What is it?

kv4p HT is a homebrew Open Source VHF radio that can turn your android mobile phone capable of voice and text communication completely off-grid. At least a Technician class amateur radio license.

The radio simply plugs into the USB C port on your Android smartphone and transforms it into a fully-fledged handheld radio transceiver. It’s completely open source (GPL3): the Android app, ESP32 firmware, PCB designs, and 3D printer files.

kv4p HT project official website is https://kv4p.com/

To buy full kit shown in the image : ($38) This is the link 1

Another link for the kit : ($59) This is the link 2

(We are not affiliated with any kit vendors listed here).

It’s small enough to fit in your pocket and take anywhere, and since it has no internal battery it’s the perfect radio to put in a go-bag or your car’s glove compartment.

We will be installing a weather station in this area. You will be able to see local temperature, humidity, wind direction and wind speed.

Electricity is a difficult substance to appreciate with the human senses. About the only way you get a feeling for it is to moisten the tongue and apply it between the terminals of a 9 volt battery. Of course, you get more idea if you are unfortunate enough or foolish enough to touch a live mains cable… providing that you survive to describe the experience.

Here are some electrical quantities and their SI units and symbols.

• Electric charge (coulombs), q or Q
• Volume charge density (coulombs per cubic meter) rho
• Surface charge density (coulombs per square meter) sigma
• Linear charge density (coulombs per meter) lambda
• Electrostatic potential (volts) phi
• Electric field (volts per meter) E
• Electric induction D = epsilon.E (coulombs per square meter) D
• Electric current (amps or coulombs per second) I
• Electric current density (amps per square meter) J
• Magnetic field H (amps per meter or amp turns per meter) H
• Magnetic field B = mu.H (tesla) B
• Magnetic vector potential (tesla meters) A
• Capacitance (coulombs per volt, or Farads) C
• Inductance (volts-seconds per amp, or Henries) L
• Permittivity (Farads per meter) epsilon
• Permeability (Henries per meter) mu
• Velocity of light in vacuum (meters per second) c

A loose description.

Electric fields form lines which are trajectories along which a very small free charge would travel in the absence of a magnetic field in the same place.

Magnetic fields form lines along which little bar magnets “dipoles” or iron filings would align.

The flow of charge constitutes a current. Charge is neither created or destroyed, so if in a region there is a changing charge (with time) then there must be current flow in or out of that region. Currents often travel along electric field line directions and generate magnetic fields.

In regions of constant charge density, all currents flow in closed loops. If the current loop does not close then there must be accumulation of charge which varies with time.

All magnetic fields B form closed loops. Loops of B are linked with loops of current density (J) or displacement current density ((d/dt)D).

Electric field lines either begin or end on charges or else they too form closed loops.

In a radiating situation, the currents, charges, fields, and potentials are all time varying. If one assumes a sinusoidal variation with time having angular frequency omega, then a general radiation problem can be solved by Fourier superposition of the solutions at different values of the angular frequency omega. Fortunately in most practical situations the fractional bandwidth occupied by the signal is rather small and so the properties of the radiating structure do not vary very much across the band of signal frequencies.

Mathematical presentation of Maxwell’s Equations

There are four of Maxwell’s Equations plus a charge continuity equation. You need to study your favorite vector differential calculus book to learn about the divergence (div), curl (curl), and gradient (grad). Roughly, the gradient represents the “slope” of a scalar field along the direction of maximum change, and the gradient is a vector. The divergence represents the flow out of a small volume, per unit volume, and is a scalar. The curl represents the rotation of a field around a point; for a magnetic field forming closed loops it is the limit of the size of the field times the perimeter of the loop divided by the area of the loop, as the loop shrinks to nothing. The curl is a vector as it has an associated axis of circulation or direction in space.

Here are the four Maxwell’s equations and the continuity equation.

