# Tag Info

34

But how come unbalancedness of coaxial cables have no problem in impedance balancing issues? The beautiful thing about coax is that the shield shunts mostly all external electric field interference to ground and the inner wire is largely unaffected. For an external magnetic field interference, a subtle thing happens; the current that flows in the shield ...

25

As with any radio receiver, if it can handle a higher data rate, then it is usually burdened with having a higher RF bandwidth and this inevitably means more received background noise i.e. a wider BW lets in more noise and hence, you need a higher received signal level to operate with a decent SNR (signal to noise ratio). Therefore WiFi is at a significant ...

23

the Titanic communicated with Canada, 400 miles away, with relatively low-powered equipment Quote from this website: - The Titanic's "wireless" equipment was the most powerful in use at the time. The main transmitter was a rotary spark design, powered by a 5 kW motor alternator, fed from the ship's lighting circuit. The equipment operated into ...

14

Andy talks about how coax works in general, but another point is that video generally doesn't have the same SNR requirements as audio to begin with. Data with 8 to 10 bits per color channel provides very good pictures, and this represents an SNR of only 50 to 60 dB. On the other hand, to be considered "CD quality", audio must have at least 16 bits of ...

10

The main technical difference is how they reject interference. Twisted pair relies on the interference affecting both wires equally, generating common mode noise that is easily rejected by the differential receiver. This works well for magnetic interference down to very low frequencies. Coax cable relies on the magnetic interference inducing opposing ...

9

As PlasmaHH says, it doesn't boost the total power - it can't, it's a passive device. Instead it makes the antenna much more directional. Signal behind or to the side will be much weaker. Usually you'll use them in pairs to make a link between two buildings. Very similar principles to the directional reflectors in flashlights or car headlights.

8

in addition to Andy's answers, WIFI is usually limited in power, 30dBm in north America, lower levels in most of the world. LTE usually can transmit up to 4W (36dBm) And the towers transmit at a much higher power. Also, LTE has much better network management capabilities (automatically finding the best channel and data rate), the towers have much better ...

8

A completely separate reason that coax is favored for TV is frequency response. The losses associated with twisted pair rise rapidly with frequency, to the point where DSL modems struggle to use even the lowest 10 MHz of bandwidth on analog phone subscriber loops. For the same reason, high-speed Ethernet (1G, 10G and up) over twisted pair is limited to very ...

7

To avoid the possible number of obstacles between the phones and the cell tower. And height position point is often in sight (or almost) from many ground-level points. Obstacles cause reflections, scattering and absorption effects that compromise the S/N ratio.

7

Funnily enough if you search "Certain Factors Affecting Telegraph Speed." in the usual online sources, you will find the original text by Nyquist. It includes a table: Number of current values employed Relative amount of intelligence ... transmitted 2 100 3 158 4 ...

6

I can't find the values of C12, C14, C19 and C20 capacitors in the bill of materials. These should be somehow calculated or what? This is the question I'm least sure about. Maybe these are intended to be not loaded. This would be the case if they determined they only needed a low-pass filter instead of a band-pass filter after designing and testing the ...

6

From http://hf.ro/ : The Titanic's "wireless" equipment was the most powerful in use at the time. The main transmitter was a rotary spark design, powered by a 5 kW motor alternator, fed from the ship's lighting circuit A spark gap transmitter is the simplest possible form of radio transmitter, modulated with on-off keying (morse code). Even allowing for ...

6

It's a standard Philips PM5544 test pattern generator image. Used by many TV stations all over the world. It could be considered part of pop culture too due to this.

6

The high-speed channel C can transmit two bits in the same time that X and A each produce one bit, so it can simply transmit both bits, one after the other. No bits get lost. Actually, in the PSTN, samples (bytes), rather than bits, are interleaved. In this way, a 1.544 Mbps T1 line can handle 24 conversations simultaneously. 8000 times a second, a complete ...

6

How is transmission line impedance selected? explains why transmission line impedance matters. The CATV industry deals with low-level signals, so it cares ONLY about loss and not at all about power-handling. That's why they chose 75Ω transmission lines.

