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.

Laptop For Radio Technician.

I'm Suggestion for Radio Technician Use this Laptop. You must buy complete with Docking Station.You can use serial 9 pin (com.1) for cable program.It's very simply if you want to install at Vehicle or your base station. IBM THINKPAD X40 Corporate quality ultra portable slimline - only 24mm thick - notebook powered by an Intel Pentium mobile 1.2Ghz processor, includes 1024MB RAM, 40gig hard drive, 12.1'' TFT display & preloaded Windows XP Professional Intel Pentium M 1200MHz processor 1024MB SDRAM DDR memory 40GB hard drive 12.1" TFT screen (1024x768 resolution) Intel integrated extreme graphics Soundblaster compatible sound & input/ouput ports UK keyboard Trackpoint pointing device 56k modem & 10/1000 network 802.11g high speed wireless network 2x USB ports (these units are bootable to USB devices) VGA & infra red ports 1x Type II PCMCIA slot & 1x SD/MMC slot Li-ion battery & AC adaptor/charger Dimensions: 268mm x 211mm x 24mm (with standard battery fitted - note the battery we supply is a high capacity unit, which protrudes slightly at the back of the unit. On request we will supply the standard lower capacity battery instead) Refurbished with 90 days RTB warranty Preloaded Windows XP Professional SP2 with COA & restore CD Does not include base unit or any CD ROM drive Windows XP pro pre-installed with COA & restore DVD

IBM/Lenovo ThinkPad X4 Dock, Compatible with all ThinkPad X40 Series Systems, Model: 250610U, ds-sy

CODAN Multi-wire Broadband Dipole HF Antenna code 463

I have experienced install this antenna at Swiss Bel Hotel Banda Aceh For EUEOM
(European Union Election Observation Mission to ACEH 2007)
It's perfect and powerful.

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CODAN 463 series Multi-wire Broadband Dipole HF Antenna is a 3-wire terminated folded dipole HF antenna designed for broadband operation in fixed stations. It is available in multiple power levels up to 1 kW. The antenna can be mounted horizontally between two support systems, or as an inverted “V” using a single central support mast.

KEY FEATURES

Durability
CODAN C463 series HF antenna is made from lightweight, weatherproof materials designed to withstand extreme environmental conditions and wind speeds greater than 200 km/hr.

The wire elements are constructed of high quality, corrosion resistant stainless steel, with balun and load housings, and insulators made from UV resistant, durable moulded plastic.

Performance
Due to the antenna’s optimum performance over a wide HF range, an antenna tuner is not required — minimising cost and setup requirements.

Antenna performance is very similar in both horizontal and inverted "V" configurations.

The inverted V configuration provides a good overall solution for most base station applications with the added benefit of only requiring a single mast for installation.

For long range operation, the horizontal configuration is recommended.

Easy to install
CODAN HF antenna is supplied completely assembled and ready for erection with an inverted V mounting arm and detailed erection instructions.

SPECIFICATIONS

Electrical

Frequency                        2–30 MHz

Power rating                     250 W PEP (125 W avg)

                                 500 W PEP (300 W avg)

                                 1 kW PEP (600W avg)

Nominal impedance                50 .

VSWR                             Generally less than 2:1

RF connector type                SO239

Mechanical

Length m (ft)                    28 (91.9) insulator to insulator

Width m (ft)                     1.3 (4.27)

Minimum mast spacing m (ft)      30 (98.5)

Recommended mast height m (ft)   10–12 (32.8–39.4)

Wind rating                      200 km/hr (125 ml/hr)

Packed weight                    6.7 kg

Carton dimensions                1435 mmx 165 mm x 165 mm

Mounting hardware                Halyard, pullies and mounting arm supplied

SCOTTEVEST Solar Panels Voltaic Solar Bags

How do you think if you use this Equipment in Emergency area?OK?
The solar panels enable you to recharge your USB compatible devices on the go, either while wearing the jacket or with the panels removed. When attached, the solar panels compliment the jacket’s design. The solar panels charge a small battery - about the size of a deck of cards. The battery powers your device almost immediately after the solar panels are exposed to sunlight. Once the battery is fully charged, the panels can be removed and your portable electronic device can tap into the stored power.