• div D = rho
• div B = 0
• curl E = – (d/dt)B
• curl H = (d/dt)D + J
  and the continuity equation for charge….
• div J + (d/dt)rho = 0

Let us go through these…

• Lines of D, electric induction, are proportional to the electric field and “diverge” away from a region containing charge density rho. If there is a surface charge sigma (coulombs per square meter) then close to the charge sheet is an electric induction field D = sigma.
• Lines of B never diverge from anything, and form closed loops.
• Electric field lines which form closed loops, encircle a changing magnetic field. Lenz’s law applies; the electric field if it drove a current would do so in such a way as to reduce the changing magnetic field within the loop. Electric field lines which do not form closed loops begin and end on charge, as we have seen from the first equation.
• Magnetic field lines H form loops which encircle both conduction current density J, and also “displacement current density” (d/dt)D which is generated by time-varying electric fields. Maxwell’s great achievement was to realize that the term in (d/dt)D was necessary; if you consider a capacitor with plates very close together, then if the displacement current term did not generate magnetic field loops there would be an unphysical discontinuity in the magnetic fields around the capacitor plates as you passed alternating current through the capacitor.
• The current density J flowing out of a region (“diverging”) must result in a decrease of charge within the region.

Sources of fields

Currents and charges give rise to the fields and are called “sources”. More directly, the potentials can be calculated from the source charge and current distributions and the fields are then derived from the potentials.

In an electrostatics situation the electric field E is given just by

E = -grad(phi) which begins and ends on charges.

However, if there are changing magnetic fields there is an additional contribution to the electric field forming the closed loops which circulate around the changing magnetic field lines.

The magnetic vector potential A may be used to find the magnetic field B by the relation (which is a definition of A)

B = curl(A)

To define A completely we have to specify its divergence as well as its curl, and possibly an additive constant also. If we do this according to what is known as the “Lorentz Gauge” then the electric field may be calculated from

E = -(d/dt)A – grad(phi)

Part of the source of electric field is from the magnetic vector potential A and part from the scalar potential phi.

If we know the potentials A and phi completely for all time and space we can calculate the fields E and B.

A little more detailed mathematics (see the text of your choice) shows that the conduction currents J give rise to the magnetic vector potential A, and the source charges rho give rise to the scalar potential phi. Because there is a maximum velocity of propagation c=3E8 meters per second, the potentials A and phi at a distance r meters from the source cannot follow changes in the source distributions until a time r/c seconds later. These potentials are known as the “retarded potentials”.

Considering the equation

E = -grad(phi) – (d/dt)A

we observe that in the far field the potentials A and phi fall off as 1/r where r is the distance from the sources. However, applying the gradient operator to phi puts in a further dependence of 1/r to the contribution -grad(phi). Thus the electric field E due to the charges in the source falls off as 1/(r^2) and can be neglected at large r compared to the electric field contribution -(d/dt)A which falls off as 1/r.

Thus, for far field calculations it is true to say that only the source currents on the antenna structure need be considered.

For time-harmonic currents, since the charge continuity equation links the current density J to the source charge density rho, the potential phi may be expressed in terms of the vector potential A, and so there is no loss of generality in considering the far-fields as being entirely due to source currents plus any pre-existing electromagnetic propagating waves.

It is very easy to conduct a gedankenexperiment to show that, for near field scenarios, the conduction currents on the source structures are not sufficient to use as a basis for field calculations.

Consider an open ended waveguide carrying a TE10 waveguide mode. Let us assume that the waveguide is very large in transverse dimensions compared to a wavelength. Now consider a point on the axis of the waveguide, beyond the plane at which the waveguide stops, along the z-direction. Let us assume that this point is closer to the point z=0 which defines the exit plane, than it is to any of the current elements on the waveguide walls. If only conduction currents starting at time zero contribute to the field strength at this point, there can be no field at this observation point at a time less than the retardation time from the guide walls.

