Where do you get the "what Motorola considers the reliable range" from?
Didn't Motorola hand out one of those cardboard slide rules with a "range calculator" at trade shows years ago?
Where do you get the "what Motorola considers the reliable range" from?
I have always heard that for radios without the use of repeaters, the general rule (for FM) is a range of ONE MILE for every HALF WATT (500 mw) of transmitter power. Centainly, tall landscapes will interfer, but is this a good general rule?
the distance to the radio horizon of a transmitter or receiver, in miles, is 1.34 times the height of the antenna, in feet.
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Er, no. Make that the square root of the height of the antenna, in feet. And it's in excess of what Motorola considers the reliable range, which leaves off the 1.34 multiplier.
I've seen a few general rules of thumb like this, but the general rule of thumb on that is, they're worthless. Look up the inverse square law on Google. That describes free space loss, and is as simple as it gets.
Take the height of your antenna in feet. Find the square root. That's your expected reliable range in miles. Do the same for the antenna on the other end, add the two results.
A pair of handie talkies: Antenna height, 5 feet. Range, 2.24 miles (each), for (call it) 4.5 miles expected reliable range. This is only over flat, unobstructed ground, though. Buildings and hills obstruct. At UHF, trees aren't helpful, either.
Now have one end stand on a 200 foot hill. Combining the two again, 16.5 miles.
Now, in reality, you may see as much as double this range, in perfect conditions. In not so perfect conditions, you may see half... or less.
Typical urban setting range between handie talkies is 1/2 to 1 mile, maybe 2 miles if you're lucky.
There are many "line of sight" calculators on the web. Here's one: Line Of Sight Calculator
Of course, these consider the world to be as smooth as a billiard ball.
Google Earth is a good resource. It shows the elevations for most of the earth. You can add the elevation to the formula.
Plus, if you bring up the Google Earth 'ruler tool', and draw a line between two points, you can save the path you created. Once you save it, the path line will change from yellow to red.
Now right click on the red line and choose "Show Elevation Profile". That will bring up a chart showing all the elevations between two points. It will show if there is a hill in the way that might block any signals.
There are many "line of sight" calculators on the web. Here's one: Line Of Sight Calculator
Of course, these consider the world to be as smooth as a billiard ball.
Google Earth is a good resource. It shows the elevations for most of the earth. You can add the elevation to the formula.
Plus, if you bring up the Google Earth 'ruler tool', and draw a line between two points, you can save the path you created. Once you save it, the path line will change from yellow to red.
Now right click on the red line and choose "Show Elevation Profile". That will bring up a chart showing all the elevations between two points. It will show if there is a hill in the way that might block any signals.
All the online calculators are not "line of sight", they are "free space" calculators and are only valid in space away from anything and everything including the earth. The are not accurate for calculating antenna gain/loss and distance for antennas on earth because ground bounce of signals off the earth can and do play havoc with the end result.
Thank you for this info about Google Earth!Google Earth is a good resource. It shows the elevations for most of the earth. You can add the elevation to the formula.
Plus, if you bring up the Google Earth 'ruler tool', and draw a line between two points, you can save the path you created. Once you save it, the path line will change from yellow to red.
Now right click on the red line and choose "Show Elevation Profile". That will bring up a chart showing all the elevations between two points. It will show if there is a hill in the way that might block any signals.