Typical charge times in direct sunlight range from 2-3 hours, but direct sunlight is not required. The battery pack can charge any device compatible with Universal Serial Bus (USB) chargers, including cell phones, PDAs, Game Boys, MP3 players, and other mobile devices. (NOTE: USB cables are not included, but are readily available from numerous sources, including www.ziplinq.com, www.belkin.com, and Radio Shack). Also, check out our latest accessory, the Zipcord Retractable Mobile Phone USB Charger.

The solar panels can be attached to the following SeV jackets:

SCOTTEVEST Tactical 4.0 Jacket
SCOTTEVEST Classic Vest 4.0

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Voltaic Solar Bags

The Voltaic solar bags are mobile power generators, designed to charge your devices without tying you to a power outlet, which makes them ideal for traveling.

Just plug a standard car charger into the bag and recharge most small electronic devices including: cell phones, cameras, two way radios, PDA's, and MP3s. Note: it is not designed to charge laptops.

If you don't have a car charger, the bags come with a set of 11 standard adaptors for common cell phones and other devices. We also offer a full range of optional adaptors.

Embedded in the outside of the bags are three lightweight, tough, waterproof solar panels which generate up to 4 watts of power. This means quicker charge times!

Included with each bag is a Li Ion battery pack which stores any surplus power generated, so it is available when you need it - not just when the sun is up. The battery pack can also be charged using an AC travel charger or car charger (both included). This makes the Voltaic bags just as useful on the grid as off.

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Battery Pack

The battery pack clips inside the back pocket of the Voltaic solar bags and allows it to function as a mobile power reservoir, not just a solar charger.

Inside the battery pack is a 4,400m Ah at 3.6 volts Li Ion battery.
It includes:

A voltage converter with three settings 3.5, 5 and 7.2 Volts,

A charge indicator, and

A built-in LED torch.

Adapters/Chargers

The Voltaic backpack comes with a set of standard adaptors pictured here. To charge a device you can use a standard car charger, or a USB charger. There are also direct adaptors for popular cell phones, and a set of universal adaptors.

It also includes an AC travel charger and a car charger for charging the battery when solar charging is not practical.

In addition to these standard items, we offer a range of optional adaptors for cell phones, cameras, PDA's etc.

Solar Panels

Integrating the solar panels into the back pocket of the bag is a key (patent pending) innovation of the Voltaic backpack. It means that unlike a typical solar charger:

There is no need to unpack and setup the panels

There is no need to stay in one place, and

All of your devices can stay securely inside the bag.

The panels are built into the back of the bag in a way that allows them to articulate, so the bag itself does not feel stiff or restrictive.

They generate up to 4 watts of power, enough to charge most portable electronics (other than laptops). A typical cell phone will take 4-6 hours to charge in direct sun- see approximate charging times.

The panels are built on a strong but lightweight
aluminum plastic composite, specifically selected to withstand the rigors of outdoor use.

SATELLITE PHONES

This Satellite phones allowed by UN and most important for you travel in danger area

Iridium Phones
Go anywhere!

Iridium’s satellite network is the only truly global communications network providing voice, paging, 160-character two-way short text messaging (SMS), emergency 911 service (dial sequence 00-911) and internet access services to subscribers anywhere on the surface of the earth. Even the polar caps have Iridium coverage!

The Iridium 9505A is smaller, more power efficient and more water resistant than the ground-breaking original Iridium phone, the Iridium 9500. The internet access is 2400 bps (direct dial circuit switched) or 10,000 bps^* with our free SkyFile compression and email software. Includes: Iridium 9505, universal AC charger and international plug kit, high cap battery, mag-mount car antenna (with 1.5 meter cable), antenna adapter, DC charger, belt holster, hands free earpiece, and manual.