Now, as we let the guide dimensions get larger (without limit) we can show that for any specific point on the axis of the waveguide, beyond the waveguide end plane, the fields due to the currents in the walls are zero for finite time. If we take the view that the waveguide is the only structure generating em fields, and that there are no pre-existing propagating waves along the axis of the guide, then this result appears contradictory and unphysical, and so the accepted theory, and probably all the antenna calculations and simulation code based on fields being set up only by the source currents, may be in error.

Another way of looking at this problem is that the wave front progresses along the waveguide at the group velocity, which is lower than the velocity of light in the medium. Regarded as a radiating structure, the mouth of the waveguide sets off a propagating wave in free space which travels at the velocity of light. There must therefore be a contribution to the radiated fields from the center of the guide mouth, where the conduction currents are zero. Yet another insight may be obtained by appealing to Huygen’s principle in wave optics, where each point on a propagating wave front is regarded as giving rise to an outgoing hemispherical wave front. Thus if we consider radiation from a burst of microwaves propagating in free space at time zero, there are no source currents in the problem at all, within the limits of the definition of the problem.

Most antenna calculations are made assuming that the time harmonic radiation has persisted/persists for all times past and future and so the problem of what happens at the start of a radiating wave front is hidden from the analysis.

Further examination of the equations shows that A and therefore E (in the far field) lies in the preferred direction of the current sources. (The preferred direction may be taken to be an average direction over all the source currents.) The magnetic field B on the other hand forms loops around the current direction, and therefore B is at right angles to E and to the preferred direction of the current sources.

Moving charge constitutes a current. In most wires, there is a near-balance between mobile negative charge (electrons) and a background sea of positive charge (ions) which is stationary. It is therefore possible to have an “electrically neutral current” wherein the moving charge forming the current does not itself provide a source of charge density rho and therefore of electrostatic scalar potential phi.

For this reason, in many antennas textbooks, near field as well as far field radiation is assumed to be entirely determined if only the current distribution in the source is known. This is sufficient for many antennas problems. However, where there are serious discrepancies between the predictions of standard theory and the measurements on a specific antenna structure, one should look to see if there are any significant time-varying charge accumulations within the antenna conductor structure, or on any local scattering objects. One should also look to see if there are any photons emitted by transitions between electron energy levels, and to see if there are any pre-existing EM waves.

Antenna calculations

We are part way to our objective. If we know the current (and possibly charge) distributions on our antenna structure we should be able to calculate the fields anywhere for all time. However, in many antenna calculation scenarios the current distribution is not a “given” property of the problem. Often the antenna is connected to a length of transmission line (a feed), which may be coaxial cable, parallel wire line, microstrip, or it may be waveguide. The feed itself will have currents on it and may contribute to the radiation. Frequently one may assume a voltage at the junction between the feed and the antenna structure proper, but calculating the current and charge distribution on the structure after that point may be very difficult.

In aperture antenna radiation pattern calculations, a frequent ploy is to create a fictitious surface across the mouth of the aperture. Arguing backwards from the result, there will be electric and magnetic field lines intersecting this surface. One then can create an arrangement of fictitious charges and currents, and also magnetic charges and currents, on this surface. These are calculated to give rise to the local field structures on the surface, and then used to calculate the radiation field patterns at other points in space. Of course, this method requires one to have a reasonably accurate knowledge of the fields on the fictitious surface in the first place, and this may be no easier than calculating the current and charge distributions on the source structure.

Of course, if the fields are known accurately across a surface one can use Fourier Transform techniques to calculate the radiation patterns in the far field. Such techniques are frequently referred to as the “geometrical theory of diffraction”. If there are physical dielectric or magnetic obstacles in the near field then calculation of the perturbations of the field patterns by the objects may be necessary, such methods may be grouped under the heading “physical theory of diffraction”.

