# Tag Info

63

The are called aeolean vibration dampers, or Stockbridge dampers. They aren't rigid weights: the weights vibrate on the ends of the centre-clamped bars. You can see the wavelength that they are trying to damp: it's approximately twice the distance from insulator to the damper. If the whole wire length is swinging, that's something different, and not what ...

42

Some repeaters have a model for the frequency-dependant characteristics of the cable (which varies with length), and pre-emphasize the signal in the output driver to compensate for those characteristics so that the signal at the far end comes closer to the ideal waveform. Such a driver can drive a longer length of cable than an uncompensated driver can.

34

The picture shows three common arrangements of wires. I added wire-to-wire capacitor symbols, note that you also have a wire-to-ground capacitance for each wire. Capacitor values decrease as the distance between the wires increases. Picture is own work, CC BY-SA 3.0 Case 1, Three wires in one level (equal distances to ground, but different wire-to-wire ...

32

These seem to be optical fibres. Figure 1. Close-up of fibres branching onto each of the lightning protection wires. Thanks to your high-res photo we can see the fibres at (1) and (2). Note that this pole is a "corner" pole so it makes a good place to join both the cables and the fibres as both would generally be pulled in straight lines. The fibres uses ...

31

Try not to fixate too much on the fact that these are vias in a PCB. The point is that they represent impedance changes in the signal's path. These effects are not unique to vias, they can be caused by many different signal path geometries. The titles under the graphs (on page 18, slide 36 of your linked PDF) tell which impedance change is most dominant for ...

31

There are several modes of vibration on conductors between poles. Different devices damp different vibrations. These weights are intended to primarily dampen torsional vibration. Torsional vibration is more closely linked to low frequency high amplitude oscillation - conductor gallop - versus the high frequency low amplitude flutter, which is more ...

29

OK, for what it's worth, here's how I visualize it. As you say, a transmission line has both distributed capacitance and distributed inductance, which combine to form its characteristic impedance Z0. Let's assume we have a step voltage source whose output impedance ZS matches Z0. Prior to t=0, all voltages and currents are zero. At the moment the step ...

26

Probably very little effect at all as long as the dimensions are small. Coming from the left hand side, there will be a reflection from point 'A' followed closely by an (almost) equal and opposite refection from 'B'. As long as the distance from 'A' to 'B' is small, these reflections will effectively cancel-out. As an example, let's say the impedance inside ...

26

I'm assuming you mean these two: The official name for these is "Distribution transformer". They are the "local transformers", here's a schematic of how they could be connected: Which is from this question Actual connections and voltages depend on the country so details may be different.

25

Your tooling seems to be the cause there, not the cable. From https://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=1428419&nid=-32775.536879654&id=1428419 The 4294A extends its measurement frequency range up to 110 MHz by terminating each measurement terminal with 50 ohm in order to eliminate the resonance of test leads (...

24

TTL (single-ended, unterminated) signals can easily handle 20 Mbps or more — look at SPI, for example. If you're only going a few inches, ribbon cable and IDC connectors (or a backplane of some sort) will get you from board to board. 1 Gbps puts you into the realm of having to deal with impedance-controlled traces, connectors and cables. The receivers ...

24

A few reasons: Power Faster speed means more power. Not only do you need faster analog circuits, which will consumer more power, all your electronics surrounding them need to be faster. Your digital systems, your latches, clock management, etc. If you get that 1 Gbps by using multilevel signalling you now need better ADCs and DACs. You might need to start ...

23

I think it's unfinished business. I'll get to that lower down. When you have a pole-to-pole run of delicate communications cable it needs to be supported in several places from a "structural" steel wire. The steel wire is suspended between the poles and is needed because the comms cable's own weight would inevitably cause it to stretch and fail. ...

20

Something as simple as a cable does not have discontinuities like that. There may be a clue in the fact the problem occurs at a nice round number, 5MHz. Is this a place where your test set changes ranges? Maybe it changes output amplifier, or filter, and one of them is broken or damaged. The fact that you've quoted measurements at 4.99MHz and 5.01MHz ...

