Ever met someone who had a radio that covered half the planet?
They don’t have it now to demonstrate its amazing capabilities,
but they remember that it worked for miles and miles and only cost about £20
Seen brochures claiming that the particular radio being promoted will work over
a distance of anything from two to five miles or more?
So what’s happening, and what can really be expected?
Check the small print and you will find something like this (Taken from an actual brochure): The communication range quoted is calculated based on an unobstructed line of sight test under optimum conditions. Actual range will vary depending on terrain and conditions, and is often less than the maximum possible. Your actual range will be limited by several factors including, but not limited to: terrain, weather conditions, electromagnetic interference, and obstructions.
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The unlicensed radio market (PMR446) is very competitive, with each manufacturer trying to find a gimmick of some sort to increase their market share. So when one manufacturer decides to claim a maximum range under ideal conditions, all the other manufacturers tend to follow to remain competitive. So until there is a standard range test to which all manufacturers adhere to, it would be prudent to ere on the side of caution when looking at these claims.
As a matter of interest "the claimed" long distance record for a PMR446 radio is 535.8 km (333 miles) from the town of Blyth in the United Kingdom to the the city of Almere in the Netherlands. Lets hope the manufacturers don’t cotton on to this!
Back to reality: The actual range of a radio is dependent on many factors including environment (inner city range is far less than in open field), height above surrounding obstructions and to a very much lesser extent weather conditions. The radios receive sensitivity, the antenna type & effficiency will also affect the range of the radio. Good quality radios used "back to back " will in most conditions, work in a line off sight path, with range being gradualy reduced or even curtailed by any buildings or geographical features obstructing that path.
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Distorted speech quality: can often be attributed more to build quality than to “range” problems. After all in the real world you generally get what you pay for, and you cannot realistically expect, optimum aerials and premium voice quality to equate with radios costing from as little as £25 a pair that are built to a price for the consumer/hobby market.
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From our experience you can realistically expect with a commercial quality handportable PMR446 radio, a workable range of about three quarters of a mile to a mile outdoors, or about a half of a mile or less in a built up city environment. If additional range is needed for your application, licenced radios or a system useing licenced radios may be more appropriate.
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In the typical factory, hotel, school, leisure centre or swimming pool pure distance isn’t usually the main requirement. More likely the radio needs to be capable of penetrating walls between rooms and other obstacles with decent voice quality being the norm rather than the exception. This is where commercial PMR446 radios come into their own. They are usually built to the same standards as their licensed equivalent, achieving optimum transmit and receive capabilities due to higher quality materials being used in the manufacturing process.
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To your advantage, many PMR446 commercial/light industrial radios are being designed by the manufacturers to compete with their liceced peers on durability and how well they work rather than on cost alone.So if you have previously used budget radios in your environment and they didn’t perform as well as you would have liked, perhaps one of the commercial range of PMR446 radios could be more appropriate. Or you may wish to consider licenced radios which have recently come down in price to such an extent that there is little difference pricewise between the two options.
(SEE PMR446 or Licenced ).
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For those wanting to do there own calculations, here is a rule of thumb formula that may help:
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If it is accepted that the maximum distance is line of sight (to the horizon) how do we calculate this? Here is a basic formula for you, presuming the earth is a perfect sphere, it isn’t, there are no atmospheric problems, highly unlikely and nothing is in the way????. This simple formula gives a best-case approximation of the maximum propagation distance but not the quality of service at any location.
The square root of the height in metres multiplied by 3.57 gives a maximum propagation distance in kilometres.
Example lets take a typical eye level height 1.7 meters .
The square root (√) of 1.7 metres is 1.3038404 (Multiply this answer) by 3.57 = 4.6547102 kilometres
If you want the calculation in miles, then multiply that answer by 0.621371 = 2.89 miles.
For an observer standing on a hill or tower of 100 metres in height, the horizon is at a distance of (√) 100 =10 multiply by 3.57 =35.4 kilometres.
For an observer standing on a hill or tower of 100 metres (330 ft) in height, and the receiving station being at a height of 50 metres, the same calculations would apply, but useing the total height of the two points.
Example: Square root of 150 metres (12.247448 x 3.57 = 43.723389 kilometres.
For the Geeks go here: http://en.wikipedia.org/wiki/Line-of-sight_propagation
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