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This review talkabout 22-Channel FRS/GMRS 2-Way Radios (Pair) that Up to a 35-mile range ,121 privacy codes, iVOX voice-activated control, emergency alert, and many others thing you can read full review of product at here!!.
There are two major formats for two-way radios. They are Ultra High Frequency (UHF) radio and Very High Frequency (VHF) radio. Neither frequency band is inherently better than the other. They each have their pluses and minuses. Both formats are effective ways to communicate with another person. But how do you decide which one will fit your needs? Let's go over the key components of both frequencies to help you decide.
Two-way radios communicate with each other through use of radio waves. Radio waves have different frequencies, and by tuning a radio receiver to a specific frequency you can pick up a specific signal.
Radio waves are transmitted as a series of cycles, one after the other. You will always see the "Hz" abbreviation used to indicate the frequency of a radio. Hertz is equal to one cycle per second.
Radio waves are measured by kilohertz (kHz), which is equal to 1000 cycles per second, or megahertz (MHz), which is equal to 1,000,000 cycles per second--or 1000 kHz. The relationship between these units is like this: 1,000,000 Hertz = 1000 kilohertz = 1 megahertz.
You may also hear the term "wavelength" when you hear about radio waves. This term is from the early days of radio when frequencies were measured in terms of the distance between the peaks of two consecutive cycles of a radio wave instead of the number of cycles per second. Lower frequencies produce a longer wavelength.
While wavelength measures distance between the peaks of cycles, frequency refers to how long the measured time is between the "crest" and "trough" of a wave arriving at the source. So frequency measures time instead of distance, but they are essentially both saying the same thing.
What is significant about wavelength for two-way radios is that it affects transmission range under certain conditions. A longer wavelength as a general rule lets a radio signal travel a greater distance.
Lower frequencies or wavelengths have greater penetrating power. That's one of the reasons they are used for communicating with submarines. VLF radio waves (3-30 kHz) can penetrate sea water to a depth of approximately 20 meters. So a submarine at shallow depth can use these frequencies.
So from what you read above you may think VHF is always the better choice for a two-way radio no matter where you are using it. That's not necessarily true. Even though VHF has better penetrating capabilities, that doesn't necessarily make it the better choice for buildings. Remember the conversation about wavelength above? Wavelength has a big impact on transmission.
To explain this let's assume we are communicating from one side of a commercial building to the other. In between these two points is a metal wall with a three foot door in it. Metal is an enemy to radio waves and they typically don't pass through it.
For our example let's assume that the UHF wavelength the radio uses is about a foot and a half long and a similar VHF radio is around five feet long. These are in the ballpark of their normal wavelengths.
When the UHF transmits its signal the foot and a half long wave will pass through the door since the door is wider than the wavelength. The VHF signal will be totally reflected since it is wider than the opening to the door.
Your microwave oven is an example of this. The glass front door has a metal mesh with very small holes. Microwaves being a very high frequency have wavelengths that are only several inches long. The mesh keeps the microwaves trapped in the oven but it allows you to see inside because light waves have a microscopic wavelength.
Just imagine walking through the building carrying a five foot wide pole. You will encounter the same challenges a VHF signal encounters. Now imagine walking through the building with a pole that's only a foot and a half wide like a UHF wave. There are lots fewer doorways you couldn't get through.
The one difference is that wireless signals will penetrate through drywall, masonry, human bodies, furniture, wall paneling, and other solid objects. All these objects will reduce the signal strength though. The more dense the object, the more it reduces the signal. VHF will penetrate these obstacles better than UHF, but that doesn't necessarily mean that VHF is better for indoor applications as we will talk about in the UHF section below.
In our example above we assumed you had a metal wall with an opening. If you reverse this and you have a three foot metal object in front of the transmitting radio, then VHF would win. Since the object is three foot wide it will totally block the UHF signal whereas the VHF signal will get around it. Lower frequencies such as VHF diffract around large smooth obstacles more easily, and they also travel more easily through brick and stone.
For most applications, lower radio frequencies are better for longer range. A broadcasting TV station illustrates this. A typical VHF station operates at about 100,000 watts and has a coverage radius range of about 60 miles. A UHF station with a 60-mile coverage radius requires transmitting at 3,000,000 watts.
So there is no clear choice for which is better, VHF or UHF. There is a lot of "black magic" to radio technology so it's not always easy to tell which will work better for your application. To help you decide on the best technology for you, more detail about each one is included below.