17

Yes, there will be a brief pulse of current through the bulb as the portion of the transmission line (i.e., its capacitance) to the right of the bulb charges to the supply voltage.

15

There will be a slight current pulse at switch on even if you consider the circuit a lumped element circuit, i.e. without resorting to transmission line theory. Just keep in mind that in a real circuit stray capacitance is always present, therefore you might model the open end of the transmission line as a capacitor (with tiny capacitance, say ~1-10pF). ...

15

Reflections happen everywhere, not just in transmission lines. Transmission line is a model of the physical situation, which is easy to apply to a pair of conductors whose length is comparable to or larger than the wavelength of the signal, and which is regular in cross section. What determines whether reflections matter is the frequencies in and the ...

15

I'm pretty sure they serve a specific mechanic purpose, that nowadays is usually solved with Stockbridge dampers: They absorb the energy of mechanical oscillations in the line.

15

The large cylindrical devices as indicated below are power line transformers. Their function is to step down the higher distribution AC voltage down to the common mains line voltages that feed into residences and businesses.

15

While, in theory, high impedances would reduce power dissipation for the same voltage swing, there are several important issues in practice. 1) It's the power, not the voltage, of a signal that determines signal to noise ratio. If you must swing the full rail, then you'd win by increasing the impedance. However if you launch a specific power, then low ...

14

The obvious question is, "Does 1 Gbps mean 1000BASET Ethernet?" If that's what the customer is thinking, your requirement that, "we don't have room for things like magnetics" rules that out right away. Ethernet does use magnetics on the physical layer, and when I designed an interface some years ago the magnetics were part of a roughly 1 inch cube. You say ...

14

Shannon's Theorem sets the ultimate limit of information bandwidth on a cable. Here's some more info about that: https://www.gaussianwaves.com/2008/04/channel-capacity/ tl; dr version: the Shannon-Hartley Equation: $C = B \; log_2 \left( 1 + \frac{S}{N}\right) \;\;\;\;\;\;\;\;\;\; \rightarrow (1)$ Where $B$ is bandwidth in Hz, $\frac{S}{N}$ is the ...

13

The larger DT is 3 phase voltage stepdown, while the smaller one uses only 1 phase for local use residential use.

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A Bit of History The suggestions behind this topic go against what a lot of electrical engineers have been taught since their first circuits course - that AC is better for power transmission. After all, in the "war of currents" in the late 1800's, it was Tesla who helped Westinghouse fight for AC, eventually defeating Edison's dreams of a DC empire. The ...

12

You should not be surprised that they use different voltages and frequencies, you should be surprised that there are only two big voltage/frequency standards. When electricity was first introduced each producer provided a different voltage and frequency (or even DC instead of AC). Gradually producers merged, governments set standards, and market pressure ...

12

It may be a splicebox for optical fiber. Many power lines carry fiber inside one of the wires for telemetry and control.

12

You should not use 'thermals' when grounding the SMAs. Those ground tabs should go straight onto the big unbroken ground plane. It won't even be harder to solder, the bulk of the SMA has to be heated up anyway, so there's no need for those three printed inductors in the ground of each SMA. If you look at the ripple on your S21 plot, the repeating ripple is ...

12

They are earth wires so that lightning hits these before the main AC wires: - Picture source

11

The idea is that signals propagate at a finite speed, that is to say a certain signal takes t time to get from one end of the transmission line to the other line. The cable also has some intrinsic capacitance/inductance per unit length, which can be approximated with a characteristic impedance (assuming loss-less): Z_0 = \sqrt{\frac{L}{C}} \...

11

This is the same concept as behind twisted pair wires. Two wires running parallel will couple differently to the environment because they are on different sides. By twisting them, you average out the external coupling to be about the same from each wire to the environment. It's a little more complicated when you have 3 wires because you also want to ...

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