# Tag Info

13

What you show is a crude reflector. Yes, you can use reflectors around a antenna to get more power in a particular direction at the expense of other directions. This can be useful when the other antenna is in a known direction. However, there are several problems with this: It may violate the law. You don't give your location (remember that filling in ...

8

This is engineering. Test it. It's not like it takes a lot of money or time to do experimentally. As far as what the theory says, it will always have a slight effect. The magnitude of this effect depends on the nature of the location, the door, and the wall. More metallic/heavy objects block the signal, so if it's a weak signal and a bad environment, it ...

7

With a sample rate of 250 Hz, you could easily send 100 bits/second or more. In 0.5 second, that would be on the order of 50-60 bits. The question is, what bit patterns should you select that are readily distinguishable from each other and also from outside noise and interference? A common solution is to use pseudorandom bit sequences, also known as Barker ...

6

I think the diverse range of names for the second argument arises from the fact that the convolution operation is so useful in so many different fields. It is helpful to recall what the convolution operation does before addressing the specific terms. Quoting from Wolfram Mathworld, "a convolution is an integral that expresses the amount of overlap of one ...

4

The smallest feature that you need to capture is the dip between 3.5 and 4. If you use a sampling period which is greater than 0.5, then you may end up not capturing this feature. The sampling period must therefore be $T\leq 0.5$ in order not to lose any features of the signal.

4

"Window" is often used to mean a successive set of samples processed as a batch. In this case it appears that the algorithm works on batches of 500 samples at a time.

3

Alhtough this answer should be awarded to Pete, because he has spotted it first. The accelerometer has a sensitivity of 5%, which corresponds to 100[mV/g]. what you are measuring is 0.1[m/s^2], which is about 0.01g. So the actual signal you should be receiving from the piezoelectric accelerometer is about 1[mV], which is quite low. Now, if you see the ...

3

This might work to boost the signal in one direction, but it will reduce it in other directions. Antennas are often built with elements (like your drink can) that couple to the primary radiator. These act as "Directors" or "Reflectors". You see directors on a classic TV antenna - All the cross beams along the main beam of the antenna. You see reflectors on ...

3

The term time-window or often just window is used to mean a short period of time during which something is possible, or during which you observe something, or during which you look for something. Note that the paper introduces this concept earlier on when it says For that, the recorded EMG-data were rectified and smoothed with a root mean square (RMS) ...

3

First, you should link in a reference to the Hata and Ericsson models. I haven't heard of them, and a quick search on Google didn't give anything. Path loss and received signal strength are typically calculated using the Friis Transmission Equation. http://en.wikipedia.org/wiki/Friis_transmission_equation To use this equation you must know the distance ...

2

First point is that signum is not continuous with the jump at $t=0$. Second because of the absolute value in the integral it has the same $E$ and $P$ as a constant signal $1$. This means that $E_{sgn}=+\infty$ and $P_{sgn}=1$

2

All of these cans are made up of Aluminum. Aluminum is a good conductive material and a dense material. More dense material means more capability of conductance. They can be used as antennas to transmit the signals but I am not sure whether this thing improves the WiFi signal strength as I had not tested it by myself. But one thing that makes sense to me is ...

2

To prevent loss of signal you need to sample at twice the highest frequency presented in the signal. This is also known as Nyquist rate. Assuming that time t is in seconds, the smallest time period is about 0.5s or the highest time frequency is 2Hz. So if sampled between 2Hz and 4Hz the processed signal will be subjected to what is known as aliasing. If ...

2

I live in a big old 1920s built house. The bedroom is one floor above the router, and one room adjacent. The floors in my house are wooden, the walls are stone, the cielings are high and the doors are solid wood. If I try to stream video on Chromecast in my bedroom with the bedroom door closed, it intermittently buffers. Chromecast even grumbled that the ...

1

There's a "rule of thumb" for any phase-sensitive control loop that the processing phase lag has to be less than $\frac{\pi}{4}$ at the frequencies of interest to be stable. For decent noise-cancelling, you'll want to do considerably better than that. I suspect you can find the actual time lag (not phase) for a given product by looking at the ...

1

You can use the following formula to produce the white noise for one cell. = 0.5*NORM.S.INV(RAND()) Where: 0.5 : can change to any non-zero number. It will control the range of the data. NORM.S.INV(RAND()) : produces a random number from -inf to inf, with mean zero and standard deviation 1 you can create a column for noise with this equation, and then just ...

1

Unless the room noise is loud enough to cause physical vibrations in the playback head, leading to misalignment of the head vs. tape track (which could cause crosstalk or amplitude dropoff), there's no way that an acoustic signal can affect the flow of electrons in a wire. BTW, it is true that some LPs show "print-thru," a situation where the ...

1

You are using a piezo electric accelerometer. There are always always always offsets and low frequency noise on a piezoelectric accel. Depending on the charge amp, anything below about 3 hz is meaningless. Just high pass filter the signal to get rid of it. If you need to read below 3 hz then you shouldn't use a piezoelectric. Use mems or piezo resistive in ...

1

The stereotypical tinfoil hat (or the equivalent) would allow you to create a faraday cage, preventing the signals being sent/received. Of course, it would have to have been done prior to turning it on, or in this case, plugging it in. Why Does Aluminum Foil Block Cell Phone Signals?

1

If your objective is only to determine device in range, and you've located a suitable wireless camera to meet your size requirements, such a device could be used without privacy concerns if you painted over the lens. You could also simply place the camera in a completely solid enclosure. Your receiver would change from a no-signal status to a black/blank ...

1

Your equation is correct for your definition of $d$. However, your definition of $d$ seems incorrect. $d$ is supposed to the be distance between the transmitter and the receiver, that is the distance on a straight line from the transmitter to the receiver. In your diagram you have (I think incorrectly) defined $d$ as the horizontal distance on some plane, ...

1

The wavy symbols are integrators, which means that: $$\frac{dy}{dt} = x_1$$ $$\frac{dx_1}{dt} = x_2$$ Then the "+" sign gives you (the triangles are "gains", which means multiply): $$x_2 = x(t) - a_0 y(t) - a_1 x_1$$ If you combine all this together, you get your differential equation(s).

1

First, I'm assuming that by "moving window", you mean breaking the signal up into smaller chunks and filtering each chunk separately. In the signal processing word, "moving window" would often mean an FIR filter (e.g. fir1() in matlab), but because you explicitly said you are using butterworth filter, which is an IIR filter, I assume that is not what you ...

1

The problem that you describe comes from the fact that you calculating the average of the vector with numerical values. In order to calculate the exact mean of $\sin(x)$ or other functions, you should use computer algebra systems like (MATLAB symolic toolbox which is not always exact, Mupad in MATLAB, Maple, Mathematica, sympy package for Python). Another ...

1

A linear operator $\Theta$ is an operator acting on functions $F$ and $G$, with coefficients $a$ and $b$, such that the following equality holds: $$\Theta(aF+bG) = a \Theta(F) + b \Theta(G)$$ Put into words, order of operations does not matter with respect to the linear operator, multiplication of functions by coefficients, and addition of functions with ...

1

It is too small a surface area to be an effective microwave reflector. The shape is wrong too, it must be parabolic with respect to the transmitting fractal antenna of the router. Yours is perpendicular to it. http://www.instructables.com/id/Easy-to-Build-WIFI-24GHz-Yagi-Antenna/ With the advent of embedded fractal antennas, we no longer need external ...

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