One of the difficulties with all antenna calculations on complex structures is that in most cases the measurement techniques available do not have sufficient precision and accuracy to determine the validity of the calculation method used. Thus many antenna calculations have to be regarded as speculative; this is a problem for the simulator particularly if the method used consumes large amounts of computing resources to little avail.

Diodes & Transistors

In the early days of electricity there were only two groups of material: insulators and conductors. Insulators are matters, which do not allow the flow of electric current through them. Glass, porcelain, dry air and dry wood are well known insulators. Metals are known to be good conductors, with copper and silver among the best. The conductivity of a particular material depends on the number of free electrons present in it.

There is another group of material known as semiconductors. Semiconductors like germanium and silicon are bad conductors of electricity in their purest form. But when certain impurities (indium or arsenic, which have a slightly different atomic structure from that of germanium or silicon) are added in the form of carefully controlled quantities, either an increase of free electrons or deficiency of electrons results. A semiconductor is called an n-type semiconductor where conduction takes place by reason of excess free electrons. A semiconductor is called a p-type semiconductor where conduction takes place due to freely moving ‘holes’ (positively charged) which replace electrons displaced by random electron movement in the material.

DIODES

When pieces of p-type and n-type semiconductors are joined together, a p-n junction results. Flow of electric current through such a junction is possible only when the positive pole of the battery (voltage source) is connected to the p-type semiconductor and the negative pole to the n-type semiconductor.

This is called the “forward biased” condition. In this condition, positively charged holes are repelled by the battery voltage towards the junction between p and n type material. Simultaneously, the electrons in the n-type material are repelled by the negative battery voltage toward the p-n junction. Despite the presence of a potential barrier at the p-n junction, which prevents electrons and holes from moving across and combining, under the influence of the electric field of the battery the holes move to the right across the junction

and the electrons move to the left. As a result, electrons and holes combine and for each combination of that takes place near the junction, a covalent bond near the positive battery terminal breaks down, an electron is liberated and enters the positive terminal. This action creates a new hole which moves to the right toward the p-n junction.

At the opposite end, in the N-region near the negative terminal, more electrons arrive from the negative battery terminal and enter the n-region to replace the electrons lost by combination with holes near the junction. These electrons move toward the junction at the left, where they again combine with new holes arriving there. As a consequence, a relatively large current flows through the junction. The current through the external connecting wires and battery is due to that of the flow of electrons.

If, however, the polarity of the battery is reversed, i.e., the positive terminal is connected to n-type semiconductor and the negative terminal of the battery to the p-type semiconductor, the p-n junction will block the electron flow by building up a voltage barrier at the junction. The holes are now attracted to the negative battery terminal and move away from the junction because of the attraction of the positive terminal. Since there are effectively no hole and electron carriers in the vicinity of the junction, current flow stops almost completely.

This type of device is called a “solid state diode” or a semiconductor. By exploiting their property of one way flow of electric current, they can be utilized to convert alternating current to direct current (known as rectification). Without adequate filtering, the resultant d.c. is pulsating in nature.

TRANSISTORSThe simplest of the transistors are of two types-either p-n-p or n-p-n. Two p-n junction diodes can be sandwiched back to back to form a p-n-p or n-p-n junction transistor. But in a practical transistor, the center or n-type portion of the sandwich is extremely thin in comparison to the p-regions. In the 1st illustration, both the p-n junctions are reverse biased.

In this type of connection, holes in the each of p-region are attracted towards the negative battery terminal and the mobile electrons in the n-region are initially moved away from both junctions in the direction of the positive battery terminal. Due to the displacement of holes and electrons, there will be no current flow in the external circuit.

In the 2nd illustration, one of the p-n junctions is forward biased, while the other is reversed biased. In a transistor, the middle layer (here n-region) is called the base, the forward biased p-n junction is called the emitter junction and the reverse biased p-n junction is called collector junction. Due to the positive potential at the emitter junction, the holes in the p-region cross into the n-region (the base). But this region is very thin and there are very few electrons with which holes can combine. So, majority of the holes drift across the base into the collector junction. About 5 per cent of them are lost in the base region as they combine with electrons.

