Equivalent of the TPPep cable for testing devices for transmitting video signals over a twisted pair cable.
To assess the quality of the equipment designed to transmit video signals over a twisted pair cable, full-scale tests are often used using coils of this cable.
In addition to the fact that the electrical characteristics of the unrolled cable and the cable rolled into a coil differ significantly, there is an obvious inconvenience for conducting such tests: despite the clarity of such an experiment, to conduct it (at an exhibition, in the office, at the customer's), it is necessary to actually have coils of cable of this length.
At the same time, in radio engineering practice, for measuring equipment parameters, not the medium itself is used, but the equivalents of the signal transmission medium (antenna equivalents, long line equivalents, etc.), which are standardized and generally accepted. For example, instead of a coaxial cable, an artificial long line is used, consisting of capacitors and inductors equivalent to the action of the linear capacitance and linear inductance of the cable at a given length.
I propose using a similar approach for cables of the TPPep type, which have the following linear parameters http://centercable.ru/catalog/telecable/20.htm
In addition, there is also the capacitance of the cable cores on the screen, which must be taken into account if the screen is grounded. This capacity is usually not standardized, but in practice it exceeds the working capacity by 40–50% http://izmer-ls.narod.ru/emk.html Based on this, the calculated values of this capacity were obtained (Table 3).
In practice, it is considered that an artificial long line is similar to a real long line if the number of links exceeds 4. Thus, using a similar approach, a simple electrical circuit can be used as an equivalent of a TPPep cable, consisting, for example, of the following 5 links for the case of using a twisted pair cable without a screen (Fig. 1):
Fig. 1. Electrical circuit of the equivalent TPPep cable (without shield)
When using a cable with a shield, the circuit will look like this (Fig. 2):
Fig. 2. Electrical circuit of the TPPep cable equivalent (with screen)
Since the linear parameters of the cable are directly proportional to its length, then in any case one cell of such an equivalent will correspond to 1/5 of the length of the twisted pair cable. For example, with a cable length of 1000 m, the electrical parameters of one cell simulate 1000/5 = 200 m of cable length.
So, to obtain the resistance values of the resistors R, simulating active losses in a TPPep cable 200 m long, it is necessary to divide the values of the linear resistances in Table 1 by 5:
To obtain the values of the capacitors Cp, simulating the working capacitances of the TPPep cable 200 m long, it is necessary to divide the value of the linear working capacitances in Table 2 by 5:
To obtain the values of the capacitors Ce, simulating the capacitance of the cable cores on the screen with a TPPep cable length of 200 m, it is necessary to divide the value of the linear capacitances on the screen in Table 3 by 5:
Table 6
Important notes
1. The obtained values of radioelements correspond to the TPPep cable of 1000 m in length. To simulate a cable of arbitrary length, the obtained values should be recalculated proportionally to the required length in relation to 1000 m. For example, to simulate a cable of 500 m in length, all ratings of radioelements should be reduced by 2 times, and for a cable length of 2000 m, all ratings should be increased by 2 times.
2. If there is no resistor or capacitor of the required rating, a series or parallel connection of radioelements can be used.
3. If you want to achieve greater accuracy in approximating the equivalent to the actual parameters of the cable, you can use a circuit consisting of a larger number of cells (>5).
4. To reduce the signal «slippage» from the input directly to the output, it is recommended to install the circuit «in a line» along the signal propagation path.
5. Since the capacitance of the TPP cable cores to the screen is not standardized, the value of the capacitor capacitance Ce may require clarification by experiment.
6. To obtain a tunable equivalent of a cable, a cascade connection of several equivalents can be used.
7. A similar approach can be used for other types of cables, based on their linear parameters.
Conclusions
1. The creation of the described equivalent of the TPPep cable, consisting of a small number of radio elements, allows us to solve the problem of prompt and objective testing of the quality of operation of various devices for transmitting video signals over a twisted pair cable.
2. Such an equivalent is a light and miniature device that can be made in a few minutes and which can be taken with you on a business trip, to an exhibition, etc.
Fragments of a discussion on the portal «Bridge of Safety»
Pavel aka Spiridon:
Who would make a prototype? Well, it would also be reconfigurable for different lengths, like capacitors and variable resistors, plus disconnectable/connectable cells.
Yuri Gedzberg:
Such a complex task requires special knowledge and training; in extreme cases, it can be entrusted to your son, but only if he already goes to school (after all, you need to solder 10 identical resistors and 5 identical capacitors!).
Why rebuild to different lengths? At exhibitions, cable coils are often rebuilt? But you can switch (take several equivalents, for example, 500 m and switch to your heart's content: 500 m, 1000 m, 1500 m…).
