It is a signal used to represent the data as discrete values

Digital signal use multi variables only rarely and also in order to send the computer information to transmission channels only analog signals are used.

Dear Sundara Siva Kumar v I want to sent "101001" from transmitter to receiver through air as medium between (both receiver and transmitter). According to you I need to convert these 101001 into analog signal and then transmit. otherwise 101001 can't transmit directly through air to receiver.

Thanks

Why not? Navigation Lighthouse is simple realization of digital wireless (optical) communication.

If you send digital data directly through the air you will probably interfering with other transmitter so to separate different channel the signal is modulated in a given frequency band. Obviously you can do this by digital modulation but due to harmonics you will impact other channel (modulation with a square signal has lots of harmonics) and during you demodulation depending on the other channel your signal will be distorted. Moreover you can suffer of bandwidth problem of your power amplifier which will distorted also your transmission.

To answer the question of lighthouse modulation, the light emission is kind of "analog" modulation for example a yellow light at 600nm correspond to a modulation at 500THz. Moreover walls isolate from neighbors at this frequency range so you can do what you want.

Hi Muhammad Abdul ,

I feel that you might think along the line: "For transmission by wire, we can just define, for example, V < 0.8 V = logical 0, V > 2.0 V = logical 1. So with wireless transmission, we could do the same for the strength of the radiation field at the position of the receiver, e.g. E < 0.8 V/m = logical 0, E > 2.0 V/m = logical 1."

At least three physical problems arise:

First, while the attenuation on short wires can be neglected, (unfocused) radiation decreases according to 1/r, r being the distance between transmitter and receiver. This could be overcome by an adaptive receiver.

Second and worse, the strength of the radiation depends on d I / d t, I being the electrical current in the antenna of the transmitter. So, the current in the antenna equals the integral of E over time, and therefore the number of consecutive logical 1s is limited by the maximum current the transmitter can cause in the antenna. As a consequence, you had to replace the original data by a code with a limited number of consecutive 1s.

Third, since the radiation depends on d I / d t, radiation cannot contain a DC component (in contrast to voltage and current on wires). So, the definition had to change to, e.g., E < -0.8 V/m = logical 0 and E > +0.8 V/m = logical 1, and again you had to replace the original data by a code with equal numbers of 0s and 1s. (O.k., your example 101001 would work but usually one would want to send any sequence of 0s and 1s, and on wire, you can indeed if you somehow solve the problem of synchronization.) And, worst of all, you could hardly distinguish between E < 0 and E > 0 if the radiation is reflected.

Additionally, there is the (organizational) problem of bandwidth, as Eric Feltrin already wrote.

I have to have FUN with this question. However, I must inform you that digital signals, ON / OFF keying are sent around the world ever day. I just sent one to Europe last night and discussed many topics with the guy on the other end of the link. It's called Morse Code and the information bandwidth was quite suitable to operate at power levels as low as a few watts. FUN! And I interference was minimal!

Obviously, you probably want to frame your question differently.

Alan Victor , I'm sure you modulated an RF carrier by your Morse key, and I wouldn't call that "directly". ;-)

I send fast code... Very fast.

Muhammad Abdul

The 'classical' fields of physics (electrical, gravitational, etc.) are continuously valued - and because that is true, one can perform differential algebra, giving rise to the wave equation (which requires that the field can have second order differentials)

Every transfer of information by those fields (and there are others, but we'll not discuss them) requires a perturbation in that field which is inherently analogue in nature - it has to be continuously differntiable otherwise a wave will not propagate.

The most important things have been said but to make things a bit more complicated ;-) here are some afterthoughts, and an attempt to answer the question: "What could be the 'most direct' way of wirelessly transmitting 0s and 1s?"

As to "analog" vs "digital": Certainly, we cannot transmit a signal with instantaneous transitions between two well separated states. But this is also true for wire-bound signals, in electronics mostly due to the need to charge or discharge something by a finite current. So, we cannot even try to transmit a "true" digital signal because we cannot generate one.

The bandwidth problem: While spark transmitters (which generated a wide spectrum) were banned about 1920, within the last two decades or so, short range ultra-wideband (UWB) communication is employed, for example on board of ships because it offers better performance in multi-reflection environments. I seem to remember from a book on UWB by Hans G. Schantz that Gauss shaped pulses have a "well behaved" UWB spectrum, and, with a suitable protocol, do not even interfere with narrow-band communication (and UWB communication is permitted and regulated by the FCC). So, if the edges of the "binary" signal had the shape of an "error function" (integral of a Gauss pulse) we might not even become outlaws. :-)

The most direct way of transmission: Control the current IT through one of Harmuth's "large current radiators" according to the information to be send. Place the receiver somewhere in front of the radiator. Because there is a differentiator inherently involved in the generation of radiation fields, the received signal has to be integrated in order to restore it to the original signal. In the attached sketch, it's still inverted but this can be easily mended, e.g. by turning the receiving antenna about 180°. Oops, "UR" should read "VR" in the English speaking part of the world; it's the output voltage of the receiving antenna. (Instead of a "real" integrator, a flip-flop with suitable signal shaping before its inputs will do the job.)

Basically, because digital signals are not actually exist in reality. All signals are analog.

When we decide that a voltage above a certain threshold is a "1", a voltage below a certain threshold is a "0", and the space in between is "undefined", then we interpret an analog signal as a digital value.

First of all, it is theoretically possible to transmit digital signals directly. Unfortunately when we use capacitors and inductors (energy storage devices) to match the impedance from the transmitter to the air (low impedance transistor say 5 ohms to 388 ohms (air)) these components introduce a bandwidth limiting match.

Since all impulse functions have infinite bandwidth (transmitting a 1 and a zero) the bandwidth of the transceiver must be multi octave in order to have any reasonable efficiency.

Systems engineers simplify the problem by introducing direct sequence modulation where a carrier is modulated 0/180 degrees dependent on the data rate.

If you really want to build a direct transmitter, I have some ideas. Contact me at [email protected]

Jim