For each hole that is lost by combination with an electron in the base and collector areas, a covalent bond near the emitter electrode breaks down and a liberated electron leaves the emitter electrode and enters the positive battery terminal. The new hole that is formed then moves immediately toward the emitter junction, and the process is repeated.

Thus, a continuous supply of holes are injected into the emitter junction, which flow across the base region and collector junction, where they are gathered up by the negative collector voltage. The flow of current within the p-n-p transistor thus takes place by hole conduction from emitter to collector, while conduction in the external circuit is due to the conduction of electrons.

Because of the reverse bias no current can flow in the collector circuit, unless current is introduced into the emitter. Since a small emitter voltage of about 0.1 to 0.5 volt permits the flow of an appreciable emitter current, the input power to the emitter circuit is quite small. As we have seen, the collector current due to the diffusion of holes is almost as large as the emitter current. Moreover, the collector voltage can be as high as 45 volts, thus permitting relatively large output powers.

A large amount of power in the collector circuit may be controlled by a small amount of power in the emitter circuit. The power gain in a transistor (power out/power in) thus may be quite high, reaching values in the order of 1000.

The ratio of collector current to emitter current is known as alpha (a) and it is the measure of possible current amplification in a transistor. a cannot be higher than 1.

Transistor Symbols and Connection:

When transistors are operated as amplifier, three different basic circuit connections are possible: (a) Common-base, emitter input; (b) common-emitter, base input; and (c) common-collector, base-input.

Regardless of the circuit connection the emitter is always forward biased and collector is always reverse biased.

There are some narrow band (field communication) wich only modulate the frequency 1-5kHz.There are some different way to bring out the sound from the RF-signal. I will explain a way by using a “quad coil”.A FM demodulator produces an output voltage that is proportional to the instantaneous frequency of the input.There are three general categories of FM demodulator circuit:Phase-locked loop (PLL) demodulatorSlope detection/FM discriminatorQuadrature detector

They all produce an output voltage proportional to the instantaneous input frequency.I will not explain the two first types, but I will explain more about the last one.

Quadrature FM detectors use a high-reactance capacitor (C2) to produce two signals with a 90 degree phase difference. The phase-shifted signal is then applied to an LC-tuned resonant at the carrier frequency (L1 and C3). Frequency changes will then produce an additional leading or lagging phase shift into the mixer.

Single Sideband Suppressed Carrier (SSB-SC):
Single Sideband Suppressed Carrier (SSB-SC) modulation was the basis for all long distance telephone communications up until the last decade. It was called “L carrier.” It consisted of groups of telephone conversations modulated on upper and/or lower sidebands of contiguous suppressed carriers. The groupings and sideband orientations (USB, LSB) supported hundreds and thousands of individual telephone conversations.
Due to the nature of-SSB, in order to properly recover the fidelity of the original audio, a pilot carrier was distributed to all locations (from a single very stable frequency source), such that, the phase relationship of the demodulated (product detection) audio to the original modulated audio was maintained.

Also, SSB was used by the U.S. Air force’s Strategic Air Command (SAC) to insure reliable communications between their nuclear bombers and NORAD. In fact, before satellite communications SSB-was the only reliable form of communications with the bombers.

The main reason-SSB-is superior to-AM,-and most other forms of modulation is due to the following:

SSB-ver-AM
(1) Since the carrier is not transmitted, there is a reduction by 50%
of the transmitted power (-3dBm). –In AM @100% modulation: 1/2 of the power is comprised of the carrier; with the remaining (1/2) power in both sidebands.

(2) Because in SSB, only one sideband is transmitted, there is a further reduction
by 50% in transmitted power (-3dBm (+) -3dBm = -6dBm).

