# Tag Info

42

Explanation So, the speed of light has (practically) nothing to do with it, you're right. WiFi chooses a transmission mode based on the quality of the link between two stations. The worse the link, the more robust the transmission needs to be. One way to get worse is to have a longer link, which means that less signal energy reaches the receiving end, ...

34

Dark fiber (unused fiberoptic cables) is a confusing term for me. Why would any company build so much excess capacity? The marginal cost of adding one more fiber when digging up a street is very, very small relative to the cost of digging up the street in the first place. So when you decide to dig a trench across the country, string a fiber across the ...

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 ...

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

Yes, it's called ground, and it's not always a perfect reference. For example, ground loops may occur, wherein different devices see slightly different ground voltages--this can arise due to voltage drops resulting from ground currents, or directly from induced voltages in loops due to changing electromagnetic fields. Not all devices use ground in the same ...

11

The application that you describe does not make sense to jump right into a custom silicon solution. The data rates that you anticipate can be easily handled by moderately priced FPGA technology and the FPGA can be programmed to implement the special protocol if your really believe that such protocol is needed. Much more often you should be considering a ...

11

The actual question is, why to design a protocol when everything already exists. For Ethenet solutions you take 10/100 and not 1GbE because it's still a little cheaper and much easier to layout. By the way, Ethernet can work without magnetics. But it does require MAC, which can be extra IC. Or do you have one in a microcontroller? 20Mbps is something ...

10

To elaborate on @Majenko's answer, both SGMII and 1000Base-x are dual 1000Mbps SERDES pairs (one in each direction), at least until the 1000Base-X signals reach the optical transceiver. The main difference is in the auto-negotiation capabilities. In 1000Base-X, auto-negotiation is limited to flow-control (and duplex, which is not really used since it's ...

10

Generally the Power is nothing but the product of current and voltage You are right ! You just have to calculate the voltage across the current source, and the current in the voltage source, multiply the related current and voltage, and you'll get the answers. for the current source : the voltage is 12V (the same of the voltage source, because they are in ...

10

I'd suggest the simplest route with the best likelihood of success and least software overhead would be to implement a 100Mbps Ethernet connection. You can implement this without any magnetics involved when the distances are small. Here's a start with information on the Intel 8255 PCI-Ethernet controller, and an application note on connections without ...

9

To get a good understanding of all that goes on here, you really need to draw. Maybe some issues might be clearer just by the picture: simulate this circuit – Schematic created using CircuitLab To handle the last one first: In this case, you are just increasing the load to the capacitor, so that's not very useful in most cases (there are exceptions, ...

8

Personally I wouldn't go for either RS422 or 1-wire. RS422 is really a point-to-point connection, like RS232 (and is usually used to extend RS232), and 1-wire is really only for local connections within a PCB. Instead you should use RS485. RS485 is like RS422 (RS232 with differential signalling), except it's designed to be point-to-multipoint, or fully ...

8

Most Ethernet systems are made up of a number of building blocks. The two most important are the Ethernet MAC Device (the device that actually makes and receives Ethernet frames), and the Ethernet PHY (PHYsical interface) device - the device that connects you to your wires, fibre, etc. These two devices are connected using a Media Independent Interface (...

7

Let's make some back-of-the envelope calculations: You have 2000 devices. If you're using 5 GHz WiFi, you'll have around 45 available non-overlapping channels for the US, a bit less in the EU, if you're using just 20 MHz per channel. This is of course, assuming you have equipment which properly supports dynamic frequency selection, and this might be an ...

7

This sounds like a perfect match for LoRa. 10km in rural areas, no additional licence required, and lots of example designs to learn from.

6

It appears that things are a bit more complicated than your quote from Wikipedia explains. The Wikipedia article doesn't appear to be entirely wrong, but it doesn't really explain things well either, as much as I hate to say this. The long story short: No, there will not be a distinguishable increase in voltage with signal reflections as far as the ...

6

For the input impedance, expand the matrix equation and then use the output condition: $Z_L=-\large \frac{V_2}{I_2}$ Similar approach for the output impedance.

6

Would using a typical high frequency audio amplifier that is connected to a satellite antenna boost the signal? No, absolutely not. In fact it would make things worse. An audio amplifier has absolutely no capability at the (near/-) microwave frequencies used by GSM. Quite likely it will function as a very effective attenuator and block almost all of the ...

6

This circuit basically operates as a switch, allowing current to flow through $Q_1$ depending on the state of $Q_2$. I assume that you have some logic driving the gate of the mosfet $Q_2$, by either pulling it to ground (turning it off), or pulling it high via resistor $R_1$. If the gate of $Q_2$ is high, it is ON, meaning that the gate of $Q_1$...

6

In addition to the previous answer just a comment on terminology, If industry speaks about Dark Fibre, especially renting them, this typically means you buy the fibre capacity and have to take yourself care for transmitting/receiving and multiplexing. It does not mean the Connection is not used or in excess, it means you are not bound to the provider ...

6

This is the well known capacitor paradox. The normal conventions of circuit theory break when you close the switch, because you have two different voltages in parallel and neither of them can change instantaneously. To use normal circuit analysis techniques you will need to introduce some additional assumptions or circuit elements that are not shown in the ...

5

Use switch RS485 has a bus topology. The big problem is that if you have star topology, every ray of the star has to be terminated. This way, the master transmitter will be loaded with 16x||120Ω = 7.5Ω. Of course such small impedance will overload the transmitter. There is another solution however. You should use a switch and connect the master only to the ...

5

You are confusing several things a) A resistor, a physical passive element that absorbs power b) A resistance, the mathematical ratio of voltage to current, that can be written for real resistors and for any situation where a voltage and current can be defined c) An abstract ideal model containing elements that can supply power, like current sources, ...

5

@AndrejaKo explained very well why using a WiFi infrastructure for this many devices is problematic. I'd go one step further and say: It's wrong for your application. Your application is time-critical navigation/control/process automation. WiFi is a Collision-avoiding multiple user scheme that makes absolutely zero guarantees about whether a single station ...

5

Beacon and sensor are terms used in short range networks used for position or presence location systems. BLE - Blue Tooth Low Power - systems are frequently used for this purpose as they interface with Bluetooth systems present in most "smart phones" and the low power consumption of BLE allows long battery life as nodes. The following is BLE focused as this ...

5

I suggest that you first learn a bit more about wireless communications Your question is like asking the difference between a concrete road and yellow cars. Both are needed to transport things and are not related but you cannot compare them directly. A frequency band and a IEEE standard are related but different things. That ISM band tells which ...

5

GSM by itself does not support data, just voice (even SMS is put ontop of GSM). Data service, beyond the 9600baud CSD (which doesn't seem to be supported by most phones/mobile providers anymore) requires the availability of GPRS or EDGE. Although both systems are very old, depending on where you are, there are still base stations around that only support GSM ...

5

The answers here are technical, i give a requirements engineering perspective: My view on it is simple You need at least 20Mbps to make it work, so dont specify 20 but "20 or more" for the application. any faster hardware also fulfills your requirement if the faster HW is cheaper/easier to develop because of existing standards, then your requirement can be ...

5

Can I connect the phone line to the coaxial cable, and plug in my modem at the other end? The conservative answer has to be "no" - phone lines are "balanced" in that the impedance presented by each wire to ground is constant. Coax cable is "unbalanced" and the impedance presented by the screen can be vastly different to the impedance presented to ground ...

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