Or you can solder a 2000 m equivalent, put it in your pocket and come to the exhibition. And then — just walk around the exhibition, ask to connect it at the stands and see with your own eyes the quality of devices for twisted pair cable from different manufacturers.
In any case, now they won't deceive you: you are engaged in the sale of equipment for transmission via twisted pair — well, put up a real stand with a real length dialed, and not empty boxes with stubs of twisted cable: deception, deception, deception all around, said the hedgehog, getting off the cactus…
Pavel aka Spiridon:
If the device has a length calibration, then it will practically be a device for testing transmission equipment via twisted pair. And this is a wider range of applications…
Vizir:
Aha, the «prayers of the deaf province» have been heard. Here it is, the solution — on the surface, and its name is equivalent. I soldered it myself when I was setting up the transmitter, so as not to confuse the world community with modest 200 watts and my hoarse «Hello, one, one» on the air. It's a pity I don't have a vitotransmitter at hand now, it's a pity cubic meters of radio components are lying in the old apartment together with the radio station and a pile of measuring instruments. I remember I had a treasured case, made from a single piece of aluminum by a skilled turner — there were exactly six compartments for the IF filter!!! Who said that Monday is a hard day? — to make, to check (after all, comparing with the real length of the cable) Eh? Or was it my mood after Saturday's hunt that was so uplifted — I took a black grouse and a bag of whites to the delight of my mother-in-law
dragged P.S. The cells need to be shielded by soldering a case, for example, from foil-clad fiberglass (the most offensive thing is that it lies there, dear, cut into 30 mm strips for making cases for all sorts of experimental ones). It is not recommended to reconfigure the variables R and C for different lengths, but connecting additional cells is simpler and more correct. And it is better and more honest to make equivalents for fixed lengths. The lengths should be 500, 1000, 1500, 2000 (rarely) — really in-demand footage. Even I myself became interested — should I drag my old X1-50 to work? 73!
Yuri Gedzberg:
Dear Vizier!
With shielded cells everything is correct, but keep in mind that the shields will work as shields only if they are grounded. If they are not grounded, the signal «penetration» may be no less, but even more. If you mount them in a «line», then at frequencies up to 5 MHz, shields may not be needed
Dear Pavel aka Spiridon!
It is quite possible to make a reconfigurable device (like sets of resistors — measures for calibrating measuring devices). Yes, too many switches and radio components will be needed. Of course, there is a solution here — active keys in each cell, resistors weighted according to the R-2R law, but this is very difficult (at least at this stage).
But what I would like to draw attention to is that although there are more and more programs for determining the focal length of a lens, they somehow do not leave the market and new cardboard circular calculators for solving this problem appear periodically. And it is not only about simplicity and ease of use — manufacturers of lenses and video cameras have long understood the benefits of demonstrating their honesty in solving this issue and are trying to lure customers to their side in this manner.
Which of the manufacturers of devices for transmitting video signals over a twisted pair cable realizes this simple truth and starts giving away such equivalents (with their logo) for free at exhibitions, that is the winner.
Popov Alexander:
There was an attempt. The task was set for those who had been dealing with equivalents their entire lives. They estimated and calculated. The equivalent would have cost twice as much as the cable itself. Well, and from the point of view of clarity for the client, the equivalent does not work at all. They believe the «live» immediately. So the coils lie under the table, switched every 100 meters. In the coil, the conditions are indeed harsher. But if it works in harsh conditions, then it will work even more so in comfortable ones.
Yuri Gedzberg:
Alexander Leonidovich!
I suggested using an equivalent 3 years ago.
«If we want to not surprise the client (that time has passed), but strictly demonstrate the capabilities of the devices, it is necessary to introduce into testing the equivalent of a twisted pair cable (a box with radio elements corresponding to the concentrated parameters of the line used).» http://forum.security-bridge/forum/2/3638/?page=2
Of course, it is your right to decide how sales should be carried out in your company — «live» or «in the dark».
However, knowing your authority in our market, I understand that your opinion can be interpreted as a final diagnosis for many. Therefore, I will allow myself to disagree with you.
1. «The task was set for those who have only dealt with equivalents their entire lives.»
I do not know of any field of knowledge where equivalents have been dealt with all their lives. I hope this is not a top-secret organization, please name it.
However, I know the laws of electrical engineering and radio engineering, and for me this is quite enough, so no authorities are scary.
2. «The equivalent would cost 2 times more than the cable itself.»
It seems that you can find a good cable supplier.
Please type «radio components» in Yandex and see that resistors cost 15 kopecks apiece (well, a ruble). Capacitors — somewhere around 3 rubles (you can find cheaper). Total components at most: 1 ruble x 10 + 3 rubles x 5 = 25 rubles.