(3) Finally, because only one sideband is received, the receiver’s needed
bandwidth is reduced by one half–thus effectively reducing the
required power by the transmitter another 50% (-3dBm (+) -3dBm (+) -3dBm = -9dBm). –Remember, if a receiver’s bandwidth can be reduced by 50%: the needed transmitter power is also reduced by 50%, i.e., the receiver’s Signal to Noise Ratio (SNR) is improved as the receiver bandwidth is reduced. This of course implies that the signal containing the information is not lost–which is the case in this instance. –Huh? Its true: if I’m Lying, I’m Dying!

Example: A HAM running 2000 Watts AM, would sound no better than another
HAM running 250 Watts PEP (Peak Envelop Power) on-SSB.

What is Single Side-band?

Before you can understand what SSB is, you must understand how audio is transmitted via radio waves. The method by which audio is impressed on a radio signal is called modulation. The two types of modulation that most people are familiar with are AM (amplitude modulation) and FM (frequency modulation), for which the AM and FM broadcast bands were named.

The Carrier.

In an AM-modulated radio signal, a base signal, called the carrier, is continuously broadcast. The two modulating signals are called the sidebands. Any audio that you hear on an AM broadcast station is from the two sidebands. When the radio station is not transmitting any sound, you can still hear that a signal is present; that is the carrier.

These two modulating (audio) sidebands are located on either side of the carrier signal–one just above the other just below. As a result, the sideband located just above the carrier frequency is called the upper sideband and that which is located just below the carrier frequency is called the lower sideband.

The Sidebands.

The pieces that fit together to form an AM broadcast signal are quite important. Although AM signals were transmitted almost exclusively for decades, it was discovered that the AM signal could be dissected. The first amateur radio operators to experiment with these processes often used both sidebands without the carrier. This is known as double sideband (DSB). DSB was typically used in the earlier operations because it was much easier to strip out just the carrier than to strip out the carrier and one of the sidebands.

Several years later (and still true today), it was much more common in the amateur bands to transmit merely using one of the sidebands, which is known as single sideband (SSB). Single sideband transmissions can consist of either the lower sideband (LSB) or the upper sideband (USB).

If you listen to an SSB signal on an AM modulation receiver, the voices are altered and sound a lot like cartoon ducks. As a result, you must have a special SSB receiver to listen to these transmissions. Although this was often difficult for the amateur radio operators of the 1950s to obtain, it is no longer a problem with today’s modern SSB transceivers.

Broadcasters Need Fidelity.

You might wonder why SSB modulation is used for some applications and AM is used for broadcasting. Broadcasters must have excellent audio fidelity when transmitting music; otherwise, the typical radio listener will tune to another station. In order to achieve excellent fidelity when transmitting music, both sidebands and the carrier are necessary.

To produce this AM signal, the transmitter is, in effect, working as three transmitters: one to produce a strong carrier for each of the sidebands, an upper sideband, and a lower sideband. The result is that approximately half of the transmitter power is “wasted” on a blank carrier and the rest of the power is divided between the two sidebands. As a result, the actual audio output from a 600-watt AM transmitter (300 watts of carrier + 150 watts on each sideband) would be the same as the 150-watt SSB transmitter.

SSB’s High Efficiency.

Let’s run some numbers: Suppose you have a typical 5-kW broadcast transmitter. You will only be able to impress 2.5 kW of audio power on that signal. This means that each of the two sidebands will have only 1.25 kW of power. But in highly effective communications using single sideband, a single sideband signal removes the carrier and one sideband and concentrates all of its energy in one sideband. Thus, a 1-kW SSB signal will “talk” as far as a 4-kW conventional AM or FM transmitter. It is one reason why long distances can be covered effectively with SSB.

Single sideband’s benefit is not only evident on transmission. The reverse happens on receive. When you work out the math, the efficiency with an SSB signal is 16 times greater than with a conventional AM signal.

HF Signal Characteristics.