UHF Radio
UHF equipment operates between the frequencies of 300 MHz and 3000 MHz. Until recently, it wasn't widely used. Now, the UHF radio frequency is used for GPS, Bluetooth, cordless phones, and WiFi.
There are more available channels with UHF so in more populated areas UHF may be less likely to have interference from other systems. If you are in an area where population is thin, VHF should work fine for you. Not too long ago the FCC also opened up a new VHF frequency called MURS that is so far not heavily used in most areas. There's more about MURS below in the VHF section. If you are in an area where interference from other radios may be an issue, UHF transmitters and receivers could be your best choice unless you use a MURS VHF radio. UHF is better at squeezing through physical barriers like walls, buildings, and rugged landscape. Anything that obstructs a radio wave, will weaken a radio signal. UHF lessens that effect. Though it may not travel as far, UHF radio waves will traverse around obstacles better than VHF.
To highlight the differences in indoor range, below is an excerpt from a brochure of a leading two-way radio maker on the predicted range of one of their lines of handheld VHF and UHF two-way radios:
"Coverage estimates: At full power, line-of-sight, no obstructions the range is approximately 4+ miles. Indoor coverage at VHF is approximately 270,000 sq ft and 300,000 sq ft at UHF. Expect about 20 floors vertical coverage at VHF and up to 30 floors at UHF. Note: Range and coverage are estimates and are not guaranteed."
VHF waves are not very good at finding their way around walls, buildings and rugged landscape. Therefore range will be significantly reduced for VHF radios in these environments. That may not necessarily be a problem if the range needed is only a few hundred feet. You can also add an external antenna to an indoor VHF base station that will reduce or eliminate this problem.
One of the downsides to UHF is that the FCC requires you to get a license to operate in these frequencies. Although many frequencies in the VHF business band also require a license. If you choose a radio in the VHF MURS frequencies you can operate it without a license. UHF equipment is usually more expensive. The components need to be finely tuned and are more expensive to construct. This does not mean it's necessarily better, just more expensive.
One advantage of UHF transmission is the physically short wave that is produced by the high frequency. That means the antenna on the radio can be shorter than an equivalent VHF radio.
VHF Radio
VHF equipment operates between the frequencies of 30 MHz and 300 MHz. FM radio, two-way radios, and television broadcasts operate in this range.
Both UHF and VHF radios are prone to line of sight factors, but VHF a little more so. The waves make it through trees and rugged landscapes, but not as well as UHF frequencies do. However, if a VHF wave and a UHF wave were transmitted over an area without barriers, the VHF wave would travel almost twice as far. This makes VHF easier to broadcast over a long range. If you are working mostly outdoors, a VHF radio is probably the best choice, especially if you are using a base station radio indoors and you add the external antenna.
Since VHF has been around longer and isn't as complicated to make, equipment is usually cheaper when compared to similar UHF equipment. One disadvantage to this equipment can be its size. Since the frequency waves are bigger, an antenna must be bigger.
VHF radios also have a smaller number of available frequencies. Interference with other radios could be more likely to be a problem. However, the FCC recently made this less of a problem when they opened up the MURS frequencies. The 150 MHz frequency is a Citizens Band radio spectrum that is called the MURS service. MURS stands for Multi-Use Radio Service. This service is for use in the United States and Canada. It is a low power, short range service in the VHF 150 MHz Citizens Band radio spectrum. There are 5 channels in the MURS frequencies with 38 privacy codes under each one that enable you to only pick up conversations on your code. The FCC does not require users of products for MURS to be licensed.
With MURS you can add a larger or external antenna to improve range. If you want to put an antenna on top of your house or business, you can do it with MURS. Some antenna manufacturers claim an external antenna can increase the effective radiated power of a transmitter by a factor of 4. These MURS intercoms can transmit up to four miles, and perhaps more with an external antenna depending on the terrain.
One benefit of VHF wireless radios is that battery life is almost always better than for similar UHF units. For handheld radios this is a plus.
VHF equipment is usually lower cost for those on a budget. Equipment can be more economical than similar UHF products.
In summary, if you are planning on using your two-way radios mainly inside buildings, then UHF is likely the best solution for you. If you are mainly using your two-way radios for communication outside, then VHF would be a good choice. Either radio technology can work for you if you don't really have a long range to cover. In that case you may want to choose VHF for it's lower cost.
Radios are one of the first types of communication to be invented that are still used in the modern age. The main reason for this is because of the ease of use and the low cost it takes to use it. They are a very important component of many businesses such as the construction industry.
