Coaxial cable

Coaxial cable or is an electrical cable consisting of a round conducting wire, surrounded by an insulating spacer, surrounded by a cylindrical conducting sheath, usually surrounded by a final insulating layer (jacket). It is used as a high-frequency transmission line to carry a high-frequencybroadband signal. Because the electromagnetic field carrying the signal exists (ideally) only in the space between the inner and outer conductors, it cannot interfere with or suffer interference from external electromagnetic fields.

Description

Coaxial cables may be rigid or flexible. Rigid types have a solid sheath, while flexible types have a braided sheath, usually of thin copper wire. The inner insulator, also called the dielectric, has a significant effect on the cable's properties, such as its characteristic impedance and its attenuation. The dielectric may be solid or perforated with air spaces. Connections to the ends of coaxial cables are usually made with RF connectors.

Signal propagation

Radio-grade flexible coaxial cable. A: outer plastic sheath B: copper screen C: inner dielectric insulator D: copper core

Open wire transmission lines have the property that the electromagnetic wavecharacteristic impedance. They also cannot be run along or attached to anything conductive, as the extended fields will induce currents in the nearby conductors causing unwanted radiation and detuning of the line. Coaxial lines solve this problem by confining the electromagnetic wave to the area inside the cable, between the center conductor and the shield. The transmission of energy in the line occurs totally through the dielectric inside the cable between the conductors. Coaxial lines can therefore be bent and moderately twisted without negative effects, and they can be strapped to conductive supports without inducing unwanted currents in them. In radio-frequency applications up to a few gigahertz, the wave propagates only in the transverse electric magnetic (TEM) mode, which means that the electric and magnetic fields are both perpendicular to the direction of propagation. However, above a certain cutoff frequency, transverse electric (TE) and/or transverse magnetic (TM) modes can also propagate, as they do in a waveguide. It is usually undesirable to transmit signals above the cutoff frequency, since it may cause multiple modes with different phase velocities to propagate, interfering with each other. The outer diameter is roughly inversely proportional to the cutoff frequency. propagating down the line extends into the space surrounding the parallel wires. These lines have low loss, but also have undesirable characteristics. They cannot be bent, twisted or otherwise shaped without changing their

The outer conductor can also be made of (in order of decreasing leakage and in this case degree of balance): double shield, wound foil, woven tape, braid. The ohmic losses in the conductor increase in this order: Ideal conductor (no loss), superconductor, silver, copper. It is further increased by rough surface (in the order of the skin depth, lateral: current hot spots, longitudinal: long current path) for example due to woven braid, multistranded conductors or a corrugated tube as a conductor) and impurities especially oxygen in the metal (due to a lack of a protective coating). Litz wire is used between 1 kHz and 1 MHz to reduce ohmic losses. Coaxial cables require an internal structure of an insulating (dielectric) material to maintain the spacing between the center conductor and shield. The dielectric losses increase in this order: Ideal dielectric (no loss), vacuum, air, PTFE-foam, PTFE, polyethylene. It is further increased by impurities like water. In typical applications the loss in polyethylene is comparable to the ohmic loss at 1 GHz and the loss in PTFE is comparable to ohmic losses at 10 GHz. A low dielectric constant allows for a greater center conductor: less ohmic losses. An inhomogeneous dielectric needs to be compensated by a noncircular conductor to avoid current hot-spots.

CONNECTOR

From the signal point of view, a connector can be viewed as a short, rigid cable. The connector usually has the same impedance as the related cable and probably has a similar cutoff frequency although its dielectric may be different. High-quality connectors are usually gold or rhodium plated, with lower-quality connectors using nickel or tin plating. Silver is occasionally used in some high-end connectors due to its excellent conductivity, but it usually requires extra plating of another metal since silver readily oxidizes in the presence of air.

One increasing development has been the wider adoption of micro-miniature coaxial cable in the consumer electronics sector in recent years. Wire and cable companies such as Tyco, SumitomoHitachi Cable, Fujikura and LS Cable all manufacture these cables, which can be used in mobile phones. Electric,

Radio propagation

Radio propagation is a term used to explain how radio waves behave when they are transmitted, or are propagated from one point on the Earth to another.

In free space, all electromagnetic waves (radio, light, X-rays, etc) obey the inverse-square law which states that the power density of an electromagnetic wave is proportional to the inverse of the square of "r" (where "r" is the distance [radius] from the source) or:

Doubling the distance from a transmitter means that the power density of the radiated wave at that new location is reduced to one-quarter of its previous value.

The far-field magnitudes of the electric and magnetic field components of electromagnetic radiation are equal, and their field strengths are inversely proportional to distance. Doubling the propagation path distance from the transmitter reduces their received field strengths by one-half. The reduction of each of these fields by one-half is the result of the power density reduction to one-quarter over that doubled path length.