So, taking into account the difficult economic situation in the country and understanding its responsibility in the area of cable equivalent, the company «Bridge of Safety» solemnly opens a credit line in the amount of 25 rubles to everyone who brings to our stand at the Sfitex exhibition a cable equivalent, personally annotated by the visitor or his child according to the scheme http://articles.security-bridge/articles/16/12303/
3. «In the bay, the conditions really are tougher.»
I do not agree with this either, I can only repeat that «the electrical characteristics of an unrolled cable and a cable rolled into a coil differ significantly»:
in a coil, it is possible for the signal to «slip through» from the input to the output (they are quite close), i.e. the result will be better than in reality;
transformer and capacitive coupling between pairs of one cable are possible;
a wire rolled into a coil can have significant inductance, the result of which is difficult to predict
So, I am not going to agitate anyone for the proposed solution, I just want to remind you:
«The verification method couldn't be simpler — a lit cigarette in the lens. Or a lighter. Like with glasses. Just take out the lighter, you don't even have to light it — the seller will immediately confess.»
Alexander Leonidovich! You said that http://forum.security-bridge/forum/2/15652/?page=1
I'm acting more humanely: I suggest using a cable equivalent.
P.S. Maybe we should recommend such an equivalent in GOST R 51558-2008, and that's the end of it? http://forum.security-bridge/forum/3/15372/?page=1
Mikhail Kamenetsky:
In order for an equivalent to replace a cable, it is necessary to create conditions under which anyone (everyone) will trust the equivalent.
And for this, the equivalent must be accompanied by documents that inspire confidence and undergo periodic verification in metrology authorities. In total, it turns out that the cable is cheaper, more visual and more accurate.
Yuri Gedzberg:
Mikhail!
Have you ever checked identity using the DNA method? But you trust it, right? No prophet in his own country? If someone does, everyone will follow him? By the way, in this case, the cable also needs to be verified.
«In total, it turns out that the cable is cheaper, more visual and more accurate.»
Cheaper — no.
More visual — yes.
More accurate — no.
P.S. What verification? I need to check the device without a coil — I go to the store, buy capacitors and resistors (they have permissible deviations indicated on them). We solder them and promptly check the device.
When you buy a capacitor in a store, do you measure its real capacity? Or do you still believe the marking?
P.P.S. We can still talk about verification when I present this device at the final inspection of my enterprise. And this is not even an incoming inspection. I personally soldered the parts and I went to the exhibition so that I (personally) would not be fooled here. What are we talking about?
It seems that our people have really forgotten how to hold a soldering iron in their hands. Or have gotten used to the fact that someone will come and give orders. We are generally incurious.
Well, instead of all this discussion, someone should have soldered the circuit and checked it. And said: «Yuri, I did as you said, nothing works.»
I would have been happy. Or someone would have said: «You drew the circuit incorrectly» — I would have sincerely thanked him (first, of course, I would have argued).
But arguing just like that, just to avoid doing…
Mikhail Kamenetsky:
Yuri Mikhelevich, the discussion seems to be in the context of demonstrating work on an equivalent.
We (me and the company I work for) actively use equivalents in our daily activities: when debugging and repairing products that use long communication lines. Working with an equivalent in a lab – yes. But at an exhibition… Personally, I don’t trust equivalents that someone else has made and uses to demonstrate the operation of devices. I will demand proof of trust. If I have my own equivalent – that’s a different matter. It’s easier with a cable – the one who exhibits less needs to explain it to consumers, he can play on the innate (or acquired) mistrust of engineers (visitors to the exhibition), he can contrast his products with those that work at the neighboring stand via equivalents, fueling mistrust towards him. A visitor will be more willing to trust a cable than an equivalent. It’s been proven.
Yuri Gedzberg:
Mikhail!
I repeat: we can argue here endlessly.
All radio receivers and transmitters are tuned using the antenna equivalent.
At UltraStar, when essentially only systems for transmitting video signals over twisted pair appeared, I also dragged coils. But that time has already passed – we need to call people forward, and not trick them with the tricks “The video signal went 1 km of cable”.
Either we raise the level of the market, which is not easy, we move forward, or we stoop to its most illiterate participants, flirt with them and get immediate success.
Popov Alexander:
Yuri Mikhelevich!
