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.
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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.
Christmas Sales Dremel 8200-1/28 12-Volt Max Cordless Rotary Tool 201
Dec 16, 2011 20:56:34
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Christmas Sales Dremel 8200-1/28 12-Volt Max Cordless Rotary Tool Feature
- Variable Speed from 5,000 to 30,000 RPM; Easy to understand speed dial with increments that correspond directly to speed
- Soft-Grip for comfort and control
- Works with standard attachments plus "high performance" level attachments, and all accessories
- Separate on/off switch allows user to "set & forget" speed setting
- Removable Lithium Ion (12V Max) Battery for continuous use and extended run-time
Christmas Sales Dremel 8200-1/28 12-Volt Max Cordless Rotary Tool Overview
Includes 12V Max Lithium-Ion Cordless Rotary Tool Kit - 8200-1/28-RT, 12V Max Lithium-Ion Battery, 12V Charger, Mandrel - EZ402, 1-1/2-in Reinforced Cut-Off Wheel - EZ456, Mandrel - 401, Mandrel - 402, High Speed Cutter - 191, Coarse 1/2-in Sanding Drum - 407, (2) Emery Cut-Off Wheel, (3) 1/2-in 120 Grit Sanding Band - 432, Aluminum Oxide Grinding Stone - 8193, Silicon Carbide Grinding Stone - 84922, Aluminum Oxide Grinding Wheel - 541, Aluminum Oxide Grinding Stone - 932, Emery Wheel - 425, Polishing Compound - 421, (2) 1/2-in Felt Polishing Wheel - 414, 1-in Felt Polishing Wheel - 429, (3) 1/2-in 60 Grit Sanding Band - 408, (2) 1/2-in 240 Grit Sanding Band - 445, (2) 3/4-in 180 Grit Sanding Disc - 411, MultiPurpose Cutting Bit - 561, Wrench, WrenchChristmas Sales Dremel 8200-1/28 12-Volt Max Cordless Rotary Tool Specifications
The 8200-1/28 12-Volt Max Lithium-Ion Cordless Rotary Tool Kit features Dremel's highest-performing, most versatile cordless rotary tool. Built for the most demanding applications, with a speed cut that's twice as fast as the leading cordless rotary tool, the 8200 arrives in a durable storage case with 28 Dremel accessories.
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 The Dremel 8200-1/28 Kit includes a durable storage case and 28 Dremel accessories. View larger. |
 The Dremel 8200 has an ergonomic body with 360-degree grip zone. View larger. |
Incredibly versatile, the 8200 cordless rotary tool has limitless uses, and it works with both standard attachments and Dremel EZ Lock accessories. Use it to polish beads, sand model airplane wings, carve a jack o' lantern, groom your dog's nails, engrave glassware, and more. Whether you're a serious hobbyist or an occasional do-it-yourselfer, you'll never run out of projects for this Dremel rotary tool.
Powerful Variable-Speed Motor
Powerful, user friendly, and built to last, the 8200 helps you complete a range of crafting, hobby, and artisan projects. It owes its robust performance to a powerful motor that offers maximum performance at all speed levels. The 8200 is so powerful, in fact, it has a speed of cut that's twice as fast as the competition's.
With the 8200, it's easy to match the speed to the job--the rotary tool offers variable speeds from 5,000 to 30,000 RPM. For further convenience, the speed dial is easy to read with increments that correspond directly to speed. Additionally, a separate on/off switch allows you to "set and forget" the speed setting, so you can stay focused on your project.
Lightweight 12-Volt MAX Lithium-Ion Battery
The 8200 rotary tool is powered by a removable 12-Volt MAX Lithium-Ion battery. The battery is exceptionally lightweight, so the tool is easy to handle and hold. The 8200-1/28 Kit includes a 12-Volt MAX Lithium-Ion battery and a one-hour charger for minimal downtime.
Soft-Grip, Ergonomic Body Provides Maximum Control
For maximum control over your projects, this handy tool features a slim, ergonomic body with a 360-degree grip zone. The soft grip keeps you working comfortably, especially during all-day or intricate jobs.
What's in the Box
Dremel 8200 12-Volt Lithium-Ion Cordless Rotary Tool, 565 Multipurpose Cutting Kit, Cutting Guide, EZ402 Mandrel, EZ456 1-1/2-Inch Reinforced Cut-Off Wheel, 401 Mandrel, 402 Mandrel, 191 High-Speed Cutter, 407 Coarse 1/2-Inch Sanding Drum, two 420 Emery Cut-Off Wheels, three 432 1/2-Inch 120-Grit Sanding Bands, 8193 Aluminum Oxide Grinding Stone, 84922 Silicon Carbide Grinding Stone, 541 Aluminum Oxide Grinding Wheel, 932 Aluminum Oxide Grinding Stone, 425 Emery Wheel, 421 Polishing Compound, two 414 1/2-Inch Felt Polishing Wheels, 429 1-Inch Felt Polishing Wheel, three 408 1/2-Inch 60-Grit Sanding Bands, two 445 1/2-Inch 240-Grit Sanding Bands, two 411 180-Grit 3/4-Inch Sanding Discs, 561 MultiPurpose Cutting Bit, Wrench, Storage Case, 12-volt Lithium battery, and one-hour charger.
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