Electromagnetic wave propagation is also affected by several other factors determined by its path from point to point. This path can be a direct line of sight path or an over-the-horizon path aided by refraction in the ionosphere.

Lower frequencies (between 30 and 3,000 kHz) have the property of following the curvature of the earth via groundwave propagation in the majority of occurrences. The interaction of radio waves with the ionized regions of the atmosphere makes radio propagation more complex to predict and analyze than in free space. Ionospheric radio propagation has a strong connection to space weather.

Since radio propagation is somewhat unpredictable, such services as emergency locator transmitters, in-flight communication with ocean-crossing aircraft, and some television broadcasting have been moved to satellite transmitters. A satellite link, though expensive, can offer highly predictable and stable line of sight coverage of a given area (see Google Maps for a "real-world" application).

A sudden ionospheric disturbance is often the result of large solar flares directed at Earth. These solar flares can disrupt HF radio propagation and affect GPS accuracy.

Antenna

The beginning and end of a communication circuit is the antenna. The antenna can provide gain and directivity on both transmit and receive. The take-off angle of the antenna is based on the type of antenna, the height of the antenna above ground, and the terrain below and in front of the antenna. The take-off angle will determine the angle of incidence on the ionosphere, which will affect where the signal will be refracted by the ionosphere.

Radio frequencies and their primary mode of propagation

Band		Frequency	Wavelength	Propagation via
VLF	Very Low Frequency	3 – 30 kHz	100 – 10 km	Guided between the earth and the ionosphere.
LF	Low Frequency	30 – 300 kHz	10 – 1 km	Guided between the earth and the D layer of the ionosphere. Surface waves.
MF	Medium Frequency	300 – 3000 kHz	1000 – 100 m	Surface waves. E, F layer ionospheric refraction at night, when D layer absorption weakens.
HF	High Frequency (Short Wave)	3 – 30 MHz	100 – 10 m	E layer ionospheric refraction. F1, F2 layer ionospheric refraction.
VHF	Very High Frequency	30 – 300 MHz	10 – 1 m	Direct wave.
UHF	Ultra High Frequency	300 – 3000 MHz	100 – 10 cm	Direct wave.
SHF	Super High Frequency	3 – 30 GHz	10 – 1 cm	Direct wave.
EHF	Extremely High Frequency	30 – 300 GHz	10 – 1 mm	Direct wave limited by absorption.

High frequency (HF)

High frequency (HF) radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters. Shortwave (2.310 - 25.820 MHz) overlaps and is slightly lower than HF.

Since the ionosphere often reflects HF radio waves quite well (a phenomenon known as skywave), this range is extensively used for medium and long range terrestrial radio communication. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors:

• Sunlight/darkness at site of transmission and reception
• Transmitter/receiver proximity to terminator
• Season
• Sunspot cycle
• Solar activity
• Polar aurora
• Maximum usable frequency
• Lowest usable high frequency
• Frequency of operation within the HF range

The high frequency band is very popular with amateur radio operators, who can take advantage of direct, long-distance (often inter-continental) communications and the "thrill factor" resulting from making contacts in variable conditions. International shortwave broadcasting utilizes this set of frequencies, as well as a seemingly declining number of "utility" users (marine, aviation, military, and diplomatic interests), who have, in recent years, been swayed over to less volatile means of communication (for example, via satellites), but may maintain HF stations after switch-over for back-up purposes. However, the development of Automatic Link Establishment technology based on MIL-STD-188-141A and MIL-STD-188-141B for automated connectivity and frequency selection, along with the high costs of satellite usage, have led to a renaissance in HF usage among these communities. The development of higher speed modems such as those conforming to MIL-STD-188-110B which support data rates up to 9600 bps has also increased the usability of HF for data communications. Other standards development such as STANAG 5066 provides for error free communications through the use of ARQ protocols.

CB radios operate in the higher portion of the range (around 27 MHz), as do some studio-to-transmitter (STL) radio links. Some modes of communication, such as continuous wave morse code transmissions (especially by amateur radio operators) and single sideband voice transmissions are more common in the HF range than on other frequencies, because of their bandwidth-conserving nature, but broadband modes, such as TV transmissions, are generally prohibited by HF's relatively small chunk of electromagnetic spectrum space.

Noise, especially man-made interference from electronic devices, tends to have a great effect on the HF bands. In recent years, concerns have risen among certain users of the HF spectrum over "broadband over power lines" (BPL) Internet access, which is believed to have an almost destructive effect on HF communications. This is due to the frequencies on which BPL operates (typically corresponding with the HF band) and the tendency for the BPL "signal" to leak from power lines. Some BPL providers have installed "notch filters" to block out certain portions of the spectrum (namely the amateur radio bands), but a great amount of controversy over the deployment of this access method remains.

