the transmission line is effectively short or open, the 180 degree phase shift indicates a short (open would start near 0), and the constant group delay across frequencies means its either a very very well built lumped sum delay line, (with a shorted output) or a length of transmission line. Walks like a duck, talks like a duck, till I hear otherwise, I suspect the duck is a witch.If said black box is a piece of RF equipment, and indeed the test cable wasnt cal'd out, and an input amplifier went short, even if it was AC coupled with a large enough coupling cap, you'd get exactly what is being seen here. Or if said box was quite large, and had coax meandering though it to get to where it needed to go, there could easily be 80cm of coax.

author: mcinque
author_rank: Unknown
timestamp: May 15, 2015, 12:01:58 pm
content: @afganec123 your "gimme the reply or f**k you" attitude will surely give you a nice futureI have a lot to learn.