HF (high frequency) is synonymous with the more familiar term, shortwave. The only difference is that HF is the term typically used for two-way and point-to-point communications. Shortwave is typically used when referring to broadcast stations in the same range. In amateur radio, both terms are frequently used.

The HF band extends from 1700 to 30,000 kHz (1.7 to 30 MHz). To give some perspective to these numbers:

The AM broadcast band runs from 540 to 1630 kHz.

The Citizen’s Band (CB) runs from 26,960 to 27,230 kHz (within the HF band).

Television channel 2 is on 54,000 kHz. (in the VHF band).

Each of these sample frequencies has different characteristics, and it is vitally important to learn this information so that you can effectively use the HF spectrum. When talking about HF, most people list the frequencies in either kHz (kilohertz) or MHz (megahertz). This is a matter of convenience only. The base rate for frequency is the hertz (Hz), named after Heinrich Hertz, an important “father of radio.” One kHz equals 1000 Hz and one MHz equals 1,000 kHz (1 million Hz).

Radio Waves.

The Hz divisions of the radio spectrum relate directly to the frequency. Signals such as light, radio, and sound are all waves. These waves travel through the air in a manner that is somewhat similar to waves in a pond. Each radio wave has a peak and a valley. The length of each radio wave is (not surprisingly) known as the wavelength. Radio waves travel at the speed of light, so the longer each wave is, the fewer waves can arrive in one second. The number of waves that arrive per second determines the frequency.

Although the wavelength and the frequency are different ways of saying the same thing, wavelengths for radio are rarely given. In the 1920s through the 1940s, the wavelength was more frequently used than the frequency. This was probably the case because the wavelength seemed like a more tangible measurement at the time. The wavelength of the radio signal is also important because it determines the length of the antenna that you will need for receiving and especially for transmitting.

Because of the signal characteristics on the AM and FM broadcast bands, combined with the less effective internal antennas, radio signals are often thought of as being used for primarily local reception (100 miles or so). However, with two-way communications in the HF band, you are not listening for entertainment to the strongest station that you can find. You are attempting to communicate with a particular station under what could be life-threatening circumstances.

In the 1910s and 1920s, most radio enthusiasts thought that the wavelengths below 180 meters were useless, that the frequencies above the top of today’s AM broadcast band were unusable. Little did they know that the opposite was true for communications over medium to long distances. These pioneers were mislead because they didn’t yet understand the methods by which radio waves travel.

Quadrature Amplitude Modulation (QAM)-

Brief Discussion
I & Q modulation, A.K.A., QAM, is a method for sending two separate (and uniquely different) channels of information.
As you know, the carrier is shifted to create two carriers: sin and cos versions.

The two modulation inputs (analog or digital) are applied to two separate balanced modulators (BM) each of which are supplied with the sin or cos carriers, i.e., modulator #1 is supplied with the sin carrier and modulator #2 is supplied with the cos carrier.

The outputs of both modulators are algebraically summed; the result of which is now a single signal to be transmitted, containing the I & Q information.

This signal is for all intents and purposes a ‘Double Sideband Signal’ (DSB) with or without a carrier (reduced).

In the case of color television chroma, the subcarrier is transmitted as a very short burst (8 to 9 alternations); the reconstituted carrier is derived from this burst at the receiver.

This method of modulation has the advantage of reducing or eliminating intermodulation interference caused by a continuous carrier near the modulation sidebands.

Upon reception, the composite signal ( I & Q) is processed to extract a carrier replica which is again shifted in phase to create both sin and cos carriers.

These carriers are applied to two different demodulators; each demodulator outputs one of the two original signals applied in the modulation process (I & Q) at the transmitter.

In the more recent incarnations of the QAM or I & Q modulation techniques, an Analog to Digital Convertor (ADC) is used to first convert the analog input to a serialized digital bit stream and is applied to the QAM modulators; likewise at the receiver.