In the construction industry the person operating the crane is very high up and most defiantly out of reach of and site manager giving the instructions below. Some people might suggest the use of mobile phone for communication but the cost per day would be too high for it to be a viable option. Instead you can use a radio for communication as it would be very cheap, in fact all it would cost is the initial price of the radio sets at the shop. If you do decide to buy a radio set then make sure that it is rechargeable as buying multiple batteries per week for the use of the radio is also very expensive.
When in pursuit of a criminal the police use radio communications in order to coordinate themselves around the suspect in order to increase their chances of catching him. It can also be use for calling for backup and is one of the first things that are used when a dangerous situation occurs. This just goes to show how important these devices are for this type of job, without them many different produces would have to be changed in order to get the job done to the same standard.
Office machines are basically the core of what makes office environments tick. Some of these machines include copiers, fax machines, telephone systems, computer systems, and intercoms among other things. All of these machines have their own function and contribution to what they bring to the office.
Copiers are machines that make identical paper copies of any document fed into its system. This includes pictures and text articles alike. Most copiers today use a special type of technology known as xerography which is a dry process that uses heat to make the copies, though some copiers use ink jet printers, but the standard industrial office-used copier uses this heat process.
Fax machines are a sort of telecommunication that uses technology to transfer copies of specific documents using a telephone network. The fax system basically breaks the document fed into the machine into a series of short code and sends it over the phone line to another fax machine which duplicates this code onto a document.
Computer systems, another common office machine, are a complex network of computers that are linked together for inter and inner departmental use. Normally, the computers are all formatted and structured about the same and are then all networked together, so that every employee has the same computer and may communicate with all the computers in the system. Though, in larger companies, the quality of the computer an employee uses as well as the computer system level of advancement is determined by his or her rank in the company.
Several other miscellaneous things included in the field of office machines are phone systems, which link all the phones in a company or office together for easy access to another employee by an "extension" or an intercom, which is a two way radio implemented on two phones for frequent communication with another employee.
All of these machines fall under the umbrella of office machines, and they all contribute in one way or another to the workings of an office.
What is WiFi?
It is possible to form a somewhat informed opinion on the safety or potential risks of this new technology without actually being a physicist yourself.
Quite simply, Wi-Fi is the wireless technology most commonly used to connect people to the Internet in schools, coffee shops, hotels and other network locations, or to connect cell phone users to one another. Wi-Fi is certainly convenient for travelers and students, but is it dangerous? Many believe that the low-level electromagnetic waves that radiate from the wireless Internet source to each individual user can be harmful to your health, even causing cellular changes and possibly cancer in some cases.
The area covered by a WiFi Internet connection is known as a "hotspot"; this is the area in which the waves radiate to give users access to the world wide web. It can span several kilometers, although the waves cannot pass through treed areas. While in the hotspot, a laptop user can simply connect to the network, access the Internet, and check their Email or do their other business on the run.
A wireless network uses radio waves to send communications across a two-way network. A computer's wireless adapter translates the Internet connection data into a radio wave and sends it to the wireless router - the one in your laptop. This process works in reverse as well, sending a radio signal back to the host computer.
Hotspots Useful Stations or Environmental Hazards?
Some report an unusual sensitivity to the waves emitted in these hotspots. Officially, the levels of WiFi electromagnetic radiation emitted into the environment in a hotspot are well below recommended levels and there is no evidence of any risk to humans. Yet some people blame WiFi exposure for everything from sleep disturbances, headaches and blurred vision, to heart and breathing problems.
Because no study has ever shown a conclusive risk to human health from exposure to these low-frequency radio transmissions, many simply shrug off the complaints of these people, choosing to believe their symptoms are coincidental or caused by another source.
So just how high are the levels of radiation in a hotspot? According to Dr. Michael Clark of the HPA, the published research on mobile phones and wireless networks does not indicate a risk to human health. "All the expert reviews done here and abroad indicate that there is unlikely to be a health risk from wireless networks" he says. "The few studies on cellular phone masts that have appeared in peer-reviewed journals claiming to observe health effects are not at all conclusive. The real problem is deciding what level of precaution is appropriate.
"When we have conducted measurements in schools, typical exposures from wifi are around 20 millionths of the international guideline levels of exposure to radiation. As a comparison, a child on a mobile phone receives up to 50% of guideline levels. So a year sitting in a classroom near a wireless network is roughly equivalent to 20 minutes on a mobile. If wi-fi should be taken out of schools, then the mobile phone network should be shut down, too - and FM Radio and TV, as the strength of their signals is similar to that from wi-fi in classrooms."
You are on your way out of your home. Suddenly, you turn around and dash inside. You left something you definitely can't go out without! Is it your wallet? Well, that may top the list, but what comes next is indisputable - your cell phone.