5

No and Yes. First the no bit. The GSM cellular network is designed around communication between a handset and a base station. The base station does all of the control here. Firstly it decides who can talk when (see multiple access, TDMA, CDMA, etc.) in order to allow many phones to connect. Secondly, it decides how to route a call - you call up a number on ...

5

As the other answer states, at a lower position, you start to have more issues with reflection, scattering and absorption. In other words, at a lower position, interference from obstacles are more likely to happen, and negatively affect the range. You also ask: Does height increases antenna gain because it may provide directionality? No, gain is ...

4

Power spectrum density at MW frequencies is very poor at a point it is unable to penetrate obstacle without loosing a lot of power. That's not what power spectral density means. PSD is just a measure of power at a given frequency. But you're right that microwaves don't pass through objects as well as longer wavelengths do (in most cases; there are ...

4

LTE (and GSM I believe) uses OFDM (orthogonal frequency division multiplexing) and simulataneously transmits several different "carriers" each containing a fraction of the full data bits. Upon reception, these demodulated fractions are then combined to restore the original (and full) data. This means that each "carrier" is detectable in its own right. ...

4

As mentioned by Barry, this has got to do with beamforming. If you consider what occurs when a signal hits the two antennas, as shown in the following figure: The signal received by the antennas will have a time delay between the antennas. This time delay is related to the angle theta that the signal is arriving from. When adding the signals together at ...

4

Your antenna supplier is probably also an U-blox reseller ;) Seriously - pretty much all cellular modules: Telit, U-blox, Gemalto [former Cinterion], Simcom, Quectel are basically the same (I've tried Telit, U-blox, Simcom and Quectel myself). The basic AT commands (like dial, send SMS etc.) are standarized by 3GPP, and are the same across all modules. ...

4

These are just rough labels that depend on context. Obviously, a narrowband signal has a narrower bandwidth than a wideband signal in the same context, but that's about all you can tell from that. This is no different than "big" and "small" in everyday language. Saying something is big or small without context is meaningless. A small house, for example, ...

4

In the RF world one way to specify noise is as $dBm/Hz$ and where dBm is $10*log_{10}(milliwatts)$ this gives you a way to compare noise between systems with different bandwidths, just divide your noise power by the system's bandwidth. E.g. Say I want to receive a 0dBm signal with a system that has a bandwidth of 1Hz and a noise power density on the ...

4

At least as I read it, he states the misconception fairly clearly: the sound produced at one end of a circuit actually travels over that circuit, in order to be heard at the other end. His point is that the sound at one end of the circuit is converted to electrical signals by the microphone, then that resulting electricity travels through the circuit, ...

4

I think the clue might be in "published in 1905". The electric telephone was radically different to the speaking tube which was popular in the previous century (and still has applications now). Figure 1. A 19th century speaking tube. Science Photo. The article is merely pointing out that there is an acoustic-electric interface at the microphone and an ...

3

Any impedance "bumps" in the circuit will have "some" affect on achievable data rate, but as long as a switch is a sensible one and the connections are competent and the pairs are kept as undisturbed as possible, I'd expect no significant impact. Keep twisted pairs twisted for as much of their length as is sensibly possible - no need to overdo it. ie Avoid ...

3

It will be possible. But it is not yet. D2D is in 3GPP Release 12, under Proximity Services (ProSe).

3

It all depends on your frequency standard. 3Hz in 1.2GHz is not possible for cheap 10MHz standards, TCXOs even, but with a decent DOCXO or rubidium standard, it will be straightforward. The trick is not to try to count the frequency offset, but to compare your received phase with a reference. For a 3Hz difference, the comparison will spin a whole 3 times ...

3

Even as far back as the early 1900s, telegrams transmitted wirelessly could reach hundreds of miles. For instance, the Titanic communicated with Canada, 400 miles away, with relatively low-powered equipment. Given that telegraphs are very simple, how could these pulses travel so far? Besides the fact, as others have pointed out, that the power really wasn't ...

3

Given that telegraphs are very simple, how could these pulses travel so far? By using sufficient power and containing frequencies that supported a propagation that could go around the earth's curvature that distance. And would these pulses still travel that far today with the same equipment? Yes. It is known as HF (high frequency) radio. For over ...

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