In general, Mikhail has said it all! At the exhibition, I need to be quickly and unconditionally believed. Without unnecessary proof of their rightness. By the way, the development of the equivalent for us was carried out by a truly secret (at one time more, now less) organization. Indeed, they worked hard with equivalents, because it could not be otherwise. But they did not have mass sales. They did not need to look for buyers in this way, they just needed to submit a government order. I remember, at one time at an exhibition, one competing company came to St. Petersburg with a kind of suitcase stand. Everything was in a case: a transmitter, a receiver and an equivalent. And we had coils of cable, under which the 45th angle bent when they were carried on it. The feedback from customers was unambiguous: «They have some kind of equivalent… What kind of equivalent is this, how do we know?» And after that we dragged these coils to Moscow under the swearing of drivers. Mikhail formulated the task absolutely correctly: it is necessary for the entire audience to believe in this equivalent. And this is impossible in principle. It is not a technical task at all. There are flight simulators that fully simulate all possible situations, but the pilot is assessed based on the hours of flight time «live». There are shooting simulators that imitate wind speed, and all possible target movement, even the type of cartridge and recoil. But competitions are held exclusively with live ammunition. How can you make a person believe in an equivalent? Honestly, I have no idea at all. And even specialists will always have a certain amount of skepticism, like, what if the specialist who made the equivalent did not take something into account. You show the diagram, but what if the real assembly differs from the presented diagram? These coils of cable at the exhibition — this was my separate idea. It works. I have not yet seen an equivalent «work». Even if they sold only the equivalents themselves, they would certainly drag the «live» cable to the exhibition again. So that there would be something to compare with, and not to believe. At least until the product is promoted. Can you explain to me what is my benefit from the equivalent? What will I get from this?
Yuri Gedzberg:
Alexander Leonidovich!
You and I are not competitors: you need people to trust you quickly and unconditionally, but I need people to trust no one, to trust only their knowledge, their experience — only then is it possible to move forward.
When you talk, for example, about buying a gun, underwater equipment, etc. and give examples of how they are trying to rip you off, you take the position of a buyer. Here, you are in a firm position of a seller.
Both you and Mikhail say: «so that the entire audience believes in this equivalent. And this is basically impossible.» Everything is wrong: if this is not actively resisted, something like this will happen sooner than you and Mikhail think.
In general, you trade in APV Yourselves, we trade in ideas, we have different businesses.
Popov Alexander:
Yuri Mikhelevich!
Well, the original is better than a copy. Why do people crowd around the Hermitage every morning, often preventing me from getting to work with the abundance of parked buses, instead of buying an album with reproductions and enjoying them, sitting by the fireplace. Just imagine the equivalent of a glass of vodka with a sandwich with sprats!!! In the form of, say, some kind of pill. They say the effect will be the same. People will definitely not understand and will not appreciate such a creation.
Rustam:
This equivalent also determines the transmitters' ability to correct signal attenuation frequency, but does not test their immunity to interference. If one transmitter has better immunity than another due to increased signal voltage, testing with an equivalent will not show this.
Yuri Gedzberg:
Alexander Leonidovich!
But how can you sell guns by demonstrating their quality with an equivalent like a target? I'm going hunting and want to test how I can shoot a duck, a squirrel, a fox with this gun, and you're slipping me some scrap of paper with concentric circles! Does a hare sit still when there's a hunter with a gun in front of it? Let it run around the basement!
You don't even notice that we use equivalents all the time in life. In Czechoslovakia, the quality of beer is tested by whether you can tear your leather pants off a bench with spilled beer or not.
In order to compare people's intellectual abilities, they came up with a universal equivalent — chess (and you, as a participant in the historical match, know this firsthand).
Don't be afraid of electrical engineering, that's the main thing. I will try to change the situation on our market with my new book.
And to bring the river to the horse, I announce our new campaign «Brain in safety». To exclude attempts to fool people, I will personally make an equivalent of a twisted pair cable for any company that will present its devices for transmitting video signals at the exhibition.
So, I am addressing all participants of the Sfitex exhibition. I ask you to indicate in this forum topic:
— the type of cable,
— its length,
— the time when visitors to the exhibition together with me will be able to compare the result of transmitting a video signal via cable and via the equivalent at your stand.
See you at the exhibition!
Re: Equivalent of TPPep cable for testing devices for transmitting video signals over twisted pair cable
Yuri Gedzberg [09/24/2008 14:08:44]
Rustam!
«does not check immunity to interference in any way. If one transmitter, due to increased signal voltage, has better immunity than another, testing on the equivalent will not show this in any way.»
But will the coil show it?
What does immunity to interference have to do with it? And the equivalent will not show immunity to lightning. To random actions of builders who are capable of breaking the cable. To the phases of the moon. To inflation.
It's boring, gentlemen.
That's why we have what we have and look with envy at foreign countries. The ideas of the Japanese and Taiwanese are snapped up like hot cakes. Whatever we come up with, we always say, «What will I get out of this?» And we don't do anything. But first we have to do something!