MOst adults nowadays have a cell phone. This is one of the needs that the modern world now has. And with all of the innovations that now flood the market, sometimes you are dazzled at how far the cell phone technology has gone.
The cell phone could be traced as far back as 1947 when the researchers observed the use of car phones. So, technically speaking, the crudest form of cell phone was the first mobile car phone. And in a way, a cell phone is much like a two-way radio. In the past, there was a massive community of mobile radio users who sort of popularized the technology that would give birth to the modern cell phone.
Back then, these researchers thought that they could develop a more 'mobile' phone by the use of small cells but The Federal Communications Commission would not free the airwaves - yet. AT&T wanted to develop the technology but FCC limited the frequencies. The development of cell phones had to be shelved.
It was not until 1968 that the FCC reconsidered everything. They proposed a challenge that when a mobile phone system that really works is introduced, then they would increase the allocation of frequencies. It did work and the rest, as the saying goes, is history.
Although the history of the cell phone could be attested to this, perhaps the first known inventor of a mobile handset was Dr. Martin Cooper. Cooper worked for Motorola as a General Manager for the Systems Division and was able to develop the cell phone technology along with this colleagues Richard W. Dronsuth, Albert J. Mikulski, Charles N. Lynk, Jr., James J. Mikulski, John F. Mitchell, Roy A. Richardson and John A. Sangster.
Although it is Dr Cooper who is widely recognized for fathering the cell phone usage, it wasn't entirely an original idea of his. His rival, Joel Engel who was then the head of the researches at AT&T Bell Labs was the first to develop the electronic components of cellular technology.
It was in 1973 that the first cell phone call was made. Despite the demand for this type of technology, it took 37 years before the United States had commercial availability. By 1987, there was a bottleneck of communication. The users were simply too numerous for the existing allowed frequencies.
There are 3 known generations to the cellular technology:
The First Generation - the first mobile phone to make contact was the Motorola DynaTAC 8000X. This was a development from the same phone that Dr Cooper used to make the historical 'first cell phone call'. It was in the 1980's that cell phones made use of networks with several closely located base stations. Analog systems were then used. Back then, mobile phones were more like 'car phones' basing on the size and the use of the gadgets. Not long after, these car phones were designed to fit a carrier the size of a briefcase. This innovation made the phones become more 'mobile'.
The Second Generation - the second wave presented the introduction of GSM cell phones. The very first digital cell phone was introduced in the United States in 1990. Europe followed with the establishment of a digital network in 1991.
The Third Generation - or what is popularly called the 3G. This paved the way for the development of such technologies as live streams of television and radio feeds. These are just two of the many known developments that we have today.
Now that you know where your cell phone originated from and what it can offer you now, the next thing to know would probably be the future. It is currently predicted that by the year 2010, wirelines will be near extinction and cell phones will take over. Another forecast is that overseas calls would be uninterrupted and that would be made possible by the massive development on reception and areas of coverage. And guess what? You might be able to operate your dishwasher in the future with the use of your cell phone!
The possibilities are endless. This is not only true with cell phones but all other forms of technology as well. With the gifted minds that are always turning impossible to possible, the future will surely be a much better and more exciting place to live in!
When deciding to add a new wireless intercom system to the ever increasing portfolio of wireless devices in your home or business, you need to first think about the compatibility with the products you already have (or your close neighbors have). You also need to consider the range and features you need.
Wireless Intercom Frequencies
In the United States there are several frequency ranges for wireless products for unlicensed consumer use. They are 49MHz, 900MHz, 2.4GHz, 5.8GHz, and Family Radio Service (FRS) band. Most recently the FCC added the Multi-Use Radio (MURS) service. Radio frequencies for devices are similar in Canada, but MURS cannot be used there.
Back when consumer wireless products were first introduced, these wireless products used the 49MHz frequency spectrum. Early cordless telephones used this spectrum and it is still used by cheap baby monitors and other low-end wireless units. It has a short range and is prone to lots of interference. You won't likely find wireless intercom systems that use this spectrum anymore, or if you do, you won't want them.
Later, 900 MHz products using analog transmission technology arrived on the market. Neither the 49MHz or these early 900Mhz products have any form of security. Anyone with a device in the same frequency can listen in to conversations. Newer digital spread spectrum 900MHz products divide digital transmission across a range of frequencies so other devices can't eavesdrop on your conversations. Digital spread spectrum intercoms also have a greater range than the analog 900Mhz units. There are at least two wireless intercoms currently on the market, but only one of them uses digital spread spectrum. The wireless intercom system that uses spread spectrum can communicate up to 1000 feet.