The electromagnetic spectrum

Radio waves are a form of electromagnetic radiation, created whenever a charged object (in normal radio transmission, an electron) accelerates with a frequency that lies in the radio frequency (RF) portion of the electromagnetic spectrum. In radio, this acceleration is caused by an alternating current in an antenna. Radio frequencies occupy the range from a few tens of hertz to three hundred gigahertz, although commercially important uses of radio use only a small part of this spectrum.^[3] Other types of electromagnetic radiation, with frequencies above the RF range, are microwave, infrared, visible light, ultraviolet, X-rays and gamma rays. Since the energy of an individual photon of radio frequency is too low to remove an electron from an atom, radio waves are classified as non-ionizing radiation.

How to Install Hf and VHF in one Tower?

Please see my pictures how to intall VHF and HF in same tower

Dead air

This article is about the technical phenomenon, for the Iain Banks novel see Dead Air.

Dead air is a phenomenon whereby a broadcast which normally carries audio or video unintentionally becomes silent or blank (also known as unmodulated carrier). The term is most often used in cases where programmed material comes to an unexpected halt, either through operator error or for technical reasons, although it is also used in cases where a broadcaster has 'dried up'. It is the duty of all concerned to rectify the problem as quickly as possible; in many parts of the world dead air is considered to be one of the worst crimes a broadcaster can commit.

This is different from being off-the-air. When a station is off the air, the transmitter is not active and there is no signal at all. Dead air is where a carrier signal is being transmitted, but there is no modulation of that signal.

In the United Kingdom, any radio station which transmits dead air for more than ten minutes without rectifying the situation, broadcasting an announcement, or otherwise warning its listeners, can be penalised and may be fined up to £25,000 per minute by the independent regulator and competition authority for UK communications industries, Ofcom.

Dead air can also apply to television broadcasting, generally when a television channel has an interruption to its output, resulting in a blank screen or in the case of digital television, a frozen image, until output is restored or an apology message is broadcast.

Having dead air during commercials or sponsorship announcements can cost networks considerable advertising revenue.

Examples

An example of dead air was a Chris Evans radio transmission for the British Virgin Radio station. As a promotional stunt, Evans did not arrive for work, and his show went to air carrying nothing for about twenty five minutes.

Another case was BBC Radio 4's failure to broadcast Big Ben's midnight chimes on New Year's Day 2003; after announcing the chimes, a technical error caused the station to fall silent for a minute. This was caused by the correct feed not being faded up. Ironically, the chimes were supposed to be coming via a new link which the BBC had just installed to Westminster just to avoid cases of dead air.

On September 11, 1987, Dan Rather walked off the set of the CBS Evening News when a late running U.S. Open tennis match threatened to delay the start of his news broadcast. The match then ended sooner than expected but Rather was gone. The network broadcast six minutes of dead air before Rather was found and returned to the studio. There was considerable criticism of Rather for the incident.

Batteryless radio

A Baygen clockwork radio with crank in winding position

Radio receivers were originally operated by battery. The term batteryless radio was initially used for the radio receivers which could be used directly by AC mains supply (mains radio).

It was invented by Edward S. Rogers, Sr. on April 8, 1925 in Canada who made world history when he and his two chief engineers built the world’s first all-electric radio. The unit operated with 5 Rogers AC Vacuum tube and the Rogers Battery-Eliminator Power Unit (power supply). This unit later becomes marketed for $120 [1] as "Type 120". Batteryless Radio were not introduced in the United States until May, 1926 and then in Europe in 1927.[2]

Crystal radio receivers are a very simple kind of batteryless radio receiver. They do not need a battery or power source, except for the power that they receive from radio waves using their long outdoor wire antenna.

Thermoelectricity was widely used in the remote parts of the Soviet Union from the 1920s to power radios. The equipment comprised some bi-metal rods, one end of which could be inserted into the fireplace to get hot with the other end left out in the cold.

After second world war, kerosene radios were made in Moscow for use in rural areas. These all-wave radios were powered by the kerosene lamp hanging above it. A group of thermocouples was heated internally to 570 degrees by the flame. Fins cool the outside to about 90 degrees. The temperature differential generates enough current to operate the low-drain receiver.[3]

Foot operated radio or Pedal radio were once used in Australia. Another way of achieving the same function is Clockwork radio, hand crank radio and solar radio [4].

A modern crystal radio set

SWR Meter

Equipment for Radio Technician, but if you install HF Codan it's not need.
Because in HF-SSB Codan is include at Handle Mic.

The Bird Model 43 THRULINE® directional wattmeter is a portable insertion-type instrument for measuring forward and reflected power in coaxial transmission lines. It will accurately measure RF power under any load condition. Plug-in elements are available to fit your frequency and power needs. The more common ones are listed below.

The Bird Model 43 N is shown left with optional elements (sometimes called slugs). This model features N connectors for input and output.

The plug-in elements (slugs) determine the power rating and frequency range of the Bird 43 wattmeter. A few of the more common ones are listed below.