Options: external mast antennas (U-bolt and thread mount types), antenna cables, mag-mount vehicular antennas, high capacity batteries, external battery packs, watertight Pelican impact case, portable solar chargers, and fixed-site Iridium phones for PBX applications

Technorati Profile

How to describe how good an antenna is?

Four ”figures” describe how good an antenna is compared to the required performance: SWR = Standing wave ratio D = Directivity G = Gain BW = Bandwidth (We will not deal with the term ”polarisation” in this respect).

SWR If the impedance of the antenna is different from the impedance of the cable, the antenna will reflect back some of the induced energy through the feeder cable to the transmitter, which naturally is undesirable. Normally, the impedance of the cable is 50 Ω. If Ra indicates the impedance of the antenna, the standing wave ratio is defined as: SWR = Ra/50 Ω (if Ra is more than 50 Ω) SWR = 50/Ra Ω (if Ra is less than 50 Ω) Examples: If Ra = 50 Ω is SWR = 1.0 If Ra = 100 Ω is SWR = 2.0 If Ra = 25 Ω is SWR = 2.0 Consequently, it is of importance that the SWR is as close to 1.0 as possible thus obtaining the highest power being transmitted from the cable to the antenna.

Directivity D

The directivity D is an indication of the capability of the antenna to conduct the radiated power ”to a certain site”.

Normally, omnidirectional or directional antennas are mentioned.

Omnidirectional:
An omnidirectional antenna with high directivity has a radiation being similar to a pancake.

Directional:
A directional antenna with high directivity has a radiation being similar to the cone of light from a projector.

Omnidirectional	Omnidirectional	Omnidirectional
Directional	Directional

Gain G The gain of an antenna is defined as G = η x D, where η indicates the efficiency of the antenna. Consequently, in the gain value possible loss in the antenna is comprised. The η-figure is always less than the directivity. For most antenna types the own loss is so low that G = D can be considered.

Bandwidth The bandwidth of the antenna is the frequency range, in which it operates properly, i.e. both gain and SWR are within the more specified limits.

Antennas for Mobile Units

Land Mobile Antennas Quarter-wave Antennas: The most common vehicle antennas utilize the car roof as one half of the antenna system. The antenna is a so-called ”monopoly on ground plane”. The basic type is a so-called quarter-wave ( ¼ λ) antenna. The fact that the antenna being close to 50 Ω is utilized when the whip has a length of approx. 1/4 wave length at the operating frequency. By lengthening the whip, the antenna gain will be increased. The gain will, however, again be reduced if the whip length is above 5/8 wave length.
Colinear Antennas: In case higher gain should be achieved, so-called ”colinear” antennas should be applied, for which more radiating elements are stacked and operate together, thus concentrating the radiation in the horizon. The optimum mounting site is in the centre of the car roof, at which the optimum omnidirectional characteristics are achieved.
Marine Antennas Marine antennas are in a way very similar to omnidirectional base station antennas except for the fact that usually intensified requirements as to mechanical sturdiness and corrosionresistance are made. Marine antennas are similar to omnidirectional base station antennas but with intensified requirements of sturdines Marine antennas are similar to omnidirectional base station antennas but with intensified requirements of sturdines Maritime communication is mainly taking place on medium wave, short wave and the maritime VHF bands.
Portable Antennas Quarter-wave Antennas: Like mobile antennas portable antennas are mostly ¼ wave ”monopoly” antennas, which utilize the chassis of the portable radio as ground plane, i.e. as one half of the antenna system. This usually results in insufficient ground plane as well as the fact that the radiation from the portable radios is mostly very badly defined owing to the presence of the hand or body, and in general a low efficiency for portable antenna systems should be taken into consideration, both because of disadjustment loss and loss owing to ”overturned” radiation.
Half-wave Antennas: If, however, antenna whips with a ½ wave length are applied together with an adaptation circuit the antenna being independent of the cabinet can be achieved. The antenna functions ”in itself” and a considerable improvement of 5 dB as average value can be achieved (compared to a ¼ wave antenna on the same device).
Nowadays air craft antennas are an integrated part of the fuselage