2.4GHz devices were next to market. There are a growing number of cordless telephones and other devices in this range. As far as intercom systems, video intercom systems are the primary users of this range although the only wireless video intercom on the market was recently discontinued. 2.4GHz is also the frequency range used by WiFi wireless data networks (802.11B/G) in homes and businesses so products in this range can interfere with each other.
The Family Radio Service (462-467MHz) is in the Ultra High Frequency (UHF) band and is basically an improvement to the old walkie talkies of long ago. These handheld radios are sold everywhere and used heavily so any intercom systems in this range would have to compete with these handheld radios (and anyone can listen in to your conversations). There are no known wireless intercoms systems that use FRS.
Now 5.8GHz products are starting to make their appearance in the cordless phone arena. No compatibility issues exist between 5.8GHz and 2.4GHz devices so no problems should be experienced in mixing them. However, there are currently no known wireless intercom systems in this range.
You'll also see some intercom systems that claim to be wireless but they really use the power wiring in your home or business to send and receive transmissions from the intercom. These are frequently called "FM wireless intercoms" even though they often transmit over your house wiring in the AM band. To use them, you just plug an AC adapter into the wall. These systems are very prone to humming or buzzing and are not recommended unless you are prepared to live with this possibility. Since house wiring comes in as 240 volts and is split in two phases of 120, you'll also experience problems with the signal trying to cross the phases. One part of your house or business may work fine, where the other half doesn't. These intercoms are typically the least expensive intercoms of the bunch.
Long Range Wireless Intercoms
The most recent addition to the wireless intercom market are products in the MURS frequency range. MURS is a service in the VHF (Very High Frequency) 150 MHz radio spectrum. MURS has a power increase of four times that of FRS radio. And unlike FRS, you can add a larger or external antenna to improve range. If you want to put an antenna on top of your house, you can do it with MURS. Some antenna manufacturers claim an external antenna can increase the effective radiated power of a transmitter by a factor of 4. These MURS intercoms can transmit up to four miles, and perhaps more with an external antenna.
The Federal Communications Commission (FCC) in the United States does not require you obtain a license to use MURS frequencies so you will not have to go through that process.
There are 5 MURS channels and 38 interference eliminator or "quiet codes" that can be used on each of these channels. These quiet codes keep your radios quiet unless another radio is programmed on the same channel and quiet code. Chances are you won't have to worry about these codes since MURS usage is extremely light. There are only a few makers of MURS radios, so traffic on these frequencies is hard to find in most areas.
The MURS Intercom system is the wireless intercom you need if you have a large property or you need to talk between buildings. You can use a MURS to not only communicate within a home, but to neighboring homes as well. You can even add a handheld unit to your MURS intercom system so you can stay in touch away from your home.
Long Range Wireless Outdoor Intercoms
You can also get commercial-grade wireless call boxes that communicate with two way radios and base station intercoms. These wireless callboxes are water resistant and designed for outdoor use. They can open gates or doors remotely if you have a model with a gate relay. Callboxes also come in vandal-proof housings with stainless steel front panels. The range on these is up to a mile or more if you use an external antenna. These wireless call boxes can be battery powered, powered with a AC-DC converter, or by solar power. Callboxes are available in UHF and VHF frequencies so you can match them with your existing two way radios if you have them. You can get call boxes that work in the un-licensed MURS frequencies so you can use them with your MURS intercoms or radios.
The benefit of a wireless callbox is that you save money by not having to do trenching and running expensive cable to the unit. You also don't have to pay any air-time or telephone service fees with these wireless systems. Another benefit is that since the unit is wireless, people monitoring the units can carry handheld radios that communicate with the callbox. That allows your monitoring people to be mobile.
Wireless Intercom Features
Another thing to consider is what features you need for your particular application. Commercial applications often have needs for a wider variety of features. The MURS wireless system for instance has a wide variety of products that can be used with it. Not only can you get military-grade two-way radios with lots of headset options, but you can get base station intercoms, wireless call boxes with solar power option, wireless public address systems, customer service call boxes, wireless remote switches, and motion detector devices. For less commercial or residential use, a 900MHz intercom system has outdoor intercoms and doorbell intercoms you can use with your indoor intercoms.
So the wireless intercom system you choose depends on the application you have, the wireless devices already in your home or business, the range you need to cover, as well as your budget. But, once you choose the right system, you'll be able to enjoy the convenience a wireless